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Microgreens seed density per tray

Extension charts do not all use the same tray. Read the tray size before you copy a gram number.

By Ryan Moalemi. Updated November 9, 2026.

Seed density is the amount of seed you put on a known area of tray. For home microgreens, the useful version of that number is grams for the tray in front of you. Extension publications do publish gram figures, and they do not all describe the same tray. Copy a number only after you match the tray size printed next to it. The seed calculator on this site scales one set of those figures by area. It does not replace the other published methods, and it does not claim a single correct rate.

Three published ways to say "how much seed"

Utah State University Extension prints grams per 1020 tray for individual crops. A 1020 is the nominal 10 by 20 inch flat, 200 square inches if you take the name literally. Radish is 42 grams, pea is 150 grams, sunflower is 48 grams, arugula is 10 grams, and broccoli, kale, basil, and cilantro are 28 grams in that table. Those are single starting values, not ranges, and they are tied to that tray.

University of Maryland Extension gives a sample broadcast for a 10 by 20 inch greenhouse flat: about 1 tablespoon, described as about 10 to 15 grams. Depending on seed size, that flat holds about 1,500 to 4,500 seeds. Maryland also offers a spacing sample, about 3/16 to 1/4 inch apart, or about 5 seeds per linear inch. The tablespoon band is not a separate weighed rate for every crop. It is one technique. This site uses it only where Utah State did not publish a crop gram rate, and the calculator shows it as 10 to 15 grams, not as a false single number.

Penn State Extension, in the Sánchez and Berghage article, reports success with 10 to 15 grams per standard 12 by 20 inch 10-row seeding tray. That tray is 240 square inches, larger than a 1020. Students in that program planted about 10 to 12 grams per standard seeding tray. The same article says one tablespoon of brassica seed weighs about 11 to 12 grams, which sits inside Maryland's 10 to 15 gram description of a tablespoon and shows why a spoon is only a rough scale. Penn State also relays a count target used by a commercial seed supplier: about 6 to 8 large seeds per square inch, or about 10 to 12 small seeds per square inch. The supplier is not named here. The count is the part that travels to any tray size, because it is already "per square inch."

Read those side by side and the conflict is obvious. Broccoli at 28 grams on 200 square inches (Utah State) is a much heavier sowing than 10 to 15 grams on 240 square inches (Penn State). Both are published. Penn State also says to use lower rates in summer than in winter, and lower rates for larger seed than for smaller seed. In context of the per-square-inch counts, "lower" for large seed means fewer seeds on the area, not automatically fewer grams. Pea still weighs more per tray than arugula because each seed is heavy. Utah State's 150 gram pea rate and 10 gram arugula rate are the illustration.

Grams for a nominal 10 by 20 inch tray

Use this table with the tray size in the header. Do not paste these grams onto a 12 by 20 inch flat and call them the Penn State rate. The Penn State band is the paragraph above.

Mississippi State University Extension gives volume, not grams, for two examples on a 10 by 20 inch tray: about 2 to 3 teaspoons of red cabbage seed, and about 2 to 3 tablespoons of radish seed. A tablespoon of radish is not the same weight as a tablespoon of mustard. Maryland's own seed-count table shows why. It lists about 53 beet seeds per gram and about 800 per tablespoon, about 281 broccoli seeds per gram and about 3,000 per tablespoon, and about 530 mustard seeds per gram and about 6,500 per tablespoon. A spoon measure changes its gram weight when the seed changes. A scale removes that guess. If you only have spoons, calibrate once: weigh one level tablespoon of the seed you actually have, then reuse that weight.

How to scale to a smaller tray

Divide the small tray's area by 200, then multiply the 10 by 20 inch gram rate by that fraction. A 10 by 10 inch tray is 100 square inches, half of 200, so it gets half the seed. A 5 by 5 inch tray is 25 square inches, one eighth. A takeout container that measures 4 by 8 inches on the inside is 32 square inches, which is 32/200, or 0.16, times the reference rate. For arugula at 10 grams, that is about 1.6 grams. For pea at 150 grams, it is about 24 grams. Measure the inside floor, not the outside rim.

Illinois Extension prints spoon amounts for small containers: about 1 tablespoon of large seed or 1 teaspoon of small seed in a 3 by 6 inch container, double that for 4 by 8 inches, and about 1 and 1/3 tablespoons or teaspoons for a 5 inch round pot. Those spoons will not match the area scale seed for seed. Pick one method and write down what you sowed. Penn State's per-square-inch count is the other scaler: about 10 to 12 small seeds or 6 to 8 large seeds. Turning that count into grams needs the weight of your own seed lot. Maryland's seeds-per-gram examples cover beet, broccoli, and mustard only.

Germination is the adjustment this calculator skips. If a packet germinates poorly, the same gram rate produces a thinner stand. Penn State's downloadable seed density calculator can take germinability into account. Francesco Di Gioia describes it as using average seed weight from earlier measurements, with the warning that seed weight still varies by batch. Use it when you want that correction. Use a kitchen scale either way.

Even beats heavy

Penn State says to sow the edges first, then the middle, so the rate is actually spread. Press seed onto moist mix. Di Gioia often leaves seed uncovered so the cut greens stay clean. Sánchez and Berghage say a thin cover of mix or vermiculite gave their class a more even stand. Either finish is published. If a tray smells sour, sow the next one lighter. If you see bare mix and wanted a carpet, sow the next one a step heavier.

Soak changes handling, not the area math

Weigh pea and sunflower dry, then soak. Utah State lists about 6 hours for pea and 12 for sunflower. Maryland's 6 to 12 hour list also includes beet, chard, and cilantro, while Utah State marks cilantro as no presoak. Keep the gram rate the same either way. Wet seed is not a reason to sow extra.

For a crop-to-crop reading of the two weights people compare most often, see pea versus radish. For how a heavy rate changes the seed bill, see kit versus DIY cost.

FAQ

Sources

• Stephen Beck, Grow Your Own Microgreens, Utah State University Extension, updated January 2026.
• Jon Traunfeld, Growing Microgreens and Baby Greens Indoors, University of Maryland Extension, revised March 2026.
• Elsa Sánchez and Robert Berghage, Growing Microgreens, Penn State Extension, updated December 16, 2025.
• Francesco Di Gioia, A Step-By-Step Guide for Growing Microgreens at Home, Penn State Extension, updated September 20, 2026.
• Francesco Di Gioia, Microgreens Seed Density Calculator, Penn State Extension.
• Gary R. Bachman, Growing Microgreens for the Mississippi Gardener, Mississippi State University Extension, publication 2857.
• Microgreens: year-round edible greens to grow at home, University of Illinois Extension, Kane County Master Gardeners.

Related guides

• Microgreens seed calculator

  Scale a published 10 by 20 inch rate to your tray and estimate seed cost.

• Pea shoots vs radish microgreens

  Radish is a light sowing of a spicy green. Pea is a heavy sowing of a milder shoot.

• How to grow microgreens in a small apartment

  A tray, a soilless mix, and a bright spot are enough to start. Here is the sequence extension publications describe.

• Microgreens kit vs DIY: what the costs are made of

  The tray is a one-time purchase. Seed is the cost that returns with every sowing.