Last Updated on October 9, 2026

Microgreens Seed Density Chart: Seeds per 10×20 Tray

A 10×20 tray takes about 10 to 13 grams of small seed like broccoli, kale, cabbage or arugula (roughly one tablespoon), 22.5 to 28.5 grams of radish in Johnny’s Selected Seeds trial (up to 42 grams at Utah State University Extension), 48 grams of soaked sunflower and 150 grams of soaked pea. The small-seed numbers come from that same Johnny’s trial, and the sunflower and pea numbers are Utah State’s, which sows broccoli and kale heavier, at 28 grams. By count instead of weight, the trial sows 10 to 12 small seeds or 6 to 8 large seeds per square inch. A 10×20 tray is 200 square inches, so that works out to 2,000 to 2,400 small seeds or 1,200 to 1,600 large seeds per tray. The charts below give the rate, soak, dark time and days to harvest for each crop, with the source for every number.

Microgreens seed density chart for a 10×20 tray

Utah State University Extension publishes one complete set of numbers for a home grower using a 1020 tray, the standard 10×20 flat:

Ounces are grams divided by 28.35 and rounded. After the dark period, Utah State runs grow lights 18 hours on and 6 hours off, on a timer, for every crop in the chart.

More microgreens: seed density by crop

Johnny’s Selected Seeds ran a microgreens yield trial at its research farm in 2017. It seeded each 1020 flat by eye at least three times, weighed the seed used, and harvested every crop at the first true leaf. The trial was run for market growers, but the tray is the same one you use at home.

Grams, trays per ounce and days are the trial’s averages, rounded to the nearest half. Johnny’s calls them a starting place and says the values are imprecise. It also says to sow fewer seeds per flat if you want to grow the greens larger than the first true leaf.

Why the two charts disagree, and which to use

The two sources sow brassicas at very different rates. Johnny’s trial used 13 grams of broccoli and 10 of kale per tray, where Utah State’s chart calls for 28 grams of each, two to nearly three times as much. Basil is further apart still, at 5 to 6.5 grams in the trial versus 28 in the other.

Penn State Extension, growing microgreens in a greenhouse for a university class, lines up closer to the trial’s side, at 10 to 15 grams of seed per 12×20 tray. It also recommends lower rates for larger seed and in summer, and higher rates in winter.

A sensible way to use both charts: start near the trial’s rate for brassicas and herbs, and move toward Utah State’s if the mat looks thin. Johnny’s growing guide says the seed should be thick enough to cover the flat but not so thick it blocks air flow, since too dense a sowing sets the stage for disease. Write down what you sow and how the tray looks each time; that guide gives the same advice for your own trays.

No scale? Use a tablespoon or count

Penn State Extension says one tablespoon of brassica seed weighs about 11 to 12 grams. That puts a level tablespoon right around Johnny’s rate for broccoli, kale, cabbage and arugula in a 10×20 tray. For other seeds, weigh one tray’s worth once on a kitchen scale, see how many spoonfuls it fills, and measure by spoon after that.

Counting works too. Johnny’s sows seeds 1/8 to 1/4 inch apart: 10 to 12 per square inch for small seeds and 6 to 8 per square inch for medium and large seeds. Over a 200 square inch tray that is 2,000 to 2,400 small seeds or 1,200 to 1,600 larger ones. It adds that big multigerm seeds like beet, chard and cilantro tempt you to sow fewer, but they should still go 1/8 to 1/4 inch apart.

Other tray sizes: multiply by area

Seed rate scales with surface area. Divide your tray’s area in square inches by 200 (a 10×20 tray) and multiply the chart rate by that number. For a round container, the area is 3.14 times the radius times the radius.

Broccoli is the trial’s rate and pea is Utah State’s, which also says a shallow tray with drainage holes works best, and repurposed containers such as pie tins or takeout trays can be used too. The 8-inch round is 3.14 × 4 × 4, about 50.2 square inches.

Light needs for microgreens

Microgreens do not need much light. Penn State Extension calls them a low-light crop, with a DLI (daily light integral) below 20 mol per square meter per day. Run for Utah State’s 18 hours, a DLI of 20 works out to about 309 µmol per square meter per second at the tray, from 20 ÷ (18 × 0.0036). My DLI calculator works out any other combination of light reading and hours, and my grow light distance chart covers how far to hang the light above the tray.

The tray shows you when the light is wrong. Johnny’s says a light that is too weak or too far away makes the crop stretch and look washed out, and one that is too close can dry the crop quickly or make it look burnt. On a windowsill, Penn State says a south window gets more sun than a north one, and greens leaning toward the glass are short on light.

Temperature matters about as much as light. Utah State holds 74°F during germination, 72°F with the lights on and 68°F with them off. Johnny’s gives 65 to 75°F as a generally good range and says temperatures above 75°F can raise disease pressure and inhibit germination in some varieties.

Microgreens or sprouts?

Sprouts are the no-tray option. My sprouts post grows them in a sprouting jar or tray with no mix, rinsed and drained 2 to 3 times a day, and harvested at 1 to 2 inches long. Microgreens grow in a tray of mix under light and get cut above the roots.

Quick questions

How many microgreen seeds do you put in a 10×20 tray?

By weight, broccoli, kale, cabbage and arugula went in at 10 to 13 grams per 10×20 tray in a Johnny’s Selected Seeds trial, roughly one tablespoon. By count, Johnny’s sows 10 to 12 small seeds or 6 to 8 large seeds per square inch, which is 2,000 to 2,400 small seeds or 1,200 to 1,600 large seeds over the tray’s 200 square inches.

How much pea and sunflower seed per 10×20 tray?

Utah State University Extension sows 150 grams of pea (about 5.3 ounces) and 48 grams of sunflower (about 1.7 ounces) per 1020 tray, after soaking the pea 6 hours and the sunflower 12 hours.

Do microgreen seeds need to be soaked?

Most do not. In Utah State University Extension’s chart only pea and sunflower get a presoak, 6 and 12 hours. Johnny’s Selected Seeds soaks its pea and sunflower shoot seed for 8 hours and does not reuse the water.

How long do microgreens take to grow?

Radish, arugula, kale and broccoli are ready in about 6 to 14 days across the two charts on this page. Herbs are slower: Johnny’s Selected Seeds says herbs grown as microgreens mature in 16 to 25 days, and Utah State gives cilantro 21 to 28 days.

How many hours of light do microgreens need?

Utah State University Extension runs grow lights 18 hours on and 6 hours off once the trays come out of the dark. Penn State Extension calls microgreens a low-light crop, with a daily light integral below 20 mol per square meter per day.

Greens on the shelf now, beds in spring

The shelf and lights you use for microgreens can start your spring transplants later, in trays or soil blocks. Those start dates come from your last frost: my seed starting calendar counts the weeks back from it, and you can look up your frost dates by zip code. Plan My Garden is free to start: enter your zip code, draw your beds, pick kale, lettuce and everything else you want to grow, and it places each plant at square-foot spacing and builds a planting schedule (start indoors, transplant and direct sow dates) from your frost dates.

Related: DLI Calculator · Growing Sprouts Indoors All Winter · Vegetable Seed Germination Temperature Chart · Seed Viability Chart