Growing Microgreens

Many plants are grown as microgreens, including the types shown in Figure 1. Having a variety of options allows for creating mixes incorporating different colors, textures, and flavors. The potential for using microgreens in meals is endless. To name a few ideas, they can be used as a pizza topping, on tacos, in sandwiches, in salads, or the fillings of ravioli, pierogis, or empanadas.

Figure 1. Common types of microgreens

Amaranth, Chervil, Kale, Parsley, Anise, Cilantro, Kohlrabi, Purslane, Arugula, Collard, Lemon Balm, Radish, Basil, Cress, Marigold, Scallion, Beet, Daikon, Mizuna, Shiso, Cabbage, Dill, Mustard, Shungiku, Carrot, Fennel, Orach, Sorrel, Chard, Hon Tsai Tai, Pac Choi, Tatsoi

Microgreens have a short post-harvest life, which can create local demand and the potential to generate large profits if a market exists. Restaurants are the primary market, but microgreens are also available in grocery stores, farmers' markets, and as part of some Community Supported Agriculture (CSA) subscriptions. It is important to understand your market to develop a microgreens product that meets consumer preferences. Another factor to highlight in marketing efforts is that research has shown microgreens generally have higher concentrations of vitamins than the same plants grown to maturity.

Farmer Spotlight: At a conference in the mid-western U.S., we talked with a farmer about his microgreens. He markets them directly to consumers as convenience food. He packages microgreens in clamshells and tells consumers that they can easily take a handful to place on foods like sandwiches, hamburgers or tacos.

Many seed companies have sections devoted to microgreens, which is a good place to investigate options. Some commonly grown microgreens are listed in Figure 1. If you are new to microgreens, these may be good ones to start with. The seed is also available in ready-made mixtures like spicy and mild mixes, or you can make mixes yourself. If you prefer to select seed that is not sold specifically for microgreens, it is important to use organic or non-treated seed. It is best to avoid pesticide-treated seed because, for some microgreen species, the seed coat persists on the seedling and can be eaten.

For commercial sales, farmers commonly grow microgreens in protected structures like greenhouses and high tunnels. For personal use, gardeners can grow them on windowsills and decks. Over the past few years, we have been growing microgreens as part of the Hydroponics and Aquaponics course we co-teach at Pennsylvania State University. Students have been growing them in a greenhouse from August through May with supplemental lighting.

Farmer Spotlight: We visited with a Pennsylvania farmer who grows microgreens in a high tunnel. He also uses the high tunnel to produce his spring vegetable transplants. Once those are planted in the field, he starts growing a variety of microgreens in the tunnel to sell to restaurants and through the farm's vegetable subscription service.

Production time can be as little as seven and up to 21 days from seeding to harvest, depending on the environment they are grown in and the type of microgreen that is grown. The ideal soil temperatures for germinating microgreens are 60 to 75°F and air temperatures between 60 and 70°F. They are a low light crop (DLI below 20 mols/m2/day). Keep in mind microgreens will grow under less than ideal conditions because they only need a short growing period. Even though production time is short, microgreens are very labor-intensive, with most labor needed during planting and harvesting.

When planting most microgreens, sow seeds thickly. Seeding rates vary depending on germination rates, seed size, soil and air temperatures, and light in the growing environment. Generally, use lower rates in the summer than in winter and for larger seed compared to a smaller seed. The goal is to produce as many seedlings as possible to maximize production while avoiding plant stretching or disease.

Plant seeds based on weight, volume, or by eye. For the microgreens we have been growing, we have had success using 10 to 15 grams of seed per standard 12-inch x 20-inch 10-row seeding tray. You can determine how many grams fit in a tablespoon and use it to apply seed by volume. For example, one tablespoon of brassica seeds weigh about 11 to 12 grams. You can also plant the seed by eye. Johnny's Selected Seed Company recommends 6 to 8 large seeds per square inch of tray or 10 to 12 small seeds per square inch.

In the Pennsylvania State University Hydroponics and Aquaponics course, students plant 10 to 12 grams of microgreens seed per standard seeding tray. Photo: Elsa Sánchez, Penn State

Microgreens are commonly grown in 1020 (standard) greenhouse trays or 10- or 20-row seedling trays filled with soilless potting media. Broadcast seed evenly over the media. When seeding by hand, we have found that it is helpful to start at the edges of the tray and then seed the middle to help ensure complete and uniform coverage of the tray. A thin layer of soilless media or vermiculite can be placed over the broadcast seed. In our experience, this step promotes uniform moisture around the seed and results in more uniform stands of microgreens. You can reuse planting media; however, it is better to use new planting media for each production cycle to minimize the development of disease. Generally, select one type of microgreen for each tray—different microgreen types have different germination and growth rates. However, more than one type with similar growth rates can be grown in a single tray if desired. If you are creating a microgreens mixture, you can combine different types after harvesting.

