Microgreens Production with Sure to Grow Pads Trial

Source/Author/Date: Dr Lynette Morgan PhD, Suntec International Hydroponic Consultants, New Zealand, November 2008

Long Title: Comparison of Sure to Grow® Pads to 3 Other Growing Media for Production of Microgreens in a Standard NFT Tray Greenhouse System, Including Relative Growth rate Analysis and Postharvest Assessment, Arugula, Red Cabbage and Broccoli

The primary objective of this study was to compare the growth of 3 microgreens species (arugula, red cabbage and green broccoli), sown into 4 different pad/media products used in US commercial production, these being Cornell Peat-Lite Mix, horticultural grade perlite and vermiculite and the Sure to Grow® Pads for microgreens production.

RESULTS AND CONCLUSIONS

 

While there appeared to be many interactions with regard to season, species and media/pad treatment, the STG product consistently produced the highest quality harvested product and had the least post harvest problems at completion of the shelf life assessment. Yield and relative growth rate results were mixed and appear to be dependant on species. The STG Pads produced significantly higher yields than perlite in the Arugula crop in both sowing dates, but there was no significant effect of media/pad treatment for yield with the red cabbage. Relative growth rate analysis results showed a general trend of the perlite treatment having lower fresh and dry weight accumulation.

The main findings of this trial were:

Perlite consistently performed the poorest of all 4 media evaluated – in terms of yield, relative growth rate, product quality, particle contamination issues and disease occurrence. Peat-Lite, vermiculite and STG did not demonstrate any major contamination issues of the harvested product.

Peat-Lite, vermiculite, and perlite developed isolated disease outbreaks under warm and humid growing conditions despite good hygiene and sterilized water used during production. STG treatments remained disease free during the course of this trial. This trial was run under optimal spring growing conditions and results may differ under less than optimal environmental conditions or where disease pressure may be high.

Media treatment had a significant effect on plant quality and post harvest shelf life. Vermiculite and perlite are prone to post harvest rots and yellowing. STG produced seedlings which are more compact, less elongated then other treatments with a greater shelf life and fewer post harvest problems.

Peat-Lite appeared to have a slight germination advantage which may be due to the presence of organic compounds contained in peat such as humic acids. These could be beneficial as additives to STG systems during the early stages of germination. Peat-Lite significantly increased the EC of the nutrient solution flowing through the system due to the presence of fertilizer salts in this media. STG was the only media that had no influence on solution EC or pH.

STG has a clear and significant advantage in the efficiency and management of NFT microgreens production systems including greatly reduced set up and removal times, ease of irrigation management, and effective control of root zone moisture levels.

It appears that different species of microgreens respond to the physical properties of these growing media in different ways – in this trial Arugula was the species that significantly and consistently produced greater yields as well as higher product quality in STG, while there was no significant effect of treatment on Red Cabbage.

Based on the findings of this trial, the most significant advantages of the STG product are in a lower occurrence of disease during production and post harvest, ease of use, lower labor requirement for installation and removal, good physical root environment including drainage between irrigations and most importantly, improved microgreens product quality and greater shelf life.

Dr. Lynette Morgan PhD
Suntec International Hydroponic Consultants

INTERNATIONAL HYDROPONIC CONSULTANTS

 

 

 

Private and Confidential

 

Report Prepared for Sure to Grow®, 6062 Holdings, LLC, Beachwood Ohio, USA

 

A COMPARISON OF SURE TO GROW® PADS

TO 3 OTHER GROWING MEDIA FOR PRODUCTION

OF MICROGREENS IN A STANDARD NFT TRAY

GREENHOUSE SYSTEM, INCLUDING RELATIVE

GROWTH RATE ANALYSIS and POST HARVEST ASSESSMENT

Arugula, Red Cabbage and Broccoli

 

 

 

 

Dr Lynette Morgan PhD

Suntec International Hydroponic Consultants

New Zealand

November 2008

 

A COMPARISON OF SURE TO GROW® PADS

TO 3 OTHER GROWING MEDIA FOR PRODUCTION

OF MICROGREENS IN A STANDARD NFT TRAY

GREENHOUSE SYSTEM, INCLUDING RELATIVE GROWTH RATE ANALYSIS and POST HARVEST ASSESSMENT

Arugula, Red Cabbage and Broccoli

 

EXECUTIVE SUMMARY

 

The objectives of this study were to:

 

  1. Compare the relative growth rate of 3 microgreens species (arugula, red cabbage and green broccoli), sown into 4 different pad/media products used in US commercial production, these being Cornell Peat-Lite Mix, horticultural grade perlite and vermiculite and the Sure to Grow® Pads for microgreens production.

 

  1. To compare harvested fresh weight and quality of microgreens grown in 4 different pad/media products including post harvest shelf life assessment.

 

  1. To assess various aspects of microgreens production in each of 4 media/pad products including occurrence of disease, changes in nutrient solution EC and pH, ease of use, salt build up, time required for set up and crop removal and disposal of spent media.

 

Crop trials were run in the early to mid spring 2008 period under standard greenhouse conditions using 4 separate wide channel NFT systems filled with each of the growing media/mat treatments. Each treatment system had a separate nutrient tank and irrigation system. Nutrient solution was applied after germination at an EC of 0.5 mS cm-1 and a pH of 5.8. Microgreens seeds were sown at high rates of 230 g/m2 for Arugula and 460 g/m2 for red cabbage and broccoli and misted as required during the germination phase. Channels with covered with fine horticultural cloth to maintain humidity for the first 72 hours. Trials were run over two successive planting dates and treatments randomly assigned to channels for each sowing. Average day temperatures during these trials were 16 – 24o C (61 – 75o F) day and 12 – 16o C (54 – 61o F) night with a mix of cloudy overcast and bright days. Humidity level ranged from 70 – 92% with air movement across the crop assisted by a greenhouse fan. During the trial factors such as time taken to install and remove each media treatment, effect of treatments on solution EC and pH, disease occurrence, media moisture and temperature levels and general plant appearance were noted.

 

During these trials, samples of 100 seedlings from each treatment and species were taken every 3 days for relative growth rate assessment. Fresh and dry weight was recorded for each treatment and an analysis of relative growth rate expressed in g/day of fresh and dry weight was determined.

 

At harvest, fresh weight from each plot was recorded, a long with an assessment of the overall quality from each treatment. Samples were taken for shelf life determination and visible signs of product deterioration over time were noted.

 

 

RESULTS AND CONCLUSIONS

 

While there appeared to be many interactions with regard to season, species and media/pad treatment, the STG product consistently produced the highest quality harvested product and had the least post harvest problems at completion of the shelf life assessment. Yield and relative growth rate results were mixed and appear to be dependant on species. The STG Pads produced significantly higher yields than perlite in the Arugula crop in both sowing dates, but there was no significant effect of media/pad treatment for yield with the red cabbage. Relative growth rate analysis results showed a general trend of the perlite treatment having lower fresh and dry weight accumulation.

 

The main findings of this trial were:

 

Perlite consistently performed the poorest of all 4 media evaluated – in terms of yield, relative growth rate, product quality, particle contamination issues and disease occurrence. Peat-Lite, vermiculite and STG did not demonstrate any major contamination issues of the harvested product.

