Growing Hydroponic Microgreens: The Next Food Revolution
Why Microgreens Are Taking Off
Microgreens are tiny edible plants, harvested at the peak of tenderness. They may be small but they deliver intense bursts of flavour and nutritional content. Microgreens have become more popular in recent years thanks to increases in supply and demand: they are being used more as a complement to cooking and they are also becoming a viable proposition for hydroponic farmers.
Most microgreens are easy to germinate with just five to ten days from seedling to harvest. Microgreens can be grown in as little as a few square inches making then ideal for home gardeners.
On a larger scale, microgreens make a profitable commercial crop, well-suited to soilless production methods and hydroponic systems to deliver a high-quality, clean and grit-free product- and of course hydroponics go hand in hand with container farming!
What are Microgreens?
Microgreens originated in California, where innovative chefs started using them in new dishes to incorporate color, flavour, texture and interest to dishes. Today microgreens are used worldwide as toppings, garnishes, flavorings in salads and feature in many up-market restaurants as well as best selling cookery books and are sold as a high-value product in and supermarkets.
Microgreens are smaller than a baby salad leaf and will usually have produced just two leaves after expansion of the seedling leaves or cotyledons. Because they are harvested very young, microgreen are grown at a high density to maximize yields from each crop.
A diverse range of plant species are grown as microgreens and needs have developed beyond just flavour or looks. Some are produced specifically for their healthy compounds and properties and these have found a niche market within the health food industry as well as being popular with home gardeners.
For example, wheatgrass has been grown for many years as a health supplement and can also be grown as a microgreen. Other plants such as flax, chia, broccoli, radish and red brassica are also very healthy.
What Microgreens Can I Grow?
Microgreens fall into four main categories:
• Shoots and tendrils: this includes pea shoots, sunflower and corn shoots. These are often used as garnishes, but they all have distinctive although mild flavor.
• Spicy greens: microgreens with a punch include cress, arugula, radish, and mustards.
• Micro herbs: typically these can be used as garnishes or decorative finishes to your plate, but are also known for their characteristic flavors. This category includes parsley, fennel, edible chrysanthemums, cilantro, basil, French sorrel, mint, dill, chives, onion and shisho (perilla).
• Tender greens: this group is very diverse with a huge range of flavors and. It includes favourites such as red cabbage, broccoli, spinach, corn salad, endive, chicory, celery, carrot and lettuce but also, tatsoi, mitzuna, amaranth, chard and kale.
If you’re thinking of building a shipping container farm, all the above can be grown with minimal worry.
The primary advantage for using hydroponics is that no granular growing medium needs to be used. Because you use a high sowing rate and plant a high density of microgreens you need to avoid small particles of substrate or soil which can end up in the plant. Since microgreens are not usually washed after harvest, this poses a risk of crunchy grit ending up in the food
Hydroponic microgreens are best produced on a thin mat or capillary pad that holds the seed in place and retains some moisture for germination. You can even use Paper towel, sheet of rockwool or burlap or even thin kitchen cloth can all be used to cheaply grow a clean, high-quality crop.
You should always start with seeds that have been specifically bred for sprout or microgreen production should be obtained, which means the seed will have a low percentage of non-plant matter, be well cleaned and will not have been treated with fungicides or other chemicals. Seed companies have also introduced a range of specific microgreen cultivars that are a great improvement on standard varieties.
This is especially important when buying seeds for pea, corn or spinach microgreens, as the seeds from these species are often coated with fungicide. Some microgreen varieties have seeds that are mucilaginous, meaning that once wetted, the seed forms a thick, gelatine-like layer that holds moisture.
Cress and basil are examples of mucilaginous seed and these seed types should not be pre-soaked before sowing. Larger seeds such as wheatgrass, corn and peas may be pre-soaked in warm water for 24 hours before sowing, although this step is not essential.
Advanced Hydroponic Microgreens
Hydroponic systems for microgreens can be as ordinary as a flat, hand-watered kitchen tray, simple enough for a child to grow cress.
