Why is my cauliflower forming a tiny head?

Buttoning is a check to growth in a plant that then flowers anyway — the transplant, water and nitrogen faults that cause it, plus ricey and blind curds.

Difficulty: intermediate
Time: 15 min
Read: 4 min

Short answer

A cauliflower that has been checked — pot-bound, transplanted badly, gone short of water or nitrogen — switches to producing its curd while it is still small, and you get a button. Keep the plant growing without a single interruption from sowing to harvest; there is no way to fix it once the curd has started.

Cauliflower is the least forgiving vegetable in the brassica bed, and buttoning is why. The plant makes one decision, once, about when to stop growing leaves and start making a curd, and a check in growth brings that decision forward. Everything about growing good cauliflower is about preventing checks.

Step by step

Raise plants without letting them get pot-bound.A cauliflower seedling that sits too long in a small module is already checked before it goes out. Pot on promptly, or sow in a seedbed and transplant while young.
Transplant carefully and water in well.Move plants when they are small, keep the root ball intact, plant firmly, and water thoroughly. A wilted transplant is a checked transplant.
Never let them go short of water.Cauliflower is thirsty and shallow-rooted. A dry fortnight in summer causes buttoning weeks later. Water heavily in dry spells and mulch.
Feed steadily with nitrogen through the growing phase.Cauliflower needs more nitrogen than most brassicas and needs it continuously. A plant that runs out mid-season buttons. Feed at planting and again as growth accelerates.
Plant into firm, well-prepared, limed soil.Rich, moisture-retentive soil with plenty of organic matter, firmed, near-neutral pH. Cauliflower rewards preparation more than any other brassica.
Space generously.About 60cm each way for summer and autumn types. A crowded cauliflower is a checked cauliflower.
Match the variety to the season.Summer, autumn, winter and spring-heading cauliflowers are different types with different sowing windows. A type sown out of window buttons or fails to head at all.
Protect the curd once it forms.Bend a couple of outer leaves over the curd, or snap them across the plant, to keep sun and frost off. It keeps the curd white and firm.
Cut promptly once the curd is full.A cauliflower goes from perfect to ricey — the surface breaking into separate grains — within days in warm weather. Cut in the morning while it is cool and firm.

Tips

Cauliflower is genuinely harder than calabrese. If you want a reliable crop from the same bed and the same effort, grow calabrese or purple sprouting broccoli instead.
Buttoned curds are edible and taste fine — they are just small. Cut them and use them rather than leaving the plant standing.
Overwintered winter cauliflowers are a different proposition: they are hardy, stand through winter and head in spring, and they need far less summer water than a summer variety.
Romanesco and coloured varieties behave like cauliflower and have the same intolerance of checks.

Common mistakes

Buying leggy pot-bound plants from a garden centre — They are already checked. A cauliflower that has sat in a small pot too long will button whatever you do afterwards.
Treating cauliflower like cabbage — Cabbage tolerates a dry spell and recovers. Cauliflower responds by making a curd, and that decision cannot be undone.
Skipping the mid-season feed — Cauliflower is the hungriest brassica. Running out of nitrogen halfway through is a common cause of small heads.

If it doesn't work

Tiny curd on a small plant early in the season

Cause: Buttoning after a check — pot-bound, transplant shock, drought or nitrogen shortage — Fix: Cannot be reversed. Cut and use it. Next time avoid every check between sowing and harvest.

Curd breaking into separate grains

Cause: Ricey curd, from heat or from being left too long — Fix: Cut at once and use it — it is edible but coarse. Cut earlier in future and grow in cooler weather.

Large healthy plant, no curd at all

Cause: Blindness, or a variety out of season — Fix: A blind plant will not produce. Use the leaves as greens. Check the variety's season next time.

Curd turning yellow or purple

Cause: Sun exposure — Fix: Break outer leaves over the curd as it develops. Discolouration is cosmetic and it is still good to eat.

Brown patches through the curd

Cause: Boron deficiency, or frost damage on winter types — Fix: Cut out affected parts. Boron deficiency is more likely on very alkaline or heavily limed soils; do not over-lime brassica beds.

Questions people ask

Can a buttoned cauliflower grow into a full-sized one?

No. Once the plant has switched to producing a curd it will not go back to making leaves, so the head stays small. Cut it and eat it.

Is a ricey cauliflower safe to eat?

Yes, it is just past its best — the curd has started to separate as it moves towards flowering. It is coarser in texture but perfectly good cooked, particularly broken into a gratin or a soup.

Why do mine never head at all?

Usually the wrong type for the sowing date, so the plant never receives the seasonal cue it needs, or a serious check when young. Check the packet's stated sowing window against what you actually did.