 

Peat-Lite, vermiculite and perlite developed isolated disease outbreaks under warm and humid growing conditions despite good hygiene and sterilised water used during production. STG treatments remained disease free during the course of this trial. This trial was run under optimal spring growing conditions and results may differ under less than optimal environmental conditions or where disease pressure may be high.

 

Media treatment had a significant effect on plant quality and post harvest shelf life. Vermiculite and perlite are prone to post harvest rots and yellowing. STG produced seedlings which are more compact, less elongated then other treatments with a greater shelf life and fewer post harvest problems.

 

Peat-Lite appeared to have a slight germination advantage which may be due to the presence of organic compounds contained in peat such as humic acids. These could be beneficial as additives to STG systems during the early stages of germination. Peat-Lite significantly increased the EC of the nutrient solution flowing through the system due to the presence of fertiliser salts in this media. STG was the only media which had no influence on solution EC or pH.

 

STG has a clear and significant advantage in the efficiency and management of NFT microgreens production systems including greatly reduced set up and removal times, ease of irrigation management, and effective control of root zone moisture levels.

 

It appears that different species of microgreens respond to the physical properties of these growing media in different ways – in this trial Arugula was the species which significantly and consistently produced greater yields as well as higher product quality in STG, while there was no significant effect of treatment on Red Cabbage.

 

Based on the findings of this trial, the most significant advantages of the STG product are in lower occurrence of disease during production and post harvest, ease of use, lower labour requirement for installation and removal, good physical root environment including drainage between irrigations and most importantly, improved microgreens product quality and greater shelf life.

 

Dr Lynette Morgan PhD

Suntec International Hydroponic Consultants

New Zealand

Private and Confidential – Report prepared for Sure to Grow®,6062 Holdings, LLC,

Beachwood, Ohio USA

 

A COMPARISON OF SURE TO GROW® PADS

TO 3 OTHER GROWING MEDIA FOR PRODUCTION

OF MICROGREENS IN A STANDARD NFT TRAY

GREENHOUSE SYSTEM, INCLUDING RELATIVE GROWTH

RATE ANALYSIS and POST HARVEST ASSESSMENT

 

Arugula, Red Cabbage and Broccoli

 

INTRODUCTION

Hydroponic microgreens are a relatively new crop which utilise a wide range of plant species. Microgreens are defined as being larger than a sprout and having fully expanded cotyledons, however some growers harvest at a later stage with up to four true leaves. In contrast to sprouts, microgeens are typically grown under natural or artificial lights during the entire production cycle.

 

Microgreens originated in California where innovative chefs started using them to incorporate color, flavor and texture into their dishes – a trend which has rapidly spread across the USA. Now microgreens are being produced commercially in many countries and the diversity of production methods and species grown is ever increasing. Microgreens appear as toppings, garnishes and flavorings in salads and feature in many up-market dishes as well as being sold in produce stores and supermarkets.

 

What makes microgreens so unique is the diversity of crop species being produced and the fact they are incredibly well suited to hydroponic production. Unlike baby salad greens or mesclun mixes which are commercially grown and mechanically harvested on a large scale outdoors in soil, microgeens need careful attention to detail and prevention of contamination with grit particles. Greenhouse or indoor production methods are well suited to microgreens production as plants grow in soilless media with high cleanliness and hygiene requirements.

 

Various hydroponic systems are currently used for microgreens production with the `long tray’ system growing in popularity. These are often modified, wide NFT channels into which hydroponic nutrient solution is supplied via emitters. These channels are typically either filled with a granular growing media or grow mat which holds the seed in place during the germination phase and provides a reserve of moisture. Nursery tray and bed systems are also in use for smaller scale microgreens production, many of which incorporate the use of overhead watering which poses an additional disease risk through wetting of the foliage. Many commercial growers have adapted NFT channels and technology to microgreens production, although there is now a range of specific microgreens production systems on the market that incorporate tiered systems and flood and drain tables.

 

The majority of microgreens producers use climate-controlled greenhouses for year round production. However, many microgreens species are sensitive to excessive heat and humidity and in tropical climates, microgreens may be grown in chiller rooms or refrigerated shipping containers using artificial lighting. Microgreens require careful attention to nutrition as factors such as nutrient ratios, EC and pH can influence not only yields, but also quality and shelf life of the harvested product. Microgreens are different from sprouts in their nutritional requirements and require a dilute nutrient solution to be applied to maintain foliage quality and growth rates. Initially, microgreens seeds can be germinated in water, however once the cotyledons are visible and starting to develop chlorophyll, the seedling will have exhausted the reserves contained in the seed. At this stage, the young plant is starting to photosynthesize and produce its own assimilate, and nutrient ions will be absorbed by the root system. EC levels are typically run at seedling strength for microgreens, although they may be adjusted for season. There is some scope to manipulate growth of microgreens with use of EC. Higher EC can be used to boost colour development in red types during low winter light or warm growing conditions. Control of EC will also affect shelf life of cut greens. The moisture holding capacity of the growing media used in microgreens production will influence product quality and disease occurrence. Media with a high moisture holding capacity are likely to produce softer growth which may wilt more rapidly post harvest. Free draining media will produce a `harder’ plant, but may not hold sufficient moisture between irrigations.

 

Currently a number of different substrates are used for microgreens production, these include paper towel, burlap sheets, perlite, vermiculite, peat based media, organic mixes and matting such as the Sure to Grow® product. All granular media pose a contamination risk with particles of substrate which may get carried with the seedlings at harvest while some media are more prone to disease outbreaks which can be common at the high density microgreens seeds are sown at.

 

Perlite

Perlite is a natural volcanic material produced by heating the ground material to 1000oC. Perlite is often used as a component of potting mixes and as a hydroponic growing media for a wide range of crops such as tomatoes, cucumbers and melons. Expanded perlite is very light with bulk density of 0.1 g cm-3. Perlite is very porous and can hold 3 – 4 times its weight of water. Perlite is neutral with a pH of 7.0 – 7.5, and has little buffering capacity and is considered to be inert (contains no mineral nutrients). Perlite is sterile after manufacture and can be steamed between crops.

 

Vermiculite

Vermiculite is formed by heating a natural clay mineral to 1000oC, during which the water contained within the mineral becomes a vapour and expanded the particles. As a result light weight particles are formed which have a high porosity. Vermiculite is typically used as a germination media or as a component of potting mixes. The bulk density of expanded vermiculite is 0.1 g cm-3 with a strong capillary action and an ability to hold 3-4 times its own weight in water. Vermiculite is neutral with a pH of 7.0 – 7.5 and low EC. It retains a permanent negative charge and consequently it has a CEC (Cation exchange value) of 150 – 210 mmolc Kg-1 . Vermiculite has the ability to absorb ions such as phosphate due to its high surface area and some positive charged sites on the edges of the mineral it is composed of.

