Cauliflower Heads: Blanching, Ricey Curds and Buttoning

What actually triggers a curd

A cauliflower curd is an arrested flower head: thousands of flower buds that stopped just before they developed. The plant switches from making leaves to making that structure when it has passed a certain size and then experienced a run of cool weather. Both parts matter, and the order matters most of all.

Get the sequence right and you get a big plant that then makes a big head. Get it wrong and the cool spell arrives while the plant is still small, so it makes the only head it can, a button. Everything in this guide comes back to that timing.

The temperature that triggers heading varies by type. Summer types head in warm conditions; autumn and winter types need genuine cold and will sit there making leaves until they get it. Sowing a winter type for a summer crop is a common and completely invisible mistake until nothing heads.

If a plant has made a great deal of leaf and shows no sign of a curd, check the type before you change anything. An overwintering type in late summer is behaving perfectly normally.

Buttoning: a tiny head on a small plant

Buttoning is a curd of an inch or two (3 to 5 cm) appearing on a plant with only a handful of leaves, and then stopping. It is not a disease and there is no treatment. It means the plant was pushed into heading before it had built a canopy, and once the growing point has become a curd the plant cannot go back to making leaves.

Almost every case traces to a check at the seedling or establishment stage: a root-bound module, a dry spell, a cold snap on a young plant, or a transplant that sulked for a week. The cold snap is the most direct trigger, because a young plant that spends weeks below 50F (10C) reads that as its heading signal.

1. Plant out before the roots circle Four to five true leaves, with white roots still visible against fresh compost. A plug that has gone solid has already taken the check.
2. Do not sow too early for your conditions An early sowing that then sits cold for a month outdoors is the classic buttoning recipe. Either give it protection through the cold, or sow later and lose nothing.
3. Keep the water even through establishment The three weeks after planting out are when a dry spell does the most damage. Water in thoroughly and keep the root zone damp until the plant is visibly away.
4. Feed early rather than late A plant short of nitrogen while it is building leaf reaches its heading trigger with too little canopy. The first top dressing at three weeks is the one that prevents buttoning.
5. Cut a buttoned head and use it It will not grow any larger. Cut it small, eat it, and clear the space for something else rather than leaving the plant to occupy the bed.

If several plants button and others do not, look at where they sat. A dry corner, a shaded end or a spot where you hoed deep will usually explain the pattern.

Blanching: covering the curd to keep it white

Left in the open, a cauliflower curd turns cream, then yellow, then a purplish bronze in strong sun. It stays perfectly edible, but the texture coarsens and it looks nothing like a shop head. Blanching means covering the curd with its own leaves so it develops in the dark and stays white.

Start when the curd is the size of an egg, roughly two inches (5 cm) across. Earlier than that you are covering something that has not begun to expand; much later and the color has already set.

1. Check under the leaves twice a week Curds appear suddenly and hide well. From the point where the plant looks full grown, part the inner leaves and look into the center every three or four days.
2. Fold the inner leaves over the curd Gather three or four of the large inner leaves, bend them across the head so they overlap, and tuck the tips under one another. Snapping the midrib slightly makes them stay put.
3. Tie loosely if they will not hold A single loop of soft twine or a rubber band around the folded leaves is enough. Do not bind tightly, and never seal the head in: it needs air moving through it.
4. Re-cover after wind or rain Folded leaves blow open. Look after every windy spell, and reset any head that has been exposed before the sun colors it.
5. Skip it in winter and in the cold Autumn and winter sun is weak enough that many heads stay pale unblanched, and a tied head in wet cold weather traps water and rots. Judge by the light, not by habit.

Some types are described as self-blanching or self-wrapping, with inner leaves that curl over the curd naturally. They still need a look now and then, since the wrap opens as the head expands.

Ricey and fuzzy curds

A ricey curd has lost its smooth surface and looks granular, as though scattered with grains of rice. Fuzziness is the next stage: the individual buds have begun to elongate and separate, and the head is on its way to flowering. Neither can be reversed, so the response is to cut immediately and eat.

The cause is almost always heat, and specifically warm nights during the fortnight in which the curd is expanding. Above about 75F (24C) the buds resume growing instead of staying arrested. Excess nitrogen at the same stage, and a plant that has been left standing past its point, both make it worse.

1. Cut at the first sign of texture The moment the surface stops being smooth, cut. A ricey head is fine to eat, but from that point it deteriorates by the day.
2. Time the crop away from the heat Aim to have the curd expanding in cool weather. For a summer crop that usually means sowing earlier, not later, so heading falls before the hottest weeks.
3. Stop nitrogen once the curd shows Late feeding pushes the buds to keep developing. The last top dressing belongs six weeks after planting, well before heading.
4. Shade a crop caught by a heatwave Shade netting over the row drops the canopy temperature several degrees and can carry heads through a hot spell that would otherwise cost you all of them. Check every second day while it lasts, since the window between a perfect head and a ricey one can be as short as three days.

Loose, leafy and open curds

A loose curd is one that never knits into a solid dome: the sections stand apart, sometimes with small green leaves pushing up between them. It has the same causes as riceyness in a milder form, plus one of its own, which is a plant that started heading and then met conditions that told it to grow again.

That stop-start pattern is the signature. A cold snap during heading, a heavy feed just as the curd appeared, or an erratic water supply will all produce it. Leaves growing through a curd, sometimes called bracting, is the same problem in its clearest form.

Every one of these heads is edible. Trim off browned or flecked areas and use the rest. The reason to identify them is to fix next season's sowing date or feeding, not to decide whether to eat them.

From first sight of the curd to cutting

Once a curd is visible, the timetable is short and mostly out of your hands. In warm weather a head can go from egg-sized to fully expanded in ten days; in cool autumn conditions it may take three or four weeks. The only real decision left is when to cut, and cutting early costs you far less than cutting late.

That is worth recording. Note the date you first saw the curd and the date you cut, alongside the sowing date and the type. After two seasons you will know your own interval well enough to plan the sowings so heads do not all arrive in the same week.

Cauliflowers do not hold on the plant the way cabbages do. If you are away for a week during heading, cut everything that is close rather than hoping to find them in the same condition on your return.