Hydroponic Microgreens: How to Grow Them Without Soil, Which System to Choose and How Aquaponics Compares
Can you grow microgreens hydroponically? Yes, and it is one of the simplest ways to grow them. Microgreens are harvested 7-14 days after sowing, so they do not need a complex system: a grow mat soaked with water in a tray, bottom watering and a grow light are enough at home. Commercial growers use the same idea on a larger scale, with ebb and flow trays that flood the whole tray from below on a timer. Because coco and cellulose mats contain no nutrients, a light dose of fertilizer after the blackout phase is part of the method.
In this guide we explain what hydroponics and aquaponics are, how hydroponic microgreens compare with soil-grown ones, which hydroponic systems suit microgreens and which do not, and how to set up a tray at home step by step. We also cover ebb and flow trays for larger farms, water, nutrients and pH, the most common problems, and whether aquaponics makes sense for microgreens. Everything you need for soil-free growing, from mats to trays, is in our microgreen growing mediums and microgreen trays.
Table of Contents
1. What are hydroponics and aquaponics?
Hydroponics and aquaponics are two ways of growing plants without soil. Both give the grower more control over water and nutrients than soil does, and both work indoors, in greenhouses and in vertical farms. They differ in where the nutrients come from: in hydroponics you add them to the water; in aquaponics fish produce them.
Hydroponics
Hydroponics is growing plants with their roots in water containing dissolved nutrients instead of in soil. The roots either hang in the nutrient solution or grow through an inert growing medium that holds water, such as coco fiber, hemp, cellulose or perlite. Because there is no soil to buffer the water, the grower controls exactly what the roots get, and also has to keep the pH and the nutrient level in the right range.
In this article we use the word the way microgreen growers do in practice. For microgreens, hydroponics does not have to mean pumps and pipes: a coco fiber or hemp mat in a tray, watered with water and a nutrient solution, is a hydroponic system too. This is the simplest set-up, and the one we describe step by step in section 5.
Aquaponics
Aquaponics combines hydroponics with fish farming (aquaculture) in one closed loop. Fish live in a tank, bacteria turn their waste (ammonia) into nitrate, and the plants use the nitrate as food, cleaning the water before it flows back to the fish. One input, fish feed, produces two harvests: fish and plants. The system has to keep three groups of organisms healthy at the same time, so water quality is a compromise between the needs of fish, plants and bacteria. Section 9 explains what that means for microgreens.
2. Can you grow microgreens hydroponically?
Yes. Microgreens are very well suited to hydroponics because of how short their life is. They are harvested when the first true leaves appear, usually 7-14 days after sowing, and in the first days they live mostly on the energy stored in the seed. They do not need deep roots, a large volume of medium or months of feeding, only a thin layer that stays evenly moist, light and a small amount of nutrients once they start growing under the lamp.
That is why a thin mat works so well for them. A mat a few millimeters thick holds a lot of water for its size (our CocoMat and HempMat hold up to 10 times their own weight), so it stays evenly moist between waterings; you still top it up as it starts to dry. The roots grow into the mat, the stems stand up straight, and at harvest you cut the greens just above the mat, with no soil on the leaves.
Popular microgreens for hydroponic growing include leafy greens such as lettuce, kale and arugula, herbs such as basil, cilantro and parsley, and brassicas such as radish, broccoli, kohlrabi and mustard. Large seeds such as peas and sunflower also grow on mats; they need a longer blackout of up to 4 days.
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How nutritious are microgreens? A study by the University of Maryland and the US Department of Agriculture measured vitamins and carotenoids in 25 commercially available microgreens and found that their cotyledon leaves had higher nutrient concentrations than the mature leaves of the same vegetables in the USDA database. No single variety led in everything: red cabbage had the most vitamin C, cilantro the most carotenoids, garnet amaranth the most vitamin K1 and green daikon radish the most vitamin E. The study did not compare growing methods, so it does not tell you whether mats or soil give more nutritious greens.
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3. Hydroponic or soil microgreens: pros and cons
Both methods grow good microgreens, and research shows that a fiber mat does not have to cost you yield. In a study at the University of Bari, rapini microgreens grown on mats made from recycled textile fibers and from jute and kenaf gave the same average yield as those grown in peat, about 1.5 kg per square meter, while a polyester mat (Sure to Grow) gave 13.1% less. The peat-grown greens contained twice as much nitrate, and E. coli was found only in the peat-grown samples. The authors concluded that the textile and jute-kenaf mats are a valid alternative to peat. The study tested rapini on those specific mats, not every mat on the market, but it shows that growing without soil does not have to mean a smaller harvest.
The table below compares the two methods for home and small commercial growing.
Mats give clean harvests, which matters when you sell microgreens, and at home they keep soil out of the kitchen. If you are deciding which mat or medium to use, our ultimate guide to growing media compares coco, hemp, cellulose, soil and the others in detail, and CocoMats: the secret ingredient for successful microgreens growth answers the most common questions about coco mats.