Or they can be complex aeroponic or nutrient film systems with carefully controlled environments.For this reason microgreens have become a favourite with vertical farming systems like those used in shipping container farms.
The microgreen seed should then be weighed and sown onto the wetted surface as evenly as possible. Using a seed shaker can assist with this process, but note that each species requires a different sowing density
As soon as the seeds germinate, microgreens require light and nutrients to produce the highest quality product. Artificial lighting doesn’t need to be intense and these young seedlings produce well under propagation lamps provided the lamps don’t produce too much heat, which may burn the tender young foliage.
Once the cotyledons (seedling leaves) are visible and are 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 nutrients will be absorbed by the root system.
A general purpose vegetative or seedling nutrient formulation is usually sufficient for microgreen production, but wheatgrass has different nutritional requirements, including a higher EC level, for maximum harvest quality. EC levels are typically run at seedling strength for microgreens (0.5 – 1.0 mS cm -1), although they may be adjusted for season in a similar way to lettuce and herb crops.
There is some scope to manipulate growth of microgreens with use of EC – higher EC can be used to boost color development in red types during low winter light if necessary. Control of EC will also affect the shelf life of cut microgreens. Seedlings grown on dilute solutions or in media with a high water-holding capacity can develop softer tissue and a higher rate of water loss post-harvest than those that have received a higher EC and been slightly more hardened.
Nutrient solution needs to be applied regularly and carefully to developing microgreens to avoid flooding the microgreens and wetting the foliage, which encourages fungal diseases, and also to make sure fresh nutrient solution is flushed through the root zone, oxygenating and feeding the seedlings.
Most hydroponic systems use only intermittent application of nutrients, followed by a period of drainage with the growing surface holding sufficient moisture around the roots between watering.
Food Safety and Hygiene
As you may expect there are food safety requirements for microgreen production. Generally, high-quality, seed, used in a clean system at the correct temperature and moisture levels, will germinate properly with few problems.
However various fungal pathogens can develop and grow on sprouting seeds, especially in the humid atmosphere and high densities microgreens are grown in.
Disease can happen when old seeds are used or when temperatures are either too hot or cool. Over-watering also poses a risk as the seeds can rot before germination. The water supply needs to be good as water can carry human and plant pathogens that contaminate a crop, although the municipal water supply is usually sufficient for all but the most sensitive of crops.
Again, this is where the controlled environments of hydroponic container farming systems may come to the fore in allowing tight control of the water and temperature.
There is an increasing concern and more regulations these days relating to food safety so all commercial growers need to know the guidelines they must follow for fresh salad crops- check your local state regulations.
Care needs to be taken when the microgreens are finally harvested: microgreens need a good, clean portion of stem below the leaves, but should not be cut so low as to risk uprooting the growing base.
Clean, sharp scissors are suitable for cutting microgreens on a small scale, while larger growers use electric mechanical harvesters.
During warm growing weather, microgreens, just as with herbs and lettuce, are best harvested early in the day when the foliage is cool and not dried out from the days’ warmth. By preserving water the shelf life of the product is prolonged. Some microgreens may even be shipped to customers while still growing in their trays to allowing on site harvesting as required- popular with high end restaurants.
Solutions to Common Microgreen Problems
The most common problems in microgreen production are rot and disease caused by over watering or high humidity. Too much water in the growing medium or atmosphere around the plants encourage fungal and bacterial growth. This can be easily alleviated by light air movement by for example using a portable fans in small areas.
Another issue for over-mature microgreens is that they may become too tall and flop over, making harvesting extremely difficult. The solution is here is timing- not leaving crop too long to grow.
For the indoor gardener or container farm operator, microgreens are an ideal crop – fast, high yield and requiring just a few inches of well-lit space, they can be easily grown on a warm, sunny windowsill, or incorporated into a high-tech hydroponic vertical farm system.
Although there is a degree of skill required in growing microgreens at high densities and maintaining quality, the wide range of species, and their growing popularity makes them a great commercial proposition for hydroponic growers.
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