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Unlike cauliflower, which is really three different crops sharing a name, romanesco is a single autumn crop with a single timetable. It is sown in late spring or the very start of summer, planted out by midsummer, builds leaf through the warm months, and heads as the weather cools in mid to late autumn. Total time from sowing to cutting is 100 to 130 days, and on cooler plots more.
That simplicity is a mercy, but it comes with a cost: there is only one attempt per year and no way to catch up. Every stage below has to happen roughly when it says, because the plant has to be at full size by the time the cool weather arrives, and the cool weather does not wait.
The other consequence is that a romanesco takes up a large piece of ground for most of the year. Plan the bed accordingly, and do not put it where you will want to plant something else in late summer.
| Stage | When | Target |
|---|---|---|
| Sow | Late spring to very early summer | Modules under cover or in a sheltered frame |
| Pot on if needed | Two to three weeks after sowing | Never let the plug go solid |
| Plant out | Early to midsummer | Four or five true leaves, netted the same day |
| First top dressing | Three weeks after planting | Nitrogen, hoed in shallowly |
| Second top dressing | Six weeks after planting | Nitrogen with potash; earth up the stem |
| Canopy complete | Late summer to early autumn | A large frame of dark leaves, no head yet |
| Head appears | Mid to late autumn, as nights cool | Stop feeding; keep water even |
| Cut | Two to three weeks after the head shows | Cones sharp, spiral tight |
If you are two weeks behind at the sowing stage you are two weeks behind at every stage after it, and there is nowhere to make it up. Sowing on time is the one deadline in this crop that genuinely cannot slip.
Spring: preparing the bed and sowing
The bed wants preparing well before the plants are ready. Romanesco is a hungry brassica that needs firm ground, and those two requirements pull in different directions: compost has to go in early enough that the soil settles again before planting. Work it in two or three weeks ahead and then leave the bed alone.
Check the pH while you are at it. Brassicas want 6.5 to 7.0, and on acid soil both clubroot damage and trace element shortages get considerably worse. Lime and compost do not go on together, so if the bed needs both, separate them by a fortnight.
- Test and lime the bed if it is acid Aim for pH 6.5 to 7.0. Lime in late winter or very early spring, well before you add compost, and give it time to work.
- Work in compost two or three weeks before planting About 4 lb (2 kg) per square yard of well-rotted compost or manure. Then stop digging, so the soil settles and firms.
- Sow into modules in late spring Two seeds per cell at half an inch (10 mm), germinated at 68 to 77F (20 to 25C), into full light the day they emerge.
- Thin and pot up as needed Cut the weaker seedling out at one true leaf. Tip a plug out weekly, and pot up into three inch (8 cm) pots if the roots are filling the cell before the bed is ready.
- Harden off over seven to ten days Build up outdoor exposure gradually. Wind, not cold, is what damages a soft indoor-raised brassica at this point.
Summer: leaf building
This is the long, quiet part of the crop, and the part people neglect. Nothing visible is happening except that the plant gets larger, but everything about the eventual head is being decided. The whole aim is a canopy that never stops expanding: even water, nitrogen on schedule, no root disturbance, and the net kept on against caterpillars.
By late summer a well-grown plant should be two to three feet (60 to 90 cm) across, with twenty or more large dark leaves and no sign of a head. That is exactly right. A plant that is heading in midsummer has been checked; a plant that is still small in late summer has been starved or crowded.
| Weeks after planting | Job | What to watch for |
|---|---|---|
| Week 1 | Water in, protect from slugs, keep the net sealed | Wilting transplants; shade them for two afternoons |
| Weeks 2 to 3 | Shallow hoe, then first top dressing | Do not hoe deep; the roots are shallow and wide |
| Week 3 | Mulch two inches (5 cm), earth up the stems | Keep the mulch an inch clear of the stem |
| Weeks 4 to 6 | Water a gallon (4 to 5 liters) twice a week | Wilting in the early morning means genuinely dry |
| Week 6 | Second top dressing with potash, earth up again | Floppy leaves mean potash, not more nitrogen |
| Weeks 7 to 12 | Weekly check of leaf undersides and the crown | Egg clusters, and aphid colonies in the growing point |
| Week 10 onward | Stake exposed plants before the autumn winds | A plant rocking at the base has stopped growing |
The single most common summer mistake is easing off on water in the last few weeks before the head appears. Demand is at its highest in exactly that period, and a dry fortnight then costs head size directly.
