Gadenin日本語Get the appWhat triggers the head
The head of a romanesco is an arrested flower head, the same structure as a cauliflower curd, but arranged in a repeating spiral of pointed cones. The plant switches from making leaves to making that structure once it has passed a certain size and then met a run of cool weather. Both conditions are required, and the order is what decides whether you get a crop.
Get the sequence right and a large plant meets the cool weather with a full canopy and turns it into a big, deeply sculpted head. Get it wrong in one direction and the cool weather arrives while the plant is small, so it makes the only head it can, a button an inch or two across on a plant with eight leaves. Get it wrong in the other direction and the plant is still building leaf when the real cold shuts growth down, and it heads the following spring, if at all, as a bolted mess.
The temperature that matters is around 50 to 59F (10 to 15C) sustained for a couple of weeks. That is why romanesco is an autumn crop nearly everywhere: it wants the cool that arrives as the nights draw in, on a plant that had the whole summer to grow.
| Situation | What the plant does | Result |
|---|---|---|
| Large plant, cool weather arrives | Switches to heading with a full canopy | A large, fully spiralled head |
| Small plant, cool weather arrives | Heads anyway, on eight or ten leaves | A button that never expands |
| Large plant, weather stays warm | Keeps making leaf and waits | Heads later, once it finally cools |
| Large plant, cold arrives before heading | Growth stops entirely | No head; bolts in spring |
| Head forming in warm weather | Buds resume growing | Coarse, loose head with a poor spiral |
A romanesco making a great deal of leaf in late summer and showing no sign of a head is behaving normally. Do not feed it more nitrogen in an attempt to hurry it. Check the sowing date instead and wait for the cool weather.
The commonest failure: sown too late
More romanesco crops are lost to a late sowing than to everything else put together. At 100 to 130 days from sowing to cutting, the crop needs practically the whole season, and there is no slack in it. A sowing that goes in a fortnight late does not simply crop a fortnight later. It runs into the shortening days and falling temperatures of late autumn with the plant still on its leaf-building phase, and a brassica that has not started heading by then will not start until spring.
What you see is a very large, healthy, entirely useless plant. Three feet across, dark green, obviously well fed, and with nothing in the middle. It sits like that through the winter and then, when the days lengthen, it goes straight to flower without ever making the head.
The remedy is entirely at the sowing end. Work backwards: decide the fortnight when your weather reliably turns cool, subtract 100 to 130 days, and sow then. If that date has passed, do not sow romanesco this year.
- Count back from your cool weather, not forward from spring Head expansion needs the two or three weeks when nights are consistently in the fifties Fahrenheit (10 to 15C). Everything before that is leaf building, and it takes three or four months.
- Sow a fortnight earlier than for autumn cauliflower Romanesco is slower than cauliflower by two to four weeks. Sowing them on the same day is the mistake that produces headless plants.
- Plant out by midsummer at the latest The plant needs the long warm days to build its frame. A transplant that goes in during late summer has run out of the growing weather it needs.
- Do not try to force a late plant Extra nitrogen on a late plant makes it larger, not earlier. Heading is triggered by size and temperature, and you cannot supply the second one.
- Pull headless plants at the end of the season A plant that has not begun to head by hard frost will not produce anything worth eating. Clear it, so it does not harbor aphids and disease through the winter, and free the bed.
On mild plots a headless romanesco occasionally does head in early spring before it bolts. Leave one or two if you have the space and want to find out, but never plan on it.
No blanching needed
Cauliflower growers reach for the blanching habit automatically, and it is wrong here. A romanesco head is meant to be green. The color comes from chlorophyll developing in the light, and the whole visual appeal of the crop, the sharp lime-green cones in their spiral, depends on the head being exposed to the sun as it expands.
Fold the leaves over a romanesco and you get a pale, yellowish head with a soft, washed-out spiral and, if the weather is wet, a rotten patch where the water was trapped. Leave it open. The only reason to touch the leaves at all is to look underneath, and you should do that often.
