Growing Microgreens and Baby Greens Indoors

Researchers at UMD and elsewhere have learned that microgreens are higher in vitamins and phytochemicals than their mature counterparts. The content of major and minor nutrients and bioactive compounds (mostly phenolics) varies greatly between crops and is affected by environmental factors: light intensity, potting mix (growing media) nutrient content, and harvested greens storage conditions. For example, a higher light intensity increases the plant’s phenolic compound content.

Additional microgreens advantages

• Fun and easy to grow, they are a good way to introduce kids to gardening.
• They have a quick turnaround of edible greens in small spaces.
• Microgreens can be expensive to buy, but you can grow them yourself for half the price.
• They are nutritious and versatile in the kitchen, with vivid colors, a tender texture, and intense flavor.

Two plant families are especially well-suited for microgreen use:

• Amaranth family (Amaranthaceae), which includes beets, Swiss chard, leafy amaranth, and magenta spreen
• Cabbage/mustard family (Brassicaceae), which includes kale, cabbage, radish, mustard, arugula, mizuna, and komatsuna

Cabbage family plants germinate and grow faster than the beet family plants. Cilantro and basil (both slow-growing) and peas, lettuce, onions, carrots, and lots of other herbs and vegetables can be grown for microgreens.

To grow microgreens, all you need are seeds, reusable food-grade containers or planting trays (also called “flats”), growing media, water, heat, and light for quick germination and growth.

Seeds

• Save money by buying non-hybrid seeds. Shop around and buy in bulk if possible, as long as the seeds will be sown within three years. Seeds sold in 1/32 ounce packets can cost 30 times more per seed than quarter-pound bags.
• Soaking certain seeds in water for 6 to 12 hours will speed up germination; these include pea, sunflower, corn, garbanzo bean (chickpea), beet, Swiss chard, cilantro, mung bean, and buckwheat.

Containers

• Use shallow containers for ease of harvest.
• Plastic food containers and standard greenhouse flats (10 inches wide by 20 inches long) work well, as well as special microgreens trays.
• A standard design for commercially-available microgreens trays is a set of two shallow plastic trays. One is divided into channels that run the length of the tray which holds potting mix and seeds; it has drainage holes. It is placed into the other tray, which has no drainage holes since it acts as a water reservoir. Careful watering is required to prevent saturation of the potting mix.
• You can grow microgreens hydroponically with single-use mats made from natural materials like hemp, wood fiber, coconut coir, bamboo, or jute. The pre-cut mats take the place of potting mix for the roots, and are sized to fit inside a standard greenhouse flat. Seeds germinate on top of the mat and send roots into the material. Reusable silicon mats are also available.

Growing media

Growing media has many alternate names, such as “potting soil,” “planting/potting mix,” and “container substrate.” Media should not be confused with true soil, which contains mineral components like sand, silt, or clay. Since container media does not contain soil (despite “potting soil” being a widely-used product label), they are categorized as “soilless.”

• Use any lightweight soilless mix in the container or tray. Soilless mixes usually contain several ingredients, such as sphagnum peat moss, coconut coir, vermiculite, perlite, rice hulls, pine bark, and compost.
• Save money by mixing high-quality, screened, plant-based compost in equal amounts (50:50) with commercial potting mix. Avoid using garden soil (taken from the ground); it’s too dense for growing microgreens and baby greens indoors in containers.
• Regardless of the media type used, no fertilizer is needed. Seeds contain the necessary nutrients for initial growth, and they are harvested before they run out.
• Screen and reuse growing media after harvest and any remaining roots dry out. Refresh in equal amounts (50:50) with new potting mix for the next sowing.

Seeds for microgreens are sown more densely than seeds planted for crops that will fully mature, because seedlings are harvested before crowding causes too many problems. Due to this quick turn-around, no thinning (removing excess seedlings to give plants space) is needed.

It can be difficult to see dark-colored seeds; practice sowing seeds evenly since you might not be able to see where they land on dark potting mix.

