Broccoli goes from dry seed to a cut tray in 8 to 12 days. No soaking, no lights you have to buy, no second attempt if you get the first one right. It is the crop we hand to people who have never grown anything.
We run around 400 trays a week across more than 20 varieties on our farm in Belgrade, and broccoli is one of the few where every mistake sits in the last three days rather than the first three. Cut it too early and you lose a third of the weight. Cut it too late and the flavor turns sharp.
Here is what this guide gives you:
- The sowing weight, the days under weight, and the day to cut
- How to tell root hairs from mold on day 3, which is the question that ends most first trays
- What sulforaphane actually is, why it only appears when you chew, and what the research says
Quick facts
| Question | Answer |
|---|---|
| Days to first cut | 8 to 12 |
| Soak before sowing | None. Broccoli sows dry. |
| Days in blackout, under weight | 2 to 4 |
| Seed per 10x20 tray | 17 to 20 g, the industry-standard rate |
| Yield per 10x20 tray | 250 to 350 g, general figure |
| Difficulty | Low. One of the crops we tell beginners to start with. |
| Taste | Mild cabbage with a light pepper finish. Much softer than radish. |
| Fridge life after cutting | 7 to 10 days grown at home. Our cut and packed trays hold 8 to 14. |
| Grows back after cutting | No. One cut per tray. |
Why people grow broccoli on purpose
Most crops go into a tray for texture or color. Broccoli goes in for one compound.
Broccoli seedlings carry glucoraphanin, which does nothing on its own. It sits in one part of the cell and an enzyme called myrosinase sits in another, and they only meet when the tissue is broken. Chewing, chopping or blending breaks it. That reaction is what produces sulforaphane.
Two research findings are worth knowing before you sow anything:
- Fahey, Zhang and Talalay measured 3-day-old broccoli seedlings and found glucoraphanin at many times the concentration in the mature head, gram for gram (PNAS, 1997).
- Xiao and colleagues measured 25 microgreen varieties and found vitamin C, vitamin E, vitamin K and carotenoid concentrations generally higher in the seedling than in the mature leaf of the same plant (Journal of Agricultural and Food Chemistry, 2012).
What follows from the chemistry is a kitchen instruction - heat destroys myrosinase. A tray cooked into a hot pan gives you a fraction of what the same tray gives you chopped raw. That is the kitchen section below, and it is the part most people skip.
Broccoli microgreens or broccoli sprouts
Same seed, two stopping points. Sprouts stay in the dark in water and get eaten whole, root and all, on day 3 or 4. Broccoli microgreens spend two to four days in the dark, then grow under light until day 8 to 12, and get cut above the medium so nothing but leaf and stem reaches the plate.
The short version: sprouts are faster and cheaper per gram, microgreens taste better, keep longer and carry the leaf the plant only makes under light. We wrote the long version, including where sprouts genuinely win, in microgreens vs sprouts.
What you need
- Seed. Any broccoli variety works. Waltham 29 and Di Cicco are the two we see most often on seed lists. Buy seed sold for sprouting or microgreens, which is tested for pathogens.
- Two 10x20 trays, one with holes and one without. The solid one holds the water.
- Medium. Coconut coir, a peat and coir mix, or a hemp mat. Coir drains well and is what we run.
- A weight. A second tray with 2 to 4 kg on top of it. A few books work.
- A spray bottle for the first three days.
- Light. A bright window works. A cheap LED shop light works better and gives you an even tray.
You do not need a heat mat, a fan or a pH meter for broccoli. Those matter on crops that mold easily. Broccoli is not one of them.
Sowing to cut, day by day
| Day | What you do | What you should see |
|---|---|---|
| 0 | Fill the holed tray with 3 to 4 cm of damp coir, level it, scatter the seed evenly, mist, cover with the second tray and add the weight. | Seed sits in one even layer, not stacked. Broccoli is small, so a heavy hand shows up on day 6. |
| 1 to 2 | Leave the weight on. Lift once a day, mist, put it back. | White root hairs at the base, seed coats splitting, no green. |
| 3 | Take the weight off, keep the tray covered and dark for one more day if the mat is uneven. | Pale yellow stems, 2 to 3 cm, pushing against the lid. |
| 4 | Lights on. Move to bottom watering: pour water into the solid tray and let the roots drink it up. | Stems straighten and green within hours. |
| 5 to 7 | Water from the bottom once a day, roughly 250 to 500 ml for a 10x20 tray. Never over the leaf. | Cotyledons open flat and turn a full green. Seed coats start to drop. |
| 8 to 12 | Cut with a clean knife or scissors, above the medium. | A 5 to 8 cm stand, cotyledons wide open, the first true leaf just showing on the earliest plants. |
The blackout window is what makes the stems reach and gives you the height. Take the weight off too early and you get a short, uneven tray that is hard to cut.
Root hairs or mold: the day-3 question
More first trays get thrown out on day 3 than fail for any other reason, and almost always by mistake. Broccoli grows dense white root hairs earlier than most crops, and they look exactly like what people expect mold to look like.
Five things separate them, and you only need one:
| Look at | Root hairs | Mold |
|---|---|---|
| Where it sits | Only at the base, where stem meets medium | Climbs the stem, sits on seed coats, spreads upward |
| How it is spread | Evenly across the whole tray | In patches, spreading out from one point |
| Color | Bright white, hair fine | Gray or blue-tinged, cobweb-like |
| Smell | Nothing, or clean soil | Sour, musty |
| Mist test | Collapses flat and disappears | Stays exactly as it was |
The mist test settles it in ten seconds. Spray the patch. Root hairs lie down and vanish into the stem. Mold does not care.