Microgreens seeded in a 10-row seeding tray and covered with a thin layer of vermiculite. Photo: Elsa Sánchez, Penn State

You can also grow microgreens on seeding mats. One advantage of using seeding mats is that harvested microgreens are cleaner than when growing in potting soil. In class, we have used a seeding mat inside 11-inch long x 7¹⁄₈-inch wide x 5-inch tall vented clamshells, which were seeded with a mix of microgreens with similar growth rates. The result is containers of microgreens that you can sell without harvesting.

Microgreens are growing on a seeding mat in a vented clamshell. Photo: Elsa Sánchez, Penn State

Sub-irrigation, such as with ebb-and-flow systems, works well for watering microgreens trays. This type of irrigation system helps keep leaves and stems dry, which is important to avoid disease. If you are growing microgreens for home-use, trays can be placed in a tub with shallow water. Remove trays from the tub once the potting soil has been wetted.

Damping-off possibly caused by Rhizoctonia or Botrytis species in a microgreens tray. Photo: Elsa Sánchez, Penn State

Damping-off is the only disease or pest issue we have encountered in the Hydroponics and Aquaponics class. This disease is favored by warm, humid conditions. Little or no fertilizer is needed because the seedlings are not grown for very long before harvesting. If you do fertilize, using a solution with 50 to 100 ppm nitrogen is generally sufficient. We usually use a 100-ppm nitrogen solution made with 20-10-20 fertilizer in our Hydroponics and Aquaponics class. We have grown them successfully with clear water as well. However, these have sometimes shown iron deficiency symptoms.

When harvesting microgreens, cut the seedling stems, leaving the roots behind. We have averaged about 0.30 lb or 136 g/10 row seeding flat for the types we are growing. You can use sharp scissors or knives to harvest. You can also use electric knives or garden clippers. Students in the Hydroponics and Aquaponics course tested an electric garden clipper, and the harvest was much quicker. Still, cuts were less precise, and more plant tissue damage reduced post-harvest longevity of the harvested microgreens.

Farmer Spotlight: Farmers at two large grower conventions told us that using electric clippers and knives to harvest microgreens results in shorter post-harvest life compared to harvesting with scissors. This is because electric clippers and knives tend to tear stems. One farmer mentioned that he replaces the blade on his electric knife frequently. By doing this, he gets more precise cuts and prolongs the post-harvest of his microgreens while harvesting quicker.

When harvesting, take care to avoid getting bits of potting soil in the microgreens. They can be difficult to remove from the harvested product, and biting down on a piece of perlite is an unpleasant experience that could turn customers away from your microgreens. Washing microgreens before selling them decreases their post-harvest life. Notify consumers to wash their microgreens before eating them to extend the post-harvest life, if that is an option for your market.

Harvest is the most time-consuming part of the production process. In addition to the clamshell method mentioned here, you can sell microgreens in seeding trays to eliminate harvest costs. However, more space is needed for transportation compared to harvested microgreens.

Ideally, microgreens are taken to market immediately after harvest. When that is not possible, they can be stored in cold storage for short periods. Research shows that storing at 41°F in dark storage can increase shelf-life up to 10–14 days, compared to 2–4 days in ambient conditions. Keep relative humidity consistent and as high as possible. Changing temperatures can result in condensation, which can decrease post-harvest life.

Your market will determine price, quantity, and packaging, for example, in clamshells or plastic bags. We have seen microgreens selling for $1.75 for a ½ oz in a plastic bag through a direct market and $40 per pound in 14-gallon totes through a wholesale market.

Costs of Production

The following costs of production are based on the Hydroponics and Aquaponics course offered at Pennsylvania State University. Values are meant to provide an estimate of the costs of producing microgreens. Adjust values based on your situation.

Labor: Estimated based on students taking the Hydroponics and Aquaponics course

Estimated Yield

Yields per tray below are the average yields observed from 14 to 28 crop cycles during 2016-17. Microgreens were grown in a greenhouse without supplemental lighting using a seeding rate of 10-15g over a 2-week production cycle.