Getting the seed amount right is the single biggest factor in a good microgreens tray. Too little seed and you get a sparse, low-yield tray. Too much and the seedlings compete for space, trap moisture, stretch, fall over and go moldy. The chart below gives tested starting points for 14 popular crops, and the rest of this guide explains how to adjust them.
Rule of thumb
- Small seeds (brassicas): about 15–35 g per 10×20 tray.
- Large seeds (peas, sunflower, wheat): about 170–340 g per 10×20 tray.
- For smaller trays, scale by area: a 10×10 tray takes half; a 5×5 tray takes one-eighth.
- Start at the low end. Increase only if your stand looks thin.
Seed density chart
All amounts are dry seed weight for one standard 10 × 20 inch (“1020”) tray, about 200 square inches of growing surface.
| Crop | Seed per 10×20 tray | Soak | Days to harvest | Note |
|---|---|---|---|---|
| Radish | 25–35 g (0.9–1.2 oz) | Not needed | 7–12 | Fast, forgiving, peppery. |
| Broccoli | 18–25 g (0.6–0.9 oz) | Not needed | 8–12 | Mild; harvest before true leaves. |
| Kale | 15–22 g (0.5–0.8 oz) | Not needed | 8–12 | Mild and sweet. |
| Red cabbage | 18–25 g (0.6–0.9 oz) | Not needed | 8–14 | Purple stems; easy. |
| Kohlrabi | 18–25 g (0.6–0.9 oz) | Not needed | 8–12 | Purple stems, mild. |
| Mustard | 15–20 g (0.5–0.7 oz) | Do not soak | 8–12 | Seeds turn gel-like when wet. |
| Arugula | 10–15 g (0.4–0.5 oz) | Do not soak | 8–12 | Sow evenly; seeds clump when wet. |
| Amaranth | 8–12 g (0.3–0.4 oz) | Not needed | 10–14 | Tiny seeds; keep surface moist. |
| Basil | 7–10 g (0.2–0.4 oz) | Do not soak | 16–25 | Slow; sow dry on damp medium. |
| Cilantro (split seed) | 30–40 g (1.1–1.4 oz) | 4–8 hours (optional) | 16–21 | Slow, uneven germination. |
| Beet | 30–40 g (1.1–1.4 oz) | 4–12 hours (optional) | 12–18 | Seed caps cling; mist often. |
| Pea shoots | 225–280 g (7.9–9.9 oz) | 8–12 hours | 10–14 | Can give a second, smaller cut. |
| Sunflower (black oil) | 170–225 g (6.0–7.9 oz) | 8–12 hours | 8–12 | Use weight in blackout to drop hulls. |
| Wheatgrass | 250–340 g (8.8–12.0 oz) | 8–12 hours | 7–10 | Hard red wheat berries. |
Prefer not to do the math? The microgreens seed calculator scales these numbers to any tray size and number of trays.
Why the amounts vary so much between crops
The weight of seed you need depends on two things: how big each seed is and how much space each seedling needs.
- Seed size. A gram of radish contains around 70–100 seeds, while a gram of amaranth contains well over a thousand. A gram of peas contains only about 4–5 seeds. That is why pea shoots need ten times the weight of radish.
- Seedling size. Sunflower and pea seedlings are large and need room; amaranth and basil are tiny and can grow shoulder to shoulder.
As a quick visual check, small seeds should cover the surface in a single layer with gaps of about one seed-width between them. Large soaked seeds (peas, sunflower) can be spread so they touch, but never piled two deep.
How to scale for a different tray size
Seed amounts scale with the growing area. Measure the inside of your tray in inches, multiply length by width, and divide by 200:
Seed for your tray = seed for a 1020 tray × (length × width ÷ 200)
| Tray size | Area | Fraction of a 1020 tray | Radish seed (from 25–35 g) |
|---|---|---|---|
| 10 × 20 in | 200 sq in | 1 | 25–35 g |
| 10 × 10 in | 100 sq in | ½ | 12.5–17.5 g |
| 6 × 8 in | 48 sq in | about ¼ | 6–8.4 g |
| 5 × 5 in | 25 sq in | ⅛ | 3.1–4.4 g |
If your tray is measured in centimeters, multiply length × width in cm and divide by 1,290 (the area of a 1020 tray in square centimeters).
Weighing small amounts of seed
For small trays you are often weighing just a few grams. A kitchen scale that reads in 1 g steps is good enough for most crops; a cheap jewelry scale (0.1 g) is better for basil and amaranth. Once you have weighed the right amount for your tray, measure it with a spoon and note how many spoons it was. Next time you can skip the scale.
Signs you sowed too much or too little
| What you see | Likely cause | What to change next time |
|---|---|---|
| Seeds sitting on top of each other | Too much seed | Reduce by 20–25% |
| Mold or a sour smell in the middle of the tray | Too dense, poor airflow | Reduce seed and add a fan |
| Long, thin stems falling over | Too dense (and/or low light) | Reduce seed; see why microgreens fall over |
| Bare patches of medium visible at harvest | Too little seed, or poor germination | Increase by 10–20%, or check seed freshness |
| Thick stems, leaves spread wide | Slightly sparse — fine for flavor, lower yield | Increase a little if you want more weight |
Adjust for your seed’s germination rate
Seed lots differ. If your packet germinates at 95%, the chart numbers work as they are. If it is older and only 70% of seeds sprout, you need more seed to get the same stand — or, better, fresh seed.
To test germination, place 20 seeds on a damp paper towel, fold it, seal it in a bag and keep it at room temperature. Count the sprouted seeds after 3 days (5–7 days for basil and cilantro) and multiply by 5 to get a percentage. Then adjust:
Adjusted seed = chart amount × (90 ÷ your germination %)
So a lot with 75% germination needs about 1.2 times the chart amount. Below about 70%, replacing the seed usually gives a better tray. More on this in microgreens not germinating.
How many trays does a packet sow?
| Packet | Radish (30 g/tray) | Broccoli (20 g/tray) | Peas (250 g/tray) |
|---|---|---|---|
| 1 oz (28 g) | about 1 tray | about 1.4 trays | about ⅛ tray |
| 4 oz (113 g) | about 4 trays | about 5.6 trays | under ½ tray |
| 1 lb (454 g) | about 15 trays | about 22 trays | about 1.8 trays |
| 5 lb (2.27 kg) | — | — | about 9 trays |
This is why pea and sunflower seed is usually bought by the pound or kilo, while brassica seed comes in ounces.
Frequently asked questions
Do I weigh seeds before or after soaking?
Before. All amounts in our charts are dry weight. Soaked peas and sunflower seeds roughly double in weight.
Is it bad to sow microgreens too thick?
Yes. Over-sowing is the most common cause of mold, leggy stems and lower-quality trays. A slightly thinner stand nearly always gives a better result.
Can I use the same density for a hydroponic mat?
Yes, the amounts are similar. On bare mats, keeping the surface moist during germination matters even more. See growing microgreens without soil.
What does a “1020 tray” mean?
It is the industry name for a tray measuring about 10 × 20 inches. Most microgreen seed rates are quoted per 1020 tray.