 

Cornell Peat –Lite Mix

This is a growing media comprised of 50% sphagnum peat moss and 50% vermiculite with additional fertilizers. A number of different Cornell mixes exist for different applications from seedling production through to ornamental container mixes. Cornell Peat-Lite mixes can be purchased pre made or produced by growers on site. Peat is an organic material formed as a result of partial decomposition of plants, including species of sedges, grasses and mosses, under cool temperatures and anaerobic or semi-anaerobic conditions. Peat has a very high water holding capacity and is included in container mixes for this reason. Wetting agents are often used with peat to overcome its hydrophobic nature. Sphagnum peat contains at least 95% organic matter and has a fibrous structure with a high surface charge density including cation exchange capacity. Sphagnum is usually characterised by an acidic pH (pH 3 – 5) and in most cases lime or dolomite is added to increase the pH up to the range 5 – 6. Although sphagnum moss has been found in some cases to contain specific fungistatic substances, it is generally considered as a substrate conducive to numerous soilborne diseases. The sterilisation of peat, although possible, does not alleviate the problem, as it leaves a biological vacuum that can easily be filled by pathogenic fungi (Raviv et al, 2002).

BACKGROUND

 

The Sure to Grow® Pad for microgreens is a unique product which has been designed to provide a moisture retentive, sterilized seed bed for use in a range of hydroponic production systems. The product is lightweight, clean, easy to install and remove and provides both aeration and moisture for the germinating seed and nutrient uptake by the young seedling.

 

The main objective of this study was to compare the growth, yields and quality of 3 species of commonly grown microgreens with other commonly utilised substrates.

 

OBJECTIVES

 

  1. To compare the relative growth rate of 3 microgreens species (arugula, red cabbage and green broccoli) sown into 4 different pad/media products used in US commercial production.

 

  1. To compare harvested fresh weight and quality of microgreens grown in 4 different pad/media products, including post harvest shelf life assessment.

 

  1. To assess various aspects of microgreens production in each of 4 media/pad products including occurrence of root disease, changes in nutrient pH, ease of use, salt build up, time required for set up and crop removal and disposal of spent product.

 

 

TREATMENTS:

 

  1. Sure to Grow® Pad seedling mat product (STG)
  2. Horticultural grade perlite
  3. Horticultural grade vermiculite
  4. Cornell Peat-Lite Mix (peat moss/vermiculite/fertilisers)

 

 

Each treatment was sown with 3 microgreens species

 

    1. Red cabbage (Brassica oleracea)
    2. Arugula (Eruca sativa)

(iv) Broccoli (Brassica oleracea)

MATERIALS AND METHODS

Each of the four growing pad/media treatments were installed in separate NFT, (4m long, 24 cm / 13 feet long x 9 inches wide channels), seedling systems complete with individual reservoirs, channels and nutrient solutions. This is to determine the potential effect of each media/mat product on the nutrient solution EC and pH over the course of the trial and to assess any problems (such as particle blockages) which each treatment may create. Each separate NFT system consisted of 2 x 4 meter (13 feet) long standard wide based channels through which water, then nutrient flowed during the course of crop development.

 

A given weight of seed of each microgreens species was sown in the channels onto the surface of each of the 4 media/pad treatments. This was at rates of: 230 g/m2 for arugula, and 460 g/m2 for red cabbage and broccoli seed. Seed was misted with water and covered with light frost cloth material and left to germinate for 48 hours with intermittent misting as required. After germination, channels were irrigated via a small submersible pump in each system reservoir. Drip irrigation was applied after cotyledon expansion in all 3 species; a complete hydroponic seedling nutrient solution was applied to each system at an EC of 0.5 mScm-1 and pH of 5.8. This was adjusted and maintained daily until completion of each trial.

 

Once germination had occurred, relative growth rate assessment (RGR) was carried out on each species, in each media/pad treatment. RGR is a method of assessing the increase in plant dry weight/per day and is an important determinant of crop productivity. A random sample of plants from each treatment and species was collected every 3 days – fresh and dry weight of these seedlings was determined at each assessment date.

 

Microgreens were grown through to harvest maturity – Approximately 2 – 2.5 inches (5cm) for arugula, red cabbage and broccoli. At this stage, each plot was harvested by cutting at the base of the plants just above the roots, with some allowance for avoiding contamination with substrate particles. Plots were assessed for total fresh weight and quality.

 

Shelf life assessment: At harvest, 3 samples of each species from each media/mat treatment (total of 48 samples) were collected for post harvest shelf life assessment. 30 g of foliage was packaged into sealed polyethylene bags and stored under refrigeration (2o C, 36o F). Appearance, including rots, fungal growth, yellowing or other loss of colour, and turgidity was assessed until samples reached the end of their acceptable shelf life. Photographs were taken of each sample, after removal from the bags, at trial completion.

 

During the course of this trial, each media treatment was monitored for the presence or development of disease/root rot symptoms, root health, salt build up on the surface of the media or other production problems. Time taken to set up each separate media/pad treatment system was recorded, as well as time taken to remove each media/pad product post harvest from the hydroponic system.

 

The first sowing commenced on 18 September and was harvested on 5 October 2008. The second sowing commenced on 17 October 2008 and was harvested on 5 November 2008. These dates were during the early – mid spring period with average day temperatures of 16 – 24o C (61 – 75o F) and night temperatures of 12 – 16o C (54 – 61o F).

 

RESULTS

 

CROP OBSERVATIONS

 

Planting one (sown 16 September)

Germination progressed rapidly in all species – arugula was the first to germinate in 48 hours, followed by red cabbage and broccoli which had germinated within 72 hours. Germination was similar in all treatments by day 5, however there was a slight advancement in visible size with the Peat-Lite seedlings in the first 2 – 3 days. By day 7 seedlings were well developed with vigorous growth. Rapid germination in the perlite treatment had thrown up some of the larger perlite particles which were sitting on top of the canopy of seedling leaves. These were sprayed with water to try and settle the particles back down onto the growing bed, however some remained. This did not occur in the heavier media (vermiculite and peat-Lite).

 

Temperature readings were taken of each media treatment on warm days to determine if thermal differences existed.

 

By day 13 colour differences were visible between treatments – the peat-Lite red cabbage seedlings were a dark green/red color compared to the STG and perlite red cabbage which had a deeper red/purple coloration.

 

At harvest some small patches of white fungal growth was noted around the base of a small number broccoli and red cabbage seedlings in the peat-Lite and vermiculite treatments, but this did not seem to affect harvest yields. The perlite treatment was the most difficult and time consuming to harvest due to the particles of perlite which contaminated the product and created an uneven bed surface due to having been lifted up as the seed germinated. The peat-Lite treatment resulted in elongated seedlings with long, thin stem sections, perlite resulted in most compact plants.

 

Planting two (Sown 17 October)

Germination progressed rapidly in all species, however the germination advancement noted in the Peat-Lite treatment in planting one was more pronounced in planting two. The Peat-Lite treatment seed appeared to develop radicle emergence several hours earlier than any other treatment – this may be due thermal differences between the different seed bed media or the presence of organic stimulant compounds in the peat (humic acids).

 

The perlite treatment again developed patches of perlite particles thrown up onto the top of the seedling canopy during germination, which proved difficult to remove without damaging the crop. Largest differences in seedling size between treatments were seen in the arugula – the Peat-Lite produced visibility larger seedlings, due to these having an elongated stem section. Perlite and STG produced more compact, stronger and deeper coloured seedlings.