Autumn: heading and cutting
Once the nights settle into the fifties Fahrenheit (10 to 15C) for a couple of weeks, a full-sized plant switches over and the head appears in the center. From that point everything you do is protective: stop feeding, keep the water even, leave the head exposed to the light, and check it every two days.
The interval from first sight to cutting is two or three weeks in mild autumn weather, shorter if it stays warm, longer and more forgiving if it turns genuinely cold. The head is at its peak for only a few days, so the checking is the whole job.
- Stop all feeding the moment the head is visible Late nitrogen opens the head, softens the spiral and pushes small leaves up between the cones. Nothing you feed now improves the head.
- Keep the water steady Drought followed by a soaking during head expansion is what splits the stem and coarsens the surface. Autumn rain is not always enough under a canopy this wide.
- Leave the head uncovered Romanesco is not blanched. The green color and the crisp geometry both depend on the head developing in full light.
- Check every two days Part the wrapper leaves, look at the cone tips and press the head gently. Sharp cones and firm resistance mean cut now.
- Cut in the morning, wrapper leaves on Take the stem two or three inches (5 to 8 cm) below the head. Carry heads stem-down in a single layer so the cones do not crush.
- Decide whether to leave the plant for side shoots In a mild autumn a plant left with plenty of leaf may produce small spiralled side shoots for a few weeks. If nothing appears in three weeks, or hard frost arrives, pull it.
A light frost improves the flavor and does no harm to a firm head. A hard freeze damages the surface of an exposed head, so cut anything close to ready when a real cold snap is forecast.
How the timing shifts with your climate
The stages above are fixed relative to one another, but where they fall in the year depends on when your weather cools and how long your growing season is. The two constraints never change: the plant must reach full size before the cool weather arrives, and the head must expand in cool rather than hot conditions.
You can settle your own window in a single season by sowing two batches a fortnight apart and recording which one headed better. That one comparison is worth more than any general guidance, because it is measured on your soil and your autumn.
| Climate | Sow | Plant out | Cut | Main risk |
|---|---|---|---|---|
| Mild winters, long autumn | Early summer | Midsummer | Late autumn into early winter | Aphids and pigeons on a long-standing crop |
| Average season | Late spring | Early to midsummer | Mid to late autumn | Sowing late and running out of season |
| Short season, early hard frost | Mid to late spring | Early summer | Early to mid autumn | Cold arriving before the head expands |
| Hot summers | Late spring, and shade the seedlings | Early summer | Late autumn | Heat coarsening the head if it forms too early |
Where autumn is short and frost comes early, romanesco is a genuinely marginal crop and the sowing date has to be at the early end. Where autumn is long and mild, it is one of the easiest and most rewarding brassicas there is.
Recovering a late start
A romanesco sown late does not crop late. It reaches the cool weather at the wrong size, or does not reach heading at all before growth shuts down, and you end up with a large leafy plant and nothing to cut. So the honest answer to lateness is usually to change crop rather than to press on.
- Two weeks late at sowing Carry on, but be strict about everything else. Plant out on time, feed on schedule and never let it go dry. There is no slack left in the season.
- A month or more late at sowing Do not sow romanesco. Put a fast calabrese or an autumn cauliflower in that bed instead, both of which will still make something.
- Plants ready but the bed is not Pot up into three inch (8 cm) pots and feed weakly. Two weeks in a bigger pot costs nothing; two weeks root-bound costs the head.
- Missed the first top dressing Apply it now and keep the second one on schedule. Late nitrogen is only a problem once the head is visible.
- Large plants, no head, and frost forecast There is nothing to be done this year. Pull them, so they do not shelter aphids and disease over winter, and move the sowing date forward by a fortnight next season.
Write down each year's sowing date next to whether the plants headed, and how large the heads were. Two seasons of that record narrows your own sowing window to about a week, and that is the point at which romanesco stops being a gamble.