Trays and sowing
Microgreens calculator
Pick a crop and your tray. You get how much seed to sow, whether to soak it, how long to keep it covered, when to harvest, and a sowing plan for a steady supply.
Seed for one 10 × 20 in tray
22.5–42 g 0.79–1.48 oz
1,290 cm² (200 in²), the tray size both charts use.
- Soak first?
- No
- Blackout (covered)
- 1–2 days
- Sowing to harvest
- 8–12 days
- Johnny’s trial (Daikon, Red Arrow, Hong Vit): 22.5–28.5 g per 1020 tray, harvested at 8–9.5 days
- Utah State Extension: 42 g per 1020 tray, no soak, covered 1–2 days, harvest at 8–12 days
Sowing plan: a tray every 4 days
Up to 3 trays growing at once.
| Tray | Sow | Uncover | Harvest |
|---|---|---|---|
| 1 | Day 1 | Day 2 – Day 3 | Day 9 – Day 13 |
| 2 | Day 5 | Day 6 – Day 7 | Day 13 – Day 17 |
| 3 | Day 9 | Day 10 – Day 11 | Day 17 – Day 21 |
| 4 | Day 13 | Day 14 – Day 15 | Day 21 – Day 25 |
| 5 | Day 17 | Day 18 – Day 19 | Day 25 – Day 29 |
| 6 | Day 21 | Day 22 – Day 23 | Day 29 – Day 33 |
Where the numbers come from
Two published charts give seed rates for a standard 10 × 20 in "1020" tray: averages from Johnny's Selected Seeds' trial, harvested at the first true leaf, and Utah State Extension's growing guidelines. Where both list a crop, the range runs from one to the other. Other trays scale by area, so a 10 × 10 in tray takes half. Johnny's notes that results vary with growing conditions, harvest stage and seed lot, and to sow fewer seeds if you want the plants to grow larger.
Blackout is Utah State's "covered time": a weighted second tray rests on the seed, then sits upside down above it, so roots push down before the lights go on. For a steady supply, sow a tray every few days; the plan shows how many trays grow at once.
Sources
- Johnny's Selected Seeds. Micro Greens Yield Trial 2017: Comparison Chart for 29 Popular Varieties: average seed per 1020 tray and days to maturity at the first true leaf, with the notes on seeding density.
- Johnny's Selected Seeds. Microgreens Production (slide deck): presoaking shoot seed for 12–24 hours.
- Beck S. Grow Your Own Microgreens. Utah State University Extension, 2025 (updated 2026), Table 1: seed per 1020 tray, presoak, covered time and time to harvest, plus temperatures and 18 hours of light.
- Stallknecht E. Calculating and Using Daily Light Integral (DLI). Virginia Cooperative Extension SPES-720NP, 2025: 9–12 mol/m²/day for microgreens.
Questions
Why do the two charts disagree?
Johnny's averaged what it sowed by eye in a trial and cut at the first true leaf; Utah State gives general guidelines. Start in the middle of the range, note how the tray turns out, and adjust.
Do I need to soak the seed?
Only the large seeds here: Utah State soaks pea for 6 hours and sunflower for 12, and Johnny's presoaks shoot seed for 12–24 hours. Neither chart calls for soaking the other crops.
What temperature and light do microgreens need?
Utah State keeps them at 74 °F (23.3 °C) while germinating, 72 °F (22.2 °C) with the lights on and 68 °F (20 °C) with them off, under 18 hours of light. Virginia Tech suggests a daily light integral of 9–12 mol/m²/day.