 

By 24 October, some small patches of fungal disease outbreak were noted in the perlite arugula, possibility due to high humidity and warm growing conditions in the greenhouse. By the time of harvest there were isolated disease outbreaks in the Peat-Lite, vermiculite and perlite argulua treatments which affected yield data slightly. A further disease outbreak occurred in the perlite broccoli close to harvest which resulted in significant losses in yield. The STG treatment had no visible signs of disease at harvest.

 

 

Thermal readings

Temperature readings were taken during planting 1 and 2 using a non destructive infra red thermometer to record air, canopy and media temperature between the different treatments – a summary of which is provided below:

 

Conditions: Warm, high radiation, mid afternoon temperatures

 

Crop stage: one week before harvest, good canopy cover.

 

Air temperature (greenhouse average) 23.4o C (74.1o F)

Peat-Lite canopy 25o C (77.0o F)

Peat-Lite root zone 21.7o C (71.1o F)

 

STG canopy 25o C (77.0o F)

STG root zone 27o C (80.6o F)

 

Vermiculite canopy 24o C (75.2o F)

Vermiculite root zone 25.2o C (77.4o F)

 

Perlite canopy 22o C (71.6o F)

Perlite root zone 23o C (73.4o F)

 

 

EC and pH – System observations

It is well known that various hydroponic media can influence the EC and pH of the nutrient solution applied. In this trial it was found that the Peat-Lite substrate significantly increased the EC of the nutrient solution and this was due to the presence of fertiliser salts incorporated into the Peat-Lite mix before planting, some of which are highly soluble. EC levels in the Peat-Lite nutrient solution increased from the initial 0.5 mS.cm-1 to 3.2 mS.cm-1 within 48 hours, although this did not appear to have any negative impact on plant growth. pH levels in the Peat-Lite nutrient solution fell from 5.8 to 5.5 which is most likely due to the acidification by the peat.

 

The EC in the vermiculite system did not change significantly through out the course of the trial, however the pH of this system increased rapidly from 5.8 to 7.7 within 28 hours of applying the nutrient solution.

 

The STG mats appeared to have no influence on the composition of the nutrient solution, EC remained stable and pH stabilised at 6.0 – a slow increase in pH is considered normal under hydroponic production.

 

The perlite treatment also had no effect on the EC of the nutrient solution, although pH levels rose to 6.5 within the first 48 hours and then stabilised for the rest of the trial.

No mineral deficiencies or toxicities were noted on any plants during either planting date and it is unlikely, based on crop observations, that EC and pH changes caused any major problems during the short growth period of each planting as solutions were completely replaced every 5 days.

 

During the course of both plantings differences in the moisture holding capacity between irrigations of the different growing media was noted. The Peat-Lite and vermiculite treatments become over-saturated rapidly and held moisture for longer than the STG pads or the perlite treatment. Perlite had a tendency to be well irrigated on the base of the channel and drier towards the top of the seed bed – i.e capillary action was not as great as in the vermiculite media. The STG mats drained well between irrigations, but held sufficient moisture for plant growth without over saturation. Maintaining good moisture status of the STG treatment was relatively simple as the mats could be pulled back to check root moisture levels (and root health) and the rate of drainage ensured that over watering was not a problem. The STG treatment was however observed to heat up the nutrient solution more than the other treatments during warm growing conditions.

SYSTEM SET UP AND MEDIA REMOVAL

The time required by one person to prepare and install the individual growing media into each NFT system (2 x 4 meter / 13 feet length channels), then remove the spent media after harvest was recorded:

 

Media treatment Time taken for installation and removal per channel

(4m long x 24 cm wide / 13 feet long x 9 inches wide)

 

Peat-Lite 9 minutes installation* (does not include 30

minutes to weigh out fertilizers and manufacture the mix).

Removal 16 minutes

 

Vermiculite 8.5 minutes to install*

Removal 17 minutes

 

Perlite 8.5 minutes to install*

Removal 16 minutes

 

STG Pad Less then 1 minute to install

Removal 4.5 minutes

 

*Some microgreens growers re-use Peat-Lite, Vermiculite and Perlite, which requires removal of roots and crop debris from the media between crops. In these operations “installation time” between crops increases may differ from time required for replacement.

 

 

  • Installation included scooping or pouring media into channels, levelling and wetting up to run off with a hand held sprinkler.
  • Removal included scooping damp media and root systems out of channels, removing from the greenhouse and rinsing channels down to removal particles. STG pads were rolled up and removed.
  • Timings included installation and removal of one additional channel per treatment containing wheatgrass root systems.

 

RELATIVE GROWTH RATE

 

Relative growth rate is a measure of fresh and dry weight production expressed as grams per day per 100 seedlings and is shown in Tables 1 and 2. Means not separated by standard errors (s.e) are not significantly different

 

Table 1 Relative growth rate (grams of fresh weight accumulation per day), by species.

 

ARUGULA

Planting 1 Planting 2
Treatment g/day s.e g/day s.e
Perlite0.2570.0240.3520.044
Vermiculite0.2730.0240.3410.026
Sure to Grow®0.3020.0470.4160.015
Peat Lite

 

BROCCOLI

0.2550.0240.3230.077
Planting 1 Planting 2
Treatment

 

g/day s.e g/day s.e
Perlite0.3100.0140.3020.049
Vermiculite0.3770.0310.3490.014
Sure to Grow®0.3760.0060.5450.054
Peat Lite

 

RED CABBAGE

0.3930.0460.4940.047
Planting 1 Planting 2
Treatment g/day s.e g/day s.e
Perlite0.3110.0370.3450.060
Vermiculite0.3510.0160.3530.037
Sure to Grow®0.3550.0200.6070.138
Peat Lite

 

 

 

0.3220.0430.7950.199

Table 2. Relative growth rate (grams of dry weight accumulation per day), by species.

 

ARUGULA

Planting 1 Planting 2
Treatment g/day s.e g/day s.e
Perlite0.0050.0030.0170.010
Vermiculite0.0150.0040.0220.007
Sure to Grow®0.0170.0050.0250.002
Peat Lite

 

BROCCOLI

0.0180.0040.0220.009
Planting 1 Planting 2
Treatment g/day s.e g/day s.e
Perlite0.0150.0040.0160.0034
Vermiculite0.020.0090.0170.0049
Sure to Grow®0.01670.000.0260.0087
Peat Lite

 

RED CABBAGE

0.0250.0060.0260.0073
Planting 1 Planting 2
Treatment g/day s.e g/day s.e
Perlite0.010.00230.0310.0153
Vermiculite0.02160.00290.0210.0093
Sure to Grow®0.01670.000.0240.0122
Peat Lite0.02170.00290.0380.0157

 

Relative growth rate analysis for Arugula in planting one show that there was no significant difference in fresh weight (no differences between any of the 4 treatments). However, the dry weight accumulation was significantly lower in the perlite treatment for this planting date, while the vermiculite, Sure to Grow® and Peat-Lite were not significantly different from each other. For the second planting date, the Sure to Grow® treatment had significantly greater fresh weight accumulation than all other treatments. The perlite vermiculite and Peat-Lite treatments where not significantly different from each other. The dry weight was not significantly different in any treatment.

