How to Grow Broccoli Without It Bolting or Buttoning

Broccoli fails in two distinct ways, and they look similar but have opposite causes.

Bolting is heat — the plant flowers instead of heading. Buttoning is a tiny head on a small plant, caused by a check to growth while it was still a seedling. Getting broccoli right is mostly about avoiding both.

Timing is most of it

Broccoli wants to grow in cool weather and finish before heat. That gives two windows:

• Spring: start indoors 6 to 8 weeks before the last frost, plant out 2 to 4 weeks before it. Risky — the head forms as temperatures rise.
• Autumn: the better bet. Count back the variety’s days to maturity from your first expected frost, add a couple of weeks, and sow then. The plant matures into cooling weather, which is exactly what it wants.

Broccoli tolerates frost well, and light frost improves the flavour.

Soil

Brassicas are hungry and want firm, fertile, slightly alkaline ground.

• Dig in compost or well-rotted manure before planting.
• pH 6.0 to 7.5. On acidic soil, lime it — alkaline conditions also suppress clubroot, which is why mushroom compost suits brassicas particularly well.
• Firm the soil. Brassicas dislike loose ground and rock in wind, which damages the roots. Tread the bed before planting and firm around each plant.
• Full sun, though broccoli tolerates light shade better than most vegetables.

Sowing and planting out

Sow in modules rather than a seed tray, half an inch deep, and pot on or plant out before the roots start circling.

This is the buttoning prevention step. A seedling that becomes root-bound, dries out, or runs short of nitrogen concludes that conditions are hostile and rushes to reproduce — producing a tiny head on a plant with no frame to support a real one. Once it has buttoned, nothing recovers it.

Plant out at four to six true leaves, 18 to 24 inches apart, rows 24 to 36 inches apart, setting them slightly deeper than they sat in the module and firming well.

Water and feed

Consistent water — about an inch to an inch and a half a week, more in heat. Broccoli is shallow rooted and checks quickly when dry, and a check is what triggers both buttoning and bolting.

Mulch to hold that moisture steady and keep the roots cool.

Feed nitrogen early. Unlike fruiting crops, broccoli wants nitrogen throughout — you are growing leaves and a flower bud, not fruit, so the switch to potassium described for tomatoes does not apply here. A nitrogen-rich feed three or four weeks after planting out, and again a few weeks later, is about right.

Harvest, and the second crop

Cut when the head is full and firm and the individual buds are still tight. The moment they begin to loosen and show yellow, it is flowering and the quality drops quickly.

Cut the main head with four to six inches of stem, at an angle so water runs off the cut.

Then keep the plant fed and watered. Most varieties produce side shoots from the leaf joints — smaller florets that can crop for several more weeks, and often add up to more than the main head. Varieties bred for a single large head produce fewer, so check the packet if the second crop matters to you.

Broccoli does not store well fresh — a few days in the fridge — but freezes well after blanching.

Pests

Brassicas attract more pests than almost anything else in a vegetable garden, and the answer is nearly always exclusion.

Fine mesh over hoops from the day of planting deals with most of that list at once, which is the same logic as excluding carrot fly. Rotate brassicas on a three- to four-year cycle, because clubroot persists in soil for years.