4. Which hydroponic system is best for microgreens?
For microgreens on mats, we recommend two systems: at home, a mat in a tray watered from below by hand; on a rack or a farm, ebb and flow trays that flood the trays from below on a timer. Other hydroponic systems exist, but not all of them make sense for a crop that grows for two weeks and is harvested as a dense carpet. The table shows the common ones and our view of how they fit microgreens grown on mats.
At home, bottom watering by hand does the job: there is no pump to break and no irrigation plumbing to buy. On a rack or in a farm, ebb and flow hydroponic trays water many trays at once from below on a timed cycle, which saves a lot of work. Ebb and flow differs from NFT, where the solution flows through channels all the time, and from DWC, where the roots stay in an aerated tank. Section 6 explains how to set it up.
5. How to grow hydroponic microgreens at home, step by step
This is the method we recommend to anyone starting with hydroponic microgreens. It needs no pump and no electricity apart from the grow light.
What you need:
- Two trays of the same model, one with drainage holes and one without, for example our "10x20" Extra Strength growing trays. The tray with holes sits inside the tray without holes. Do not combine different tray models, because their sizes may not match.
- A grow mat cut to the tray: for Extra Strength trays, a CocoMat of 27 x 53 cm. HempMats, cellulose pads and ReFibre also work.
- Microgreen seeds of the varieties you want, from our microgreens seeds.
- Fertilizer for microgreens, such as our Fertilizer A+B.
- A grow light if you grow indoors, such as our LED grow light for microgreens, and a timer.
- A spray bottle, and a cover or a second tray for the blackout.
- pH test strips or a simple pH meter to check your water (see section 7).
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Step by step:
- Soak the mat. Soak the mat thoroughly in warm water before sowing, then place it in the tray with holes, set inside the tray without holes.
- Sow. Spread the seeds evenly over the whole mat, using the sowing rate recommended for the variety, and mist them lightly. Sowing too densely raises the risk of mold.
- Blackout. Cover the tray, for example with a second tray placed on top, which also presses the seeds gently onto the mat, and keep it in the dark: usually 1-2 days for small seeds that germinate quickly, up to 4 days for large seeds such as peas and sunflower. Slow-germinating seeds such as basil may need only a gentle cover without a tray pressing on them, or no blackout at all in warm conditions, so check the seed packet. Move the tray under the light when most seeds have sprouted and the shoots are about 1-2 cm tall. Check the mat every day: even a short dry spell can delay germination, so mist it if it starts to dry. Read more about germination and blackout days.
- Light. Uncover the tray and move it under the grow light. We recommend 14-18 hours of light a day, with the lamp about 20-25 cm above the microgreens.
- Feed and water from below. Once the microgreens are under the light, water them from below: pour the solution into the lower tray so the mat soaks it up. When the mat has taken up what it can, pour off any water still standing in the lower tray: the mat should stay moist, not glossy with water. With our Fertilizer A+B, the first watering is with the part B solution and the next one with the part A solution (details in section 7); after that, water from below with clean water whenever the mat starts to dry. Bottom watering keeps the leaves dry and lowers the risk of mold; more in our guide on how to water microgreens.
- Harvest. Harvest when the first true leaves appear, usually 7-14 days after sowing. Cut with clean scissors or a sharp knife just above the mat.
- Clean up. Used CocoMats and HempMats are biodegradable and can go on the compost. Wash and disinfect the trays before the next crop, as described in how to clean a growing tray.
If you are still choosing trays, our guide to the top trays for microgreens compares the sizes and depths of all our trays.
6. Commercial scale: ebb and flow systems and racks
When you grow dozens of trays, watering each one by hand takes too long. An ebb and flow (flood and drain) tray solves this: it is a large, flat tray with channels that lead to a drainage point. A pump connected through a lead-through with a tap floods the tray with nutrient solution at programmed times; when the pump switches off, the solution drains back into the reservoir. The flooding and draining also refreshes the air around the roots. For microgreens on mats, keep the water no higher than 1 cm, so the roots are watered and the seeds do not soak. An overflow fitting protects against overflooding, and a circulating pump in the reservoir keeps the solution mixed. The same tray also works with drip irrigation or with manual watering, when you simply pour the solution into the tray.
You can place your microgreen trays with holes, with the mats inside, directly on the ebb and flow tray (without the solid trays you use for bottom watering at home, so the water can reach the mats), or lay mats or pads directly on it: our cellulose pads, for example, are made for ebb and flood tables and gutter systems. Our Ebb & Flow hydroponic trays are made from 3 mm thick, UV-resistant virgin plastic, and every tray comes with a sieve and an irrigation connector. All four sizes have an inner depth of 5.6 cm.