 

For broccoli in planting one, fresh weight values were significantly lower in the perlite treatment, all other treatments were not significantly different. There were also no significant differences in dry weight between treatments. For the second planting date, both the Sure to Grow® Pad and Peat-Lite had significantly higher fresh weight accumulation than the perlite and vermiculite treatments. There was no significant difference between dry weight accumulation for any treatment.

 

For red cabbage in planting one, there was no significant difference in fresh weight accumulation between all 4 treatments. Dry weight accumulation was significantly lower in the perlite treatments compared to the vermiculite, Sure to Grow® and Peat-Lite. For planting two, the Sure to Grow® and Peat-Lite fresh weight accumulation was significantly higher than the perlite and vermiculite values. No significant differences existed between all four treatments in the dry weight accumulation values.

 

 

YIELDS

 

Table 1, gives the final yield data in grams of harvested product per area of bed sown/plot (approximate area is 23 cm x 120 cm or 9 inches x 47 inches), by treatment and planting.

 

Table 1

 

ARUGULA (amount of seed sown per plot = 69 g, 2.4 oz)

 

TreatmentPlanting 1Planting 2
Peat-Lite424.5 * g (15.00 oz.)533* g (18.80 oz.)
STG474.2 g (16.73 oz.)546 g (19.26 oz.)
Vermiculite473 g (16.68 oz.)467* g (16.47 oz)
Perlite400.g (14.11 oz.)388* g (13.69 oz.)

 

• = presence of some fungal disease at harvest may have affected yields

 

RED CABBAGE (amount of seed sown per plot = 138 g, 4.87 oz)

 

TreatmentPlanting 1Planting 2
Peat-Lite466 g (16.44 oz.)405 g* (14.29 oz.)
STG467 g (16.47 oz)459 g (16.19 oz.)
Vermiculite471 g (16.61 oz.)433 g (15.27 oz.)
Perlite416 g (14.67 oz.)413 g (14.57 oz.)

 

• = presence of some disease at harvest

 

BROCCOLI (amount of seed sown per plot = 138 g, 4.87 oz)

 

TreatmentPlanting 1Planting 2
Peat-Lite674.5 g (23.79 oz.)592 g (20.88 oz.)
STG643 g (22.68 oz.)622 g (21.94 oz.)
Vermiculite628 g (22.15 oz.)539 g (19.01 oz.)
Perlite515 g (18.17 oz.)181 g* (6.38 oz.)

 

• – significant disease reduced yields in this treatment

 

A Chi square analysis of the final harvest data for each species found that significant treatment differences (P = 0.05) in yield existed in the Arugula for both planting dates. Yield was not significantly different between the treatments for red cabbage in either planting date. Broccoli yield differences were significant for planting one, but not for planting two due to the presence of outlier data caused by a disease outbreak in the perlite treatment.

 

 

Figure 1 Arugula Final Yield (grams of fresh weight)

 

Arugula Final Yield per bed

0

100

200

300

400

500

600

Peat-Lite

Sure-to-Grow®

Vermiculite

Perlite

Treatment

Yield (grams)

Planting 1

Planting 2

Figure 2 Broccoli Final Yield (grams of fresh weight)

Broccoli Final Yield

0

100

200

300

400

500

600

700

800

Peat-Lite

Sure-to-Grow®

Vermiculite

Perlite

Treatment

Yield (grams)

Planting 1

Planting 2

 

 

 

Figure 3 Red Cabbage Final Yield (grams of fresh weight)

Red Cabbage Final Yield per Bed

360

380

400

420

440

460

480

Peat-Lite

Sure-to-Grow®

Vermiculite

Perlite

Treatment

Yield (grams)

Planting 1

Planting 2

 

YIELD PER SQUARE METER/SQUARE FOOT EQUALIVANTS (per planting)

 

ARUGULA

 

Treatment Planting 1 Planting 2
g/m2 oz/ft2 g/m2 oz/ft2
Peat-Lite1538*5.051721.65.34
STG18185.641978.26.50
Vermiculite1713.75.631691.9*5.56
Perlite1449.24.761405.74.62

 

• = presence of some fungal disease at harvest may have affected yields

 

RED CABBAGE

 

Treatment Planting 1 Planting 2
g/m2 oz/ft2 g/m2 oz/ft2
Peat-Lite 1688.3 5.541467.3*4.82
STG 1691.9 5.5616635.46
Vermiculite 1706.4 5.601568.85.15
Perlite 1507.2 4.95

 

• = presence of some disease at harvest

 

BROCCOLI

 

1496.34.91
Treatment Planting 1 Planting 2
g/m2 oz/ft2 g/m2 oz/ft2
Peat-Lite2443.78.032144.87.04
STG2329.57.652253.57.40
Vermiculite2275.27.471952.86.41
Perlite1865.86.13655.8*2.15

 

HARVEST QUALITY

 

The quality of each treatment plot and species was assessed at the time of harvest. High quality microgreens should be well developed with expansion of the first true leaves, clean stem area and freedom from media particles with no evidence of tissue breakdown. Colour should be uniform and characteristic of the species being grown. Plants should not be overly succulent, thin, weak or pale as this results in a shorter post harvest shelf life. Packaged microgreens should be free of all fungal and bacterial pathogens which may cause post harvest rots during storage.

 

 

ARUGULA

Peat-Lite: Planting one: Some lower stem rot noted in bed at harvest – presence of fungal mycelium on base of plants. Colouration light green, seedlings tall and `thin’ and light in weight for size, although size was good. Very low level of contamination with peat particles.

Root healthy acceptable, some brown roots at base of bed noted.

Planting two: Approximately 10% of bed lost due to disease (fungal). Quality good, medium green colour, growth overly soft, stems long but white. Some yellowing noted on lower leaves.

 

STG: Planting one: Good green colouration, clean white stems, consistent height, although plants shorter than in the Peat-Lite treatment. Seedlings more compact.

Planting two: Good quality, short compact plants, mid green colour

 

Vermiculite: Planting one: Good colour, no particle contamination, some yellowing on lower leaves.

Planting two: Very slight vermiculite particle contamination, lower leaves have some yellowing, possibility due to presence of disease on bed at harvest. Colour slightly pale.

 

Perlite: Planting one: No disease presence, moderate contamination with perlite particles through harvested product, color good, shorter and compact plants compared to vermiculite and Peat-Lite.

Planting two: Moderate particle contamination, seedlings small in size compared to other treatments.

RED CABBAGE

Peat-Lite: Planting one: Color more diluted than other treatments, more green coloration and less deep red color development. Some slight rot on lower stems, stems wet.

Planting two: Lack of deep red/purple color which should be present on this species. Stems long and clean, seedlings slightly elongated. Leaves large and succulent, some fungal disease noted.

 

STG: Planting one: Darker red color than Peat-Lite, shorter and more compact seedlings than Peat-Lite or vermiculite treatments.

Planting two: Plants healthy and compact, shorter than Peat-Lite or vermiculite

 

Vermiculite: Planting one: Quality good, plants tall.

Planting two: Color good, small leaf size with long stems, some fungal development beginning on bed which has not affected the seedlings.

