REFERENCE GUIDE

The Free Microgreen Seed Density Guide

Most growers starting a microgreen operation plant by feel for the first two months. They scoop a handful, spread it across a tray, and hope. This guide is the one piece of paper that fixes that.

The four tray sizes covered in this guide

Every density number below is keyed to one of four standard trays. If your tray is not on this list, measure the planting surface in square inches and use the math at the end to scale.

The 10x20 is the reference. Everything else in this guide is calculated as a fraction of the 10x20.

The two numbers that actually matter

There are really only two inputs that decide how many grams of seed you put in a tray.

1. The square inches of the tray (covered above).
2. The germination rate of the seed batch you are about to plant.

That is it. Everything else, the variety, the soil, the lighting, the room temperature, lives downstream of those two.

Why germination rate matters more than most growers realize

Germination rate is the percentage of seeds in a packet that will actually wake up, push out a root, and turn into a plant. The number is printed on the seed package tag if your supplier is worth buying from.

A seed batch at top-tier germination is a different product than a seed batch at low germination, even if the variety, the supplier, and the bag look identical. The same scoop will produce a dense, even, sellable tray with one batch and a patchy thin tray with the other.

This is why two growers using the exact same density chart can get two completely different trays. One of them has fresher, healthier seed.

We use a specific germination baseline inside the Grown Like A Pro app to do the math for you, so you can plug in your batch's actual germination rate and the app outputs your exact gram count. The baseline number is part of how we keep our system accurate. The point you need to take from this guide is that germination rate is the lever that decides whether your density chart works or fails.

Density baselines by variety (per 10x20 tray)

The numbers below are the same ones inside the Grown Like A Pro app's microgreen cheat sheet. Sixty-one varieties. Each row gives the recommended grams per standard 10x20 tray, whether to soak the seed before planting, how many days under weight (w) and without weight (u) for blackout, the typical harvest day, the watering frequency, and the bottom-water amount at maturity in ounces.

Scaling to other tray sizes

If you are not using a 10x20, multiply the baseline by the tray's share of a 10x20's surface area.

Math for any other tray: multiplier = your_tray_sq_in / 200. A 10x14 nursery flat (140 sq in) is 0.70 of a 10x20. Broccoli at 30 g x 0.70 equals 21 g.

Five mistakes that wreck a density chart

These come up in customer conversations more than anything else.

1. Trusting a number from the internet without checking the tray size. Every density chart you have ever read assumed 10x20 unless it said otherwise. If a chart says "30 g of broccoli per tray" and you put 30 g into a 5x5, you just put eight times the right amount in.
2. Skipping the pre-soak on seeds that need it. Peas, sunflower, wheatgrass, buckwheat, beets, cilantro. These crops need to wake up before they hit soil. If you do not pre-soak, the recommended density still gives you patchy germination because the seed coat slows them down.
3. Treating an old seed bag like a fresh one. Seed loses germination as it sits. A 14 month old broccoli bag is not the same product as the broccoli bag your supplier shipped last week, even if the supplier is the same. Test a small tray first if a batch is past 12 months.
4. Spreading unevenly because you eyeball it. A density number assumes the seed is spread across the whole tray. A pile on one side and a thin strip on the other side gives you a tray that looks half dead.
5. Ignoring the germination rate on the bag tag. This is the entire point of this guide.

What the app does that this guide cannot

This guide will get you started and will keep you within range. The app will get you precise.

• Plug in your tray size, your variety, and the actual germination rate from the seed bag tag, and the app gives you the gram count to plant.
• Save it to your inventory so the next time you plant that variety from that batch, you do not need to do the math again.
• The app tracks how many trays you can still plant from each open seed bag so you know when to reorder before you run out.
• The seed density calculator is one of 460+ features inside the app.

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