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Designing a space-efficient rack. A microgreens farm grows upwards, so plan the rack before you buy trays:
- Adjustable shelf heights, so you can fit different crops and leave room for taller varieties.
- A dedicated LED grow light above every shelf, for even growth on every level.
- Thin growing media made for microgreens, such as coco mats, hemp mats or cellulose pads. Selecting the right medium matters for seed density and water uptake. Bulky media such as clay pebbles take up space and are unnecessary for microgreens.
- Clear pathways: in a commercial grow room, we recommend at least 60 cm of walking space between racks.
Equipment for an automated system: a water pump and irrigation fittings to deliver water and nutrients, a reservoir, a timer, a pH meter and a nutrient (EC) meter to check the solution, a thermometer to keep growing conditions stable, and cleaning supplies, spare plumbing parts and nutrient solution kept close at hand. In our experience, the market for hydroponic microgreen equipment is still young and some complete systems are overpriced, so building part of the equipment yourself from standard components is completely fine.
7. Water, nutrients and pH
Do hydroponic microgreens need nutrients? In the first days, the seedlings live on the energy stored in the seed. Once they are under the light and growing fast, they need minerals, and a mat, unlike soil, does not contain any. Our A+B fertilizer instructions say that fertilizing is recommended for all small-seeded microgreens such as amaranth, broccoli and basil, and not required for large seeds such as peas and fava beans, unless they grow on coco: on coco fiber mats and coco coir, fertilizer is mandatory for every crop, because these media contain no nutrients.
How to feed microgreens with our Fertilizer A+B:
- Mix 1 g of part A with 1 liter of water in one container and 1 g of part B with 1 liter of water in another. Never mix parts A and B together in the same container.
- Start after the blackout, when the trays go under the light: water once with the part B solution, and the next time once with the part A solution.
- For most microgreens, one watering with B and one with A is enough. For longer-growing micro herbs, you can repeat B and A after a week under the light.
In an ebb and flow system, keep the same order: fill the reservoir with the part B solution for one flood, then empty it and fill it with the part A solution for the next. After that, flood with clean water. Never put both parts in the reservoir at the same time.
pH. Without soil, there is much less to buffer changes in the pH of the water, so it is worth checking it with test strips or a simple meter. The Oklahoma State University Extension recommends a nutrient solution pH of about 5.5 for soilless growing, so that the pH around the roots stays between 6 and 6.5, the range where nutrients are most available. For microgreens, aim for 5.5-6.5. If your tap water is very hard or very alkaline, have it tested before you build a larger system.
Water and temperature. Use clean water, keep the reservoir covered so algae do not grow in it, and keep the grow room at a stable temperature with good air movement. Warm, humid, still air encourages mold on microgreens.
8. Common problems and how to solve them
A hydroponic system needs regular attention. In a connected system, a small problem in one place can reach every tray quickly, so routine checks and early action save whole crops.
- Mold on the mat or stems. Usually caused by too much water on the surface, sowing too densely and still, humid air. Water from below, improve airflow and sow evenly. More in how to prevent mold on microgreens.
- Rotting roots and a sour smell. Water standing too long in the tray or poor drainage. In ebb and flow trays, keep the water no higher than 1 cm and let it drain fully between floods.
- Algae, slime and blocked fittings. Algae grow where water with nutrients is exposed to light, so keep the reservoir covered. Clean the reservoir, pipes and trays regularly to prevent slime and blocked lines, and use clean water and new or clean growing media for every crop.
- pH and nutrient swings. Check pH and nutrient levels regularly and adjust them; outside the right range, plants cannot use the nutrients you add.
- Pump failure or a power cut. In an ebb and flow system, the mats stop getting water when the pump stops; in deep water culture, where an air pump aerates the solution, the roots get less oxygen when it stops. The passive Kratky method needs no pump. A backup power source or a manual watering plan protects the crop.
- Heat and high humidity. Ventilation and air circulation keep temperature and humidity stable, in hydroponics and in every other kind of indoor growing.
- Disease spreading between trays. Remove affected trays straight away, so the problem does not spread through the shared water.
- Lack of experience. Microgreens, and especially microgreens aquaponics, are still a young field. Consulting experienced growers helps, but it can be expensive, so look for books, videos, articles and other microgreens enthusiasts to learn from.
9. Microgreens aquaponics: is it worth it?
For most microgreen growers, aquaponics is worth it only if you already keep fish or run an aquaponics system for other crops; if you are starting from scratch to grow microgreens, hydroponics on mats is simpler. In a microgreens aquaponics system, water circulates in a closed loop between the fish tank and the growing trays, and the fish waste, converted by bacteria, feeds the microgreens. It is a sustainable way to grow: the FAO describes aquaponics as extremely water-efficient, with no soil, no chemical fertilizers and little waste, producing two crops from one input, fish feed. Some nutrients, such as iron, potassium and calcium, may still need to be added.