 

Perlite: Planting one: Some perlite contamination of harvested product. Seedlings shorter and noticeably smaller than other three treatments, color good.

Planting two: Small leaves, darker color, and moderate perlite contamination.

 

 

BROCCOLI

Peat-Lite; Planting one: Long stems, succulent growth, large leaves, color medium green. Planting two: Very long white stems, dark green color, good quality.

 

STG: Planting one: Very dark green coloration, uniform leaf size and height, clean white stems.

Planting two: Very dark green, high quality, shorter and more compact plants than Peat-Lite.

 

Vermiculite: Planting one: Good green coloration, some slight yellowing of older leaves. Planting two: Thin stems, light green coloration, and small size.

 

Perlite: Planting one: Uneven heights of seedlings, color good, moderate particle contamination, short plants.

Planting two: 40% of bed lost to black spot on foliage (not marketable), seedlings small, light weight, pale green color with some yellowing of lower leaves.

 

SHELF LIFE ASSESSMENT

ARUGULA

Planting 1 harvested 5 October – shelf life assessment on 15 October

 

Treatment Comments
Peat-LiteSlight yellowing, and loss in color. Rot developed from day 4 onwards in one sample.
Sure To GrowSlight yellowing, particularly of older leaves by day 8. Small amount of wet rot in one sample by day 8.
VermiculiteTissue disintegration by day 8 in all samples, some yellowing of foliage
PerliteSome wilting, older leaves developing some brown necrotic developing by day 9. Wet rot in all samples by day 10

 

 

Planting 2 harvested 5 November – shelf life assessment 15 November

 

 

Peat-LiteYellowing on lower leaves and some wilt in one sample. Extensive brown rot and wet disintegration of foliage in 2 samples developing on day 8.
Sure to GrowGood green color, some minimal yellowing on older leaves, slight rot of older leaves in one sample developing by day 8.
Vermiculite2 samples extensive wet rot and breakdown plus foliage and yellowing seen at day 10.
PerliteSome yellowing with black lesions on 30% of foliage. Some wilting and loss of turgor. Pale green coloration developing on day 5.

 

 

 

 

Planting one Planting two

 

BROCCOLI

Planting 1 harvested 5 October – shelf life assessment on 13 October

 

Peat-LiteSignificant yellowing of foliage and loss of chlorophyll starting from day 6.
Sure To GrowSome yellowing and slight necrosis in 5 % of sample by day 8.
VermiculiteTissue break down, wet rot in all samples, starting on day 6.
PerliteTissue blackening and breakdown on samples starting on day 6.

 

Planting 2 harvested 5 November – shelf life assessment on 14 November

 

Peat-LiteSome wilting and slight loss of green color by day 9.
Sure to GrowSome wilting and slight loss of green color by day 9.
VermiculiteWilting and loss of color, yellowing and slight rot developing on day 8.
PerliteSignificant wilting and yellowing starting on day 7.

 

 

 

Planting 1 Planting 2

RED CABBAGE

Planting 1 harvested 8 October – shelf life assessment on 20 October

 

Peat-LiteSome wilting and slight loss of foliage color, foliage legions, by day 10.
Sure to GrowSlightly paler color, still in good condition by day 12.
VermiculiteSome wet rot and tissue breakdown developing on day 10.
PerliteWet rot and tissue breakdown in all samples by day 7.

 

Planting 2 harvested 5 November – assessed on 14 November

 

Peat-LiteSome yellowing and loss of color, slight wet rot by day 9.
Sure to GrowSome loss of red color, slight marketing on leaves, foliage still t
turgid.
VermiculiteWet rot and some tissue breakdown developing by day 5, color still acceptable.
PerliteSignificant wet rot and disintegration, some wilting starting at day 5.

 

 

Planting 1 Planting 2

 

CONCLUSIONS

 

Crop Observations

In both planting dates germination was rapid and vigorous and occurred within 48 hours of sowing. The Peat-Lite treatment appeared to have a slight germination advantage in both sowing dates with more rapid radicle emergence. This may have been due to the darker colored Peat-Lite seed bed warming faster and holding heat for longer, giving a germination advantage during this early spring period. It may also have been due to the presence of certain organic stimulant compounds such as humic acid present in peat which are proven to boost germination in many species. By day 7, all treatments appeared to have seedlings of a similar size and this germination advancement in the Peat-Lite treatment did not lead to any generalised significant increase in final yields. If humic acids are playing a role in germination enhancement in the Peat-Lite treatment, this advantage could also be used in all other inert media with a spray or soak application of humic acid products onto the seed bed surface. If the germination advantage of the Peat-Lite is due to the darker color of the media retaining more warmth during winter and spring cropping, then it would be possible to use this advantage via the manufacture of darker coloured STG mats. However it is likely that under warmer growing conditions and high light levels, that the darker colored Peat-Lite media may heat up to levels that would retard germination in many species.

 

Perlite has a consistent and serious problem with particle contamination of the crop and harvested product. At the high density microgreens seeds are sown at, the rapid development of the seedling canopy carries with it surface particles of lightweight perlite so that these granules remain sitting on top of the foliage as the seedlings develop. It was possible to settle down some of these particles with use of a heavy water spray or blast of air, however spraying microgreens seedlings with water is not advisable due to the increased disease risk this poses, particularly under high humidity conditions. Lower seed density may assist with prevention of this problem by allowing perlite particles to fall back down onto the seed bed between seedlings, however this will reduce yields per unit area of growing bed. The dislodgment of perlite particles by the microgreens crop also meant that the seed bed became uneven and harvesting had to be carried out at a higher level, above the base of the plants, to prevent excessive contamination with perlite particles. This will also have reduced harvestable yield. Perlite contamination was noted in all species harvested from this treatment, and although not severe, is not an ideal situation for this type of crop. Growers would be advised to use lower seed densities to try and prevent this contamination problem.

 

Particle contamination was generally not seen in the Peat-Lite and vermiculite treatments. These heavier media formed a compact and damp seed bed which was not dislodged by the large numbers of vigorous seedlings. However problems were found with irrigation of these media which have a high moisture holding capacity, became over saturated rapidly and drained slowly. Over-saturation of a seed bed can lead to problems with a lack of oxygen in the root zone, predisposing the plants to disease. The timing and volume of irrigation with these heavier media became critical to managing the crop and the irrigation system could not be run continuously as would be possible with perlite and STG. Grower skill would be required to determine the moisture status of these media and adjust the irrigation on a regular basis to prevent problems originating from over saturation of the seedling bed. The perlite media did not tend to become over saturated and drained well, however it had poor capillary action and did not wick up moisture from the base of the channel to the surface of the seed bed in the early stages of growth, necessitating the use of water sprays to keep the media surface moist during the first few days of establishment. Also, the high density of the seed and vigorous germination meant that the top layer of lighter perlite particles were lifted up slightly from the rest of the seed bed by the developing roots and shoots, this would have reduced the capillary action of the perlite media. Despite the dryer nature of the perlite surface, it developed some isolated disease outbreaks, as did the Peat-Lite and vermiculite treatments.