The one exception is a genuine heatwave during head expansion. Shade netting over the row for a few days drops the canopy temperature enough to save heads that would otherwise go coarse. That is shading against heat, not blanching against light, and it comes off as soon as the weather breaks.
| Practice | Cauliflower | Romanesco |
|---|---|---|
| Folding leaves over the head | Yes, from egg size, to keep it white | No; the head should be green and exposed |
| Tying the wrapper leaves | Sometimes, loosely | Never; it traps water and softens the spiral |
| Shade netting in a heatwave | Useful during head expansion | Useful, and removed as soon as it cools |
| Checking under the leaves | Twice a week once full grown | Twice a week, and more once the head shows |
| Color when ready | White or cream | Bright lime green, sometimes yellowing in strong sun |
A romanesco head that has gone yellowish-green in strong late sun is still perfectly good to eat. It is a cosmetic change, not a sign of over-maturity, and it is quite different from the loosening that means you have left it too long.
Buttoning and coarse heads
Buttoning is a head an inch or two (3 to 5 cm) across appearing on a plant with only a handful of leaves, and then stopping. There is no treatment and no way back, because the single growing point has already become a head. It means the plant met its heading trigger before it had built a canopy, and the usual cause is a check at the seedling or establishment stage: a root-bound plug, a dry fortnight, or a spell of cold weather on a small plant.
Coarseness is the opposite fault. A head that expands in warm weather has buds that resume growing instead of staying arrested, so the cones lengthen and separate, the surface loses its crispness, and the geometry blurs into something that looks like an untidy broccoli. Excess nitrogen at the same stage makes it worse, and so does uneven water.
| Fault | What it looks like | Cause | Prevention |
|---|---|---|---|
| Buttoning | A tiny head on a small plant | A check at the seedling stage, or cold on a young plant | Plant unrestricted plugs; feed early; do not sow too early |
| No head at all | A huge leafy plant with nothing in the center | Sown too late for the season | Sow in late spring; count back from the cool weather |
| Coarse, blurred spiral | Cones elongated, surface no longer crisp | Warm weather during head expansion | Time heading into cool weather; cut promptly |
| Loose, open head | Sections standing apart | Stop-start growth as the head forms | Even water; no nitrogen once the head shows |
| Leaves through the head | Small green leaves between the cones | A check and restart during heading | Steady conditions from first sight to cutting |
| Brown flecking inside | Brown spots through the head | Boron shortage on acid soil | Correct pH; borax only where confirmed, and never twice |
Every one of these heads is edible. Trim the browned parts and use the rest. The point of identifying which fault you have is to change next year's sowing date or feeding, not to decide whether to eat it.
From first sight to cutting
Once the head is visible in the center of the plant, the timetable is short and mostly out of your control. In mild autumn weather a romanesco goes from the size of an egg to full size in two to three weeks. In warm weather it can be ten days, and the head coarsens at the end of it. In genuinely cold weather it may take a month and hold beautifully while it does.
This is the interval most worth recording. Note the date the head first became visible and the date you cut, alongside the sowing date. After two seasons you will know your own interval well enough to stagger sowings so the heads do not all arrive in the same fortnight, which on a crop that occupies the ground this long is a real gain.
| Stage | Head size | What to do |
|---|---|---|
| First visible in the center | Under 1 in (2 cm) | Note the date; stop feeding; keep water even |
| Egg sized | About 2 in (5 cm) | Leave it exposed; check every three days |
| Expanding | 3 to 5 in (8 to 12 cm) | Check every two days; shade only in a heatwave |
| Spiral fully defined, cones sharp | 6 in (15 cm) and up | This is the peak; cut now |
| Cones separating, surface softening | Any size | Cut today; it will not improve |
The window at which a romanesco is at its best is genuinely short, often only three or four days. If you are going to be away during head expansion, cut everything that is close rather than expecting to find it in the same condition when you get back.