The other three things that go wrong
| What you see | What caused it | What to do |
|---|---|---|
| Tall, pale, falling over | Too little light after day 4, or the tray sat in blackout past day 4 | Move closer to the light. Broccoli stretches fast and does not recover its color once the stem has run. |
| Patchy tray, bare spots | Uneven sowing, or the weight was too light so some seed never made contact | Nothing saves this tray. Next time level the medium with a straight edge and use the full 2 to 4 kg. |
| Yellow leaves after day 6 | Still in the dark, or watering from the top and drowning the crown | Bottom water only from day 4. Yellow greens up again within a day under light. |
When to cut: flavor against yield
This is the only real decision in the cycle, and no guide we have read tells you how to make it.
Broccoli keeps adding weight until the true leaves come in, and it keeps getting sharper at the same time. Day 8 gives you the sweetest, mildest tray and the smallest one. Day 12 gives you noticeably more grams.
We cut for the plate, not the scale, so we stay inside that window, between day 8 and day 12. If you are growing to fill a box for the week, take the later day and expect a stronger taste. Cut the whole tray at once either way. A half-cut tray dries out at the edges and never catches up.
Keeping them for a week and a half
Cutting is not what decides shelf life. What you do in the next twenty minutes is.
- Cut dry. A wet tray at cutting is the single most common reason microgreens turn to slime in the fridge.
- Do not wash, unless you have to. Water on the leaf shortens the life of the whole batch.
- Get it cold fast. Into a container, into the fridge, within twenty minutes of the cut.
- Line the container with a dry paper towel and close it. The towel takes the moisture the leaf gives off.
Done that way, a home tray holds 7 to 10 days. Our own cut and packed trays hold 8 to 14, which is what the cold chain buys you and the reason our boxes reach a customer on Saturday having been cut on Friday.
In the kitchen: chop, wait, then eat
Broccoli microgreens taste like a mild young cabbage with a pepper finish that arrives late. They go where you would put a lettuce leaf, not where you would put a herb.
Three rules, and the first one is the one that matters:
- Chop, then wait. Cutting the tissue starts the myrosinase reaction. Give it a few minutes on the board before it goes on the plate. Fahey and colleagues showed that bioavailability depends on that enzyme being active (PLOS ONE, 2015).
- Raw wherever possible. Heat destroys the enzyme. Add them to a warm dish after it comes off the heat, not while it is cooking.
- A handful, not a garnish. Three sprigs on a plate is decoration. A full handful in a sandwich or a bowl is food, and it is the amount the numbers above were measured at.
They work in a sandwich, on eggs, folded into a grain bowl, and blended into a smoothie where the pepper finish disappears completely. If you want the same plant without a tray with soil in the kitchen, our dried microgreens seasoning is the shelf-stable version and goes on top of a finished dish.
Frequently asked questions
Do broccoli microgreens grow back after cutting?
No. The growing point is above the cut, so once it is gone the plant is done. Compost the medium and sow again. This is true of every microgreen except pea shoots, which will sometimes give a weak second cut.
Do I need to soak the seed?
No. Broccoli is small enough that it takes up water from the medium in a few hours. Soaking small brassica seed makes it clump and sow unevenly.
More sulforaphane in microgreens or in sprouts?
The measured research on very high glucoraphanin concentrations was done on 3-day-old sprouts (PNAS, 1997), not on 10-day microgreens, and the concentration falls as the plant grows. What you gain in the tray is taste, shelf life and microgreens you will actually eat every day.
How much is a normal amount to eat?
There is no established portion for microgreens. A handful, most days, in place of a lettuce leaf, is how we eat them ourselves.
Why do my trays smell sour?
Standing water in the bottom tray. Pour off whatever the roots have not taken up within an hour of watering.
Can I use potting soil?
Yes, but coir is cleaner to cut over and does not bring fungus gnats into a kitchen.
Get the crop sheet
Broccoli is one crop. The soak time, blackout days, sowing weight and cut day are different for every one of the twenty we grow, and that is the part nobody remembers.
We put all of them on one printable page: soak, blackout, harvest day, seeding density and expected yield per tray, for 20+ crops, from our own growing schedule. It is free and it arrives as a PDF.
The Microgreens Cheat Sheet goes live on September 9, 2026. The download link appears here that day.
Sources
- Fahey, J. W., Zhang, Y., Talalay, P. (1997). Broccoli sprouts: an exceptionally rich source of inducers of enzymes that protect against chemical carcinogens. Proceedings of the National Academy of Sciences, 94(19), 10367-10372. doi:10.1073/pnas.94.19.10367
- Xiao, Z., Lester, G. E., Luo, Y., Wang, Q. (2012). Assessment of vitamin and carotenoid concentrations of emerging food products: edible microgreens. Journal of Agricultural and Food Chemistry, 60(31), 7644-7651. doi:10.1021/jf300459b
- Fahey, J. W. et al. (2015). Sulforaphane bioavailability from glucoraphanin-rich broccoli: control by active endogenous myrosinase. PLOS ONE, 10(11), e0140963. doi:10.1371/journal.pone.0140963