 

The Sure to Grow® Pad product was the most straightforward media to manage, both in terms of installation and crop removal, but also with regards to irrigation. The pad product retained sufficient moisture between irrigations to keep the germinating seed moist, while providing sufficient aeration for radicle growth. The pads drained well and made it difficult to over-water the crop in the wide channel NFT system used, at any stage of development. Furthermore, with the STG pads it is possible to easily view the developing root systems by lifting the pads back to expose the underside. This would allow growers to check for early root rot signs and to assess root health at any stage of development. The only disadvantage seen during this trial with the STG treatment was that the root zone could heat up rapidly during days with high radiation to levels higher than the ambient air temperature and that this could also warm the nutrient solution to levels above those optimal for seedling growth. While this was only noted in the afternoon of 1 – 2 days during this early spring period, it is likely to be a greater problem in crops grown in warmer climates and for summer cropping. This problem however could be alleviated relatively easily with use of shade cloth and nutrient solution cooling, as is becoming common for NFT lettuce and vegetable production in warm climates.

 

Disease outbreaks are relatively common in microgreens crops, particularly those grown under warm and humid conditions. The extremely high density these crops are sown at, the use of certain media and delicate stage of growth of the crop predispose the seedlings to a number of fungal and bacterial pathogens. Using NFT wide channel systems does have a major advantage in that the crop should not need over-head irrigation and hence the foliage can remain dry. Many foliar pathogens need damp foliage and/or high humidity levels to attack the crop, thus sub-surface irrigation can assist with disease prevention. However overly damp growing media, and the high humidity that exists within the canopy of microgeens also creates a disease risk. While sterilised water (heated to 80o C/176o F for 15 minutes), and channels were used during this trial, isolated disease outbreaks did occur in the Peat-Lite, vermiculite and perlite growing media. This resulted in the development of white and pink mycelium development and wet rots of the lower stem which progressed outwards and resulted in seedling collapse. Disease affected less than 5% of the total crop, but may have reduced yield in some treatments. The Sure to Grow® pads did not develop any mycelium growth or surface rots – some slight root browning was noted on the base of the mat in the Arugula crop in both plantings, but this did not seem to have reduced yields or plant quality and was most likely due to heat build-up on warm days. It is possible that despite perlite and vermiculite being considered to be `sterile’ media, that they, along with the peat may have had contamination with disease spores or that disease spores entered the crop in the usual way (on wind currents, as dust contamination or seed borne as all microgreens seeds are untreated with fungicides). It is also likely that the physical properties of the Sure to Grow® Pads, which did not over-saturate during irrigation assisted with disease prevention.

 

The STG mats were the only treatment which did not have any influence on the EC or pH of the hydroponic nutrient solution irrigated through the growing channels. The Peat-Lite treatment had the most significant effect and increased the EC of the nutrient solution from 0.5 mScm-1 to 3.2 mS cm-1 within 48 hours due to the leaching of the soluble salts contained in the Peat-Lite mix. The pH of the Peat-Lite solution also dropped from 5.8 to 5.5, which despite the presence of dolomite and gypsum in the Peat-Lite mix, would have been due to the acidification by peat. These effects however did not seem to have any visible negative influence on plant growth. Vermiculite and perlite did not change the EC of the nutrient solution, however they both increased the pH. Vermiculite increased the pH from 5.8 to 7.8 within 48 hours, while perlite increased pH to a lesser degree. These changes in EC and pH in the nutrient solution caused by the Peat-Lite, vermiculite and perlite would need to be monitored and adjusted by growers to ensure that mineral uptake is optimised. STG appears to be inert with regards to EC and pH, making solution management more straight forward.

 

Relative growth rates

Relative growth rate, expressed as both fresh and dry weight accumulation per day are an indication of how the media treatment influences plant biomass production and development. While fresh weight determines final yield, dry weight is the more important parameter as it determines factors such as shelf life and quality and is a factor of the efficiency of photosynthesis or assimilate production in the plant. Each of the 3 microgreens species appears to respond differently both to growing media and season. Slightly different growing conditions between planting 1 and planting 2 also appear to have interacted with growing media treatment when it comes to both relative growth rates and yields.

 

For Arugula in planting one fresh weight accumulation was the same in all treatments, with just the perlite treatment having lower dry weight accumulation. For planting two, the STG treatment had significantly higher fresh weight, however the dry weight was not different in any treatment.

 

For broccoli in planting one there was no difference in dry weight accumulation between treatments, however the perlite had significantly lower fresh weight. For planting two there was also no difference in dry weight accumulation between any treatment, however the STG and Peat-Lite had significantly higher fresh weight accumulation.

 

For red cabbage in planting one there was no difference in fresh weight accumulation between treatments, however the perlite had significantly lower dry weight. In planting two the Peat-Lite and STG treatments had significantly higher fresh weight, but there were no differences between treatments for dry weight accumulation

 

While it is difficult to claim any general trends from the relative growth rate data, it does appear that the perlite treatment most often had the lower fresh and dry weight values compared to the other treatments. Where treatment differences did exist it was often the Peat-Lite and STG with the greater fresh weight accumulation values, although this is not absolute for all planting dates and species. From this data it is obvious that growing media treatment is not the only, or perhaps even the most important factor affecting relative growth rate. It is the interaction of season, species and treatment which influenced crop growth and development over both planting dates. It could be concluded from this data that the physical properties of perlite are not as optimal for microgreens growth and development as that of the Peat-Lite and STG.

 

Yields

As with relative growth rates, yield differences are affected by planting date and species as well as by growing media and by the interaction of these variables. Yield differences in both planting dates for the Arugula are significantly different between treatments with the STG giving the highest yields in both plantings, followed closely by the Peat-Lite and vermiculite treatments. Perlite consistently had lower fresh weight yields at harvest which could be a combination of smaller plant size and the fact that the perlite crop could not be harvested right down at the base of the plant due to presence of many perlite particles which would have contaminated the harvested product. Cutting the perlite microgreens seedlings higher in the stem to avoid the perlite particles may have resulted in less yield from this treatment with all species.

 

In the red cabbage there were no significant differences in yield between treatments, although differences in red coloration and quality did exist.

 

In the broccoli, planting one had significant differences in fresh weight yield with the Peat-Lite having the greatest yield, followed by the STG and vermiculite treatments. In planting two, the perlite treatment was significantly reduced due to disease, while the STG treatment gave the highest yield.

 

From the yield data analysis it can be concluded that different microgreens species respond differently to the media treatments. STG favoured growth of Arugula, however both Peat-Lite and STG favoured broccoli, while media had no significant effect on yield in red cabbage. Perlite consistently produced the lowest yields in all species and planting dates and was the only treatment severely infected with disease.

 

The differences in yield between growing media treatments may be due to a number of reasons. Perlite did not have the high capillary action in the NFT channel systems that vermiculite and Peat-Lite demonstrated and the dryer surface of this media may have been responsible for the lower yields and smaller seedlings. Peat-Lite contains humic acids and possibly other organic growth promotant compounds which may have assisted development and yields. The STG mats provided an excellent physical environment for the seedling growth with good drainage and high aeration in the system used, all of which play a role in growth and yield.

