How to Grow Microgreens Indoors, From Seed to First Harvest

Microgreens need a shallow tray with drainage holes, damp medium, seed sown thickly, a few days of darkness, then light, and they are ready about one to two weeks after the seeds emerge. Utah State University (USU) Extension and the LSU AgCenter publish step-by-step guides for home growers, and the routine below combines them.

1. What microgreens are

LSU AgCenter defines microgreens as young, immature edible seedlings, typically harvested seven to 14 days after germination, started mostly from vegetable and herb seeds. The key differences from a regular garden, according to LSU: microgreens are usually grown indoors or in a controlled environment, they are sown densely instead of spaced for mature size, and they are harvested at a juvenile stage.

2. Choosing seeds

USU suggests seeds labeled for microgreens, such as radish, broccoli, sunflower, or pea shoots. LSU adds that most vegetable species work, including brassicas (broccoli, cabbage, mustard, kale), legumes (peas, clover, beans), aromatic herbs (basil, dill, cilantro), and others like beets, sweet corn, sunflowers, and radish.

One family to skip: LSU says to avoid solanaceous crops such as tomatoes, eggplant, and peppers. Their foliage has many tiny hairs that affect mouthfeel, and they tend to build up solanine in their leaves, which can cause stomach upset if eaten in large amounts.

Use fresh, properly stored seed for even germination. LSU notes that with older seed, you may need to sow more densely to get the same effect.

3. Trays and growing medium

Both guides call for shallow trays with drainage holes. USU says a standard 1020 tray works well, and that repurposed pie tins or takeout trays are fine. LSU suggests produce clamshells, takeout containers, or cookie trays with holes added, and reminds you to sanitize reused containers before seeding.

For the medium, USU lists seed-starting mix, coconut coir, or a hydroponic grow mat. LSU describes soilless potting mix made mostly of peat moss, vermiculite, and perlite, and says soil depths of 1 to 4 inches are typical.

Moisten before you sow. USU's test for coir: squeeze a handful. Your hand should be wet, but no water should drip. LSU's version: when you squeeze, water should barely stream out. USU's method for a 1020 tray is to add 2 quarts of pre-moistened coir to a tray with drain holes, set it in a solid tray holding 2 cups of water for 30 minutes, then discard any water left in the bottom tray.

4. How much seed

USU's table gives seeding rates per 1020 tray, by weight. A selection:

If your tray is smaller than a 1020, scale by area. A tray with half the growing surface takes about half the seed, so roughly 21 g of radish instead of 42 g. A kitchen scale makes this easy.

5. The dark-then-light routine

USU's method starts in the dark:

1. Weigh the seed and spread it evenly over the moist medium.
2. Cover and weight it. Place another tray directly on the seeds with something flat and heavy, 2 to 5 pounds, on top. This keeps seeds in contact with the medium so roots push down instead of lifting the seed. Leave it for about half the covered time in the table.
3. Lift the weight, keep it dark. Turn the top tray over so it forms a cover without touching the seedlings. They begin to sprout and stretch a little.
4. Turn on the lights. USU says artificial lights give the most control and should be on a timer for 18 hours on, 6 hours off. A south-facing window can work, though USU notes winter days are short.

LSU adds that some microgreens can even be grown in a dark closet or drawer, and that corn and sunflower microgreens grown in the dark are often described as sweeter and more delicate.

Temperature and air. USU suggests about 74°F during germination, 72°F with lights on, and 68°F with lights off, plus constant gentle airflow from a small fan, especially near a sunny window. LSU says heat mats and humidity domes are optional. If you use a dome, check daily, because mold can develop quickly when airflow is restricted.

No fertilizer needed. LSU says the soilless medium does not need fertilizer before planting, and none is required later because the plants are harvested so young.

6. Harvest

USU says plants are ready as soon as you see the first true leaves, or sooner if you prefer. LSU describes the two popular stages as before and after the true leaf appears, with most microgreens ready 7 to 14 days after the seeds emerge. Seeds harvested at the earlier cotyledon stage can be sown more densely. Cut just above the medium with clean scissors.

7. Key takeaways

• Microgreens are dense-sown seedlings harvested in about one to two weeks, needing only a shallow tray with drainage.
• Use seeds like radish, broccoli, kale, pea, and sunflower; avoid tomato, pepper, and eggplant.
• Pre-moisten the medium until it is damp but not dripping, and weigh seed by tray size.
• Start covered and weighted in the dark, then give about 18 hours of light a day with gentle airflow.
• No fertilizer is needed; harvest at or just before the first true leaves.