It’s best not to mix species because of varying germination and growth rates.

Sowing steps

1. Fill a shallow container or tray with moist soilless growing media to a depth of 1 to 1½ inches.
2. Sow seeds thickly and evenly by weight, by volume, or estimated by eye. Sample techniques:
   • Space seeds 3/16-inch to ¼-inch apart, or about 5 seeds per linear inch of media.
   • Broadcast seeds evenly over the media surface at a rate of about 1 tablespoon of seeds (about 10 to 15 grams) per greenhouse flat (10 inches by 20 inches). Depending on the size of the seed, a standard-sized tray (flat) can accommodate 1500 to 4500 seeds.
3. Gently press seeds onto the media with your hands or a block of wood.

As with outdoor plants, growing conditions are important for plant health and harvest potential for plants grown indoors. Key factors are light, temperature, moisture, and airflow.

Light

• Light from a sunny window may suffice in some cases, but microgreens generally grow best under grow lights. Fluorescent or LED grow lights can be used as the only light source or as a supplement to sunlight (to extend the length of the day). The total exposure to light from any source should be about 16 hours each day. How far to put the lights above the plants will depend on the fixture’s intensity, but 6 to 12 inches above the foliage is typical.
• Lettuce, arugula, mustards, and Asian greens will grow acceptably well in less-than-ideal levels of light.
• Use an outlet timer to program the on and off times for the light. Programming the lights to run at night can save money since electricity is priced lower. LED lights also use less energy (to produce the same amount of light) as fluorescent lights.
• The selection of a grow light doesn’t have to be complicated or expensive. If you want to learn more about the technical specifications used in grow light descriptions and packaging so you can make product comparisons, explore the Maryland Grows blog article An Introduction to Gardening Under Lights.

Temperature

• After sowing, cover the container with plastic or another container to trap warmth and humidity to speed up germination. Excluding light for a few days after germination (giving the seedlings a “blackout period”) will cause the stems to lengthen, making harvesting easier.
• Microgreens will germinate and grow well from 70 to 75°F. Cabbage family plants germinate rapidly (in about 36 hours) at 72°F.

Moisture

• Tap water is fine for watering. Mist the seeds for the first few days to keep the media surface moist, then water from the bottom (by placing a container or tray into a pan of water to absorb it through the drain holes) or from the top.
• Keep the growing media moist but not saturated.

Airflow

• Ensure good air circulation to discourage plant diseases. A gentle breeze from a nearby fan can keep air moving around the dense cluster of plants.
• Periodically vent any tray or container covers used to boost humidity so the extra moisture doesn’t encourage mold.

1. Cut the stems off just above the top of the media (the “soil line”) when the true leaves have expanded. Use clean, sharp scissors or a knife.
2. Rinse harvested microgreens with water, pat dry, and use right away or refrigerate for up to 10 days.
3. Wash and re-use the trays and containers. (The seedlings will not regrow.)
4. Plant the next batch of seeds in fresh growing media, or mix old and new growing media together in a 50:50 ratio before planting.

As an example of harvest potential, 1 tablespoon of arugula seeds sown in a 10-inch by 20-inch tray will produce about 8 to 12 cups of microgreens.

Culinary use

Fresh microgreens have a wide variety of uses: in wraps, paninis, and sandwiches; in soups; in omelets and frittatas; sprinkled on salads or burgers; incorporated into pesto or nutritional smoothies; as garnishes for grain and pulse (lentil/pea/bean) dishes; chopped in dips; as cocktail garnishes; or eaten raw by themselves.

You can grow baby greens year-round with supplemental light. Cut to harvest the plants when baby greens reach 4 to 6 inches tall. They will regrow and can be harvested 1 to 2 more times. Thin plants as they grow after germination to achieve about a 2-inch spacing between plants.

Additional Resources

Making ‘Superfoods’ Prove It | UMD microgreens research

Health Benefits and Safe Handling of Salad Greens | Colorado State University

The ABCs of Microgreens | Penn State Extension