 

 

Harvested quality

The productivity of microgreens crops should not just be assessed based on fresh weight yields. Plant quality and post harvest life are of equal or even greater importance as microgreens typically have a limited shelf life and can develop a number of post harvest problems. Plant quality is influenced by a number of factors including density, genetics, environmental conditions, root zone factors, nutrition, disease presence and growing media. High quality microgreens should be uniform in size and developmental stage, with good colour development which is dark and consistent in red types, with no yellowing or leaf spots and stems of a reasonable length, however not overly elongated. The presence of fungal or bacterial pathogens in the production channels at the time of harvest can carry over and cause rots in the harvested product. Plants which are overly tall, thin, light for size and succulent generally have a lower shelf life compared to those which are more compact.

 

Throughout the trial, the Peat-Lite plants appeared taller, lighter and `thinner’ than all other treatments with elongated stem sections which may be due to the presence of additional fertilisers in the Peat-Lite media or to a high water holding capacity of the media. The perlite seedlings consistently appeared smaller, shorter and darker which is indicative of a dryer media surface. The STG plants did not develop the tall elongation of the Peat-Lite plants, and were compact, but well developed with high levels of red coloration on the red cabbage. Stems appeared to be thicker on the STG plants despite this crop looking slightly smaller than the Peat-Lite seedlings. The vermiculite treatment was more prone to yellowing of the lower leaves before harvest and this may have been due to the higher pH this treatment caused in the nutrient solution.

 

Shelf life

An acceptable shelf life period is vital for microgreens which are still in the delicate seedling stage and highly prone to desiccation and tissue breakdown. The respiration rate is also high in harvested microgreens and post harvest problems can be common. Post harvest handling is crucial with microgreens and removal of field heat within 30 minutes of harvest and maintaining the cut product at or below 4.4 oC or 40 oF throughout the supply chain is recommended. The most common reasons for limited shelf life in many microgreens species are over succulence or high water content which leads to rapid wilting post harvest and/or yellowing due to a loss of chlorophyll. Fungal and bacterial pathogens can also cause wet rots which cause a rapid breakdown of leaf tissue inside the pack, even under refrigeration.

 

There were some trends evident in the shelf life assessment trial. Generally the vermiculite and perlite were most prone to developing post harvest rots and tissue breakdown. Vermiculite often had post harvest yellowing of the foliage and perlite was prone to wilting. The Peat-Lite also tended to develop coloration problems such as pale green/yellowing, loss of chlorophyll and some wilt problems. The STG consistently maintained the highest product quality through the assessment period, possibly because it had a high quality harvested product to start with and a lack of any disease present in the production system may have prevented further development of post harvest rots.

 

SUMMARY

While there appears to be many interactions between microgreens species, season and growing media treatment differences, the main findings are:

 

  1. Perlite consistently performed the poorest of all 4 media evaluated – in terms of yield, product quality, particle contamination issues and disease occurrence. Peat-Lite vermiculite and STG did not demonstrate any major contamination issues of the harvested product.

 

  1. Peat-Lite, vermiculite and perlite were prone to developing disease outbreaks under warm and humid growing conditions despite good hygiene and sterilized water used during production. STG treatments remained disease free during the course of this trial.

 

  1. Media treatment has a significant effect on plant quality and post harvest shelf life. Vermiculite and perlite developed post harvest rots and yellowing. Peat-Lite and STG produced the longest shelf life. STG produced seedlings which are more compact, less elongated then other treatments with a greater shelf life and fewer post harvest problems.

 

  1. Peat-Lite appeared to have a slight germination advantage which may be due to the presence of organic compounds contained in peat such as humic acids which may be beneficial as additives to STG systems during the early stages of germination. Peat-Lite significantly changed the EC of the nutrient solution flowing through the system. STG was the only media which had no influence on solution EC or pH.

 

  1. STG had a clear and significant advantage in the efficiency and management of NFT microgreens production systems including greatly reduced set up and removal times, ease of irrigation management, and effective control of root zone moisture levels.

 

It appears from this trial that different species of microgreens respond to the physical properties of growing media in different ways – in this trial Arugula was the species which significantly and consistently produced greater yields as well as higher product quality in STG.

 

Disclaimer: No responsibility is taken for the use or misuse of the data presented in this report or for sections of this report re published or re stated out of context. This report is Private and confidential and can be distributed by the named client only.

 

Appendix one – microgreens nutrient formulation

Standard complete, hydroponic nutrient formulation for micro green production in NFT channels. For use with distilled or RO water only.

 

Amount of fertiliser salts in grams dissolved in two 10 litre stock solution tanks. A one in 400 dilution rate with water will give an EC of 0.5 mS cm-1 and TDS of 350. Solution diluted with sufficient water to achieve the correct working strength EC. pH level 5.8 – 6.0.

 

PART A

Calcium nitrate 1252.4 g

Potassium nitrate 144.4 g

Iron chelate (13%) 50 g

 

PART B

Potassium Nitrate 144.4 g

Monopotassium phosphate 202.7 g

Magnesium sulphate 424.8 g

Manganese sulphate 8 g

Zinc sulphate 1.1 g

Boric acid/Solubor 3.9 g

Copper sulphate 0.3 g

Ammonium molybdate 0.103 g

 

A one in 100 dilution rate will give the following levels of elements:

 

N = 16.7 mMole/l 233ppm

P = 1.5 mMole/l 47 ppm

K = 4.3 mMole/l 167 ppm

Mg = 1.7 mMole/l 42 ppm

Ca = 6.3 mMole/l 250 ppm

S = 1.7 mMole/l 55 ppm

Fe = 6.50 ppm

Mn = 2.18 ppm

Zn = 0.30 ppm

B = 0.66 ppm

Cu = 0.07 ppm

Mo = 0.04 ppm

 

Appendix two – Cornell Peat-Lite Mix

 

Batch size = 75 litres

 

 

37.5 litres of peat moss

37.5 litres of horticulture grade vermiculite

 

613 g Dolomite

405 g Gypsum

102 g super phosphate

76.5 g potassium nitrate

3.2 g Iron chelate (13%)

10 g Trace elements

Wetting agent

 

REFERENCES

 

Raviv M., Wallach R., Silber A and Bar-Tal A., 2002. Substrates and their analysis. In `Hydroponic Production of Vegetables and Ornamentals. D Savvas and H Prassam (eds). Published by Embryo Publications, Athens, Greece.

Appendix Three

 

Crop Trial Photos

 

 

 

Wide NFT channels (Sure Grow channels, manufactured in Australia)

 

Planting 1 – 16 September

Above – Planting 1, 22 September

2008

 

 

Right – planting one

24 September 2008, Treatments from left to right – Perlite, vermiculite, STG and peat lite (2 channels each)

Above, broccoli seed germination on STG

treatment

 

 

Above top – STG red cabbage, below, perlite red cabbage showing perlite particles in canopy.

 

Perlite broccoli treatment showing perlite particles on top of leaf canopy.

 

 

 

Wheatgrass nearing harvest.

 

 

 

Planting 2 – 27 October 2008

 

Right – isolated disease outbreaks in

vermiculite treatment

 

Left – STG red

cabbage

development

 

 

 

 

 

 

 

 

 

 

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