The same FAO publication lists the drawbacks. Start-up costs are higher than for soil growing or hydroponics. You need to know how to care for fish, bacteria and plants. Their needs do not always match, so the water is kept at a compromise pH of 6-7 and a temperature of 18-30°C. Daily management is mandatory, the system depends on electricity, and a mistake can cause the whole system to collapse. You also cannot use pesticides on the plants or antibiotics on the fish.
For microgreens, our view is simple. Microgreens need very few nutrients in their short life, so the main advantage of aquaponics, nutrients recycled from the fish feed, matters less than for lettuce or tomatoes grown for months.
FAQ
Are hydroponic microgreens healthy?
Microgreens are nutrient-dense: in a study of 25 microgreens by the University of Maryland and the USDA, their cotyledon leaves had higher concentrations of vitamins and carotenoids than mature leaves. That study did not compare growing methods. On a mat, microgreens stay free of soil, which makes them easy to wash and serve.
Which is better for growing microgreens, hydroponic or soil?
We recommend hydroponic mats for most growers: they keep harvests clean and work with bottom watering and ebb and flow trays, and in a University of Bari study, rapini microgreens grown on the tested textile and jute-kenaf mats gave the same yield as those grown in peat. Soil and peat buffer pH and nutrient levels better, so they are more forgiving if you do not want to measure anything.
Do hydroponic microgreens need nutrients?
It depends on the crop and the medium. We recommend fertilizer for small-seeded microgreens once they are under the light: coco and cellulose mats contain no nutrients, so we recommend one watering with each part of our A+B fertilizer after the blackout. On other media, large seeds such as peas can do without it; on coco, fertilizer is needed for every crop.
What are the advantages and disadvantages of growing microgreens using hydroponics?
The advantages are clean harvests with no soil, full control over water and nutrients, easy automation with ebb and flow trays and a lower risk of soil-borne pests. The disadvantages are that you need to add fertilizer and check the pH, and that in an automated system, a mistake or a pump failure affects many trays at once.
What is the best hydroponic system for microgreens?
At home, a grow mat in a tray with holes set inside a tray without holes, watered from below. For a commercial rack, ebb and flow trays that flood the trays from below on a timer.
Can you grow microgreens in just water?
We grow microgreens on a thin mat or pad that stays wet, which gives the roots something to hold on to and keeps the stems upright. Large seeds such as peas can grow on water alone on media other than coco; for small-seeded microgreens, we recommend a light feed. Sprouts are the crop grown in water alone, and they are harvested after only 3-5 days.
What is the healthiest microgreen to grow?
There is no single winner. In the University of Maryland and USDA study of 25 microgreens, red cabbage had the most vitamin C, cilantro the most carotenoids, garnet amaranth the most vitamin K1 and green daikon radish the most vitamin E. Growing a mix of varieties gives you a wider range of nutrients.
Do microgreens regrow after cutting?
Most microgreens do not. Pea shoots are the main exception: cut above the first node, they may grow a second, weaker crop. Read more in which microgreens regrow after cutting.
Summary
Microgreens are one of the easiest crops to grow hydroponically. At home, all you need is a grow mat in a tray with holes set inside a tray without holes, bottom watering, a grow light running 14-18 hours a day and a light dose of fertilizer after the blackout. On a commercial rack, ebb and flow trays do the watering for you. Keep the pH at about 5.5-6.5, keep the water clean and the air moving, and harvest when the first true leaves appear. Aquaponics is a sustainable option, but if you only want to grow microgreens, it is more complex than you need. Mats, trays and fertilizer are in our supplies for growing microgreens.
Sources and Further Reading:
- Xiao Z., Lester G.E., Luo Y., Wang Q. (2012). Assessment of vitamin and carotenoid concentrations of emerging food products: edible microgreens. Journal of Agricultural and Food Chemistry 60(31): 7644-7651: nutrient content of 25 microgreens compared with mature leaves.
- Di Gioia F., De Bellis P., Mininni C., Santamaria P., Serio F. (2017). Physicochemical, agronomical and microbiological evaluation of alternative growing media for the production of rapini (Brassica rapa L.) microgreens. Journal of the Science of Food and Agriculture 97(4): 1212-1219: yield of microgreens on fiber mats compared with peat.
- Oklahoma State University Extension: Electrical Conductivity and pH Guide for Hydroponics: pH and EC of nutrient solutions in soilless growing.
- FAO: Small-scale aquaponic food production. Integrated fish and plant farming (Fisheries and Aquaculture Technical Paper 589): how aquaponics works, water quality, benefits and drawbacks.
- Kratky B.A. (2009), Three non-circulating hydroponic methods for growing lettuce, Acta Horticulturae 843: the passive Kratky method.
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