Microgreens are ready to cut about 10 to 14 days after sowing.
That is the range given by Illinois Extension, the University of Illinois’ public outreach service, whose blog posts, news release and handout are the basis for this page.
Its growing handout says 1 to 3 weeks, depending on how big you want the greens.
Either way, a tray sown this week can be on your plate in two to three weeks. It needs a shallow container, seeds, potting mix and a bright window.
Pick seeds, a tray and a mix
Many vegetables work as microgreens. Mustard, kale, endive, arugula, beets, radish, watercress, peas, cabbage, basil and most kinds of lettuce all do.
Radish, broccoli, kale and cress belong to the brassica (broccoli) family. They taste like the full-size plants, only slightly more delicate.
Skip tomatoes, eggplants and peppers. Illinois Extension says plants in the nightshade family should not be grown as microgreens, because their stems and foliage contain toxins.
Choose seeds that sprout well and have not been treated with chemicals or coatings.
For the container:
- A shallow tray with drainage holes. A plastic tray, a pie tin or a takeout container works if you add holes.
- A second container underneath. Use one without holes, to catch the water that drains out.
A tray depth of 1 to 2 inches is ideal if you want to save on potting mix. A basic potting mix is the easiest growing medium. Fill the tray with an inch or two of moistened mix.
Microgreens suit winter, one more way of tending plants indoors through winter.
Sow thickly
Microgreens are cut while the shoots are still young, so the seed goes down close together, about ¼ inch apart or less.
Amounts depend on seed size:
- Large seeds such as radish: 6 to 8 seeds per square inch, or 2 to 2.5 tablespoons on a standard 10 by 20 inch flat.
- Small to medium seeds such as brassica mixes: 0.5 to 1 tablespoon per flat. For small seeds, about 10 to 12 per square inch.
Use a lower seed density if you plan to grow on to the first true leaf stage. At that stage the leaves look like the ones the full-size plant will have.
Level the mix and tamp it lightly with a flat object, leaving about a half inch below the rim. Scatter the seed evenly, with attention to the edges. Then mist the seed and mix until evenly moist, not wet.
Cover the seed with a thin layer of mix. If you would rather not have mix stick to the leaves and make a mess, use a moistened paper towel or a humidity dome instead.
The first two weeks, in order
- Day 1: sow, mist and cover. Cover the tray with a clear lid or plastic wrap. The lid raises humidity and helps the seeds sprout.
- Every day until they sprout: look. Keep the mix moist, never soaked. Under a paper towel, lift a corner gently to check.
- When the towel lifts: uncover. Take off the towel and the lid. Do not worry if you pull a few seedlings out, since most are well established.
- After that: mist once or twice a day, as needed.
- Days 10 to 14: cut at the first true leaves. They are ready once the first set of true leaves has formed.
Roots that reach the soil push the towel up.
Light, warmth and watering from below
Microgreens need about six to eight hours of light a day for best growth. A sunny, south-facing window is preferred, with LED grow lights as the alternative. As little as 4 hours a day is the lowest figure given.
If the seedlings grow leggy, add a grow light.
Herbs can share the same sill, in a windowsill pot or a countertop herb kit.
Turn the tray as the seedlings lean toward the light, so all sides grow evenly.
Warmth has two figures:
- Sprouting: an ideal soil temperature of around 75°F. A lidded tray in a sunny window at room temperature should do the trick, and a heat mat is optional.
- Growing: microgreens grow best around 70°F. They tolerate down to 50°F, with slower growth.
Check the tray daily. Spray it once or twice a day, or water from below. To water from below, stand the container in a tray with a shallow layer of water, which it slowly takes up over several days.
Illinois Extension calls bottom watering the best way to keep microgreens dry and less open to disease.
The other rule is not to overwater. If the mix is evenly moist, wait until it starts to dry, which shows first around the outer edge.
Cutting, washing and storing
Use a knife, scissors or kitchen shears. Cut about ¼ to ½ inch above the soil line, holding a bunch of leaves in one hand. This is best done by an adult.
You can also take up the whole plant with its roots. Cut the whole tray at once or harvest as needed.
Wash them well. Submerge the greens in cold water and rinse thoroughly, which removes seed coats and leftover soil. A colander or salad spinner helps.
Eat them the same day, or bag them and keep them in the refrigerator for up to a week.
Sprouts are not microgreens
The two are easy to mix up.
Sprouts are germinated seeds, often grown in the dark, and the entire seedling is eaten. With microgreens, only the tops are eaten.
Illinois Extension says microgreens are safer to grow than sprouts, because they are harvested when the sprout risks are not present. They also grow in soil and sunlight, rather than from seeds rinsed in water.
It says that from the 2000s, raw sprouts became known as a risk for food-borne illnesses like salmonella and E. coli, and that many past sprout contaminations can be linked to seed sources or poor sterilization.
It still advises good growing practices: seeds from a reputable company, and pots sterilized with a 10 percent bleach solution.
After the first cut
Once a tray is completely cut, compost the remaining stems and soil.
Repeating the whole process every week gives a continuous supply, so start the next tray the same way.