Gadenin日本語Get the appSow early, because this one is slow
Romanesco takes far longer than either cauliflower or a summer broccoli. Count on 100 to 130 days from sowing to a cut head, and on some plots closer to 150. It is a plant that wants the whole season: a long stretch of warm weather to build a large frame of leaf, and then a cool run at the end to form the head. Miss either half and you get leaves and nothing else.
That is why the sowing date matters more here than in any other brassica. A cauliflower sown two weeks late still gives you a small head. A romanesco sown two weeks late very often gives you a magnificent three foot plant that never heads at all, because the cool weather it needs arrives while it is still building leaves, and then the real cold shuts everything down before the head can expand.
So the rule is simple and worth being strict about: sow in late spring to early summer, aiming to plant out by midsummer, so that the head expands in the cool weather of mid to late autumn. In practice most people sow romanesco a fortnight earlier than they would sow an autumn cauliflower, and they are right to.
| Sowing time | What the plant does | What you get |
|---|---|---|
| Late spring | Full summer of leaf, heads in cool autumn | Large, fully spiralled heads |
| Early summer | Slightly smaller frame, heads late autumn | Good heads, but a narrower window |
| Midsummer | Still building leaf when the cold arrives | Small heads or none |
| Late summer | Makes leaf, stalls over winter | No head; the plant bolts in spring |
| Early spring under cover | Heads in summer heat | Coarse, loose heads that lose the spiral |
If you are already past the sowing window this year, do not push on and hope. Sow a fast calabrese in that space instead and put romanesco at the top of next season's list, sown a fortnight before you think you need to.
Sowing into modules
Sow into individual cells rather than a communal tray. Romanesco has the same shallow, fibrous root system as the rest of the brassicas, and tearing a seedling out of a shared tray costs it a week of growth that a slow crop cannot spare. A cell of at least one and a half inches (4 cm) across is the minimum.
- Fill and firm the cells before sowing Use a fine seed-starting mix, tap the tray down and strike it level. Loose compost sinks after the first watering and leaves the seed in a hollow that stays saturated.
- Sow two seeds per cell at half an inch (10 mm) Cover lightly and firm the surface with a fingertip. Two seeds insures against a blank cell, and you remove the weaker one later.
- Germinate at 68 to 77F (20 to 25C) In that range seedlings break the surface in four to six days. Below 59F (15C) germination drags on for a fortnight and losses climb. Above 86F (30C) it falls away sharply.
- Water from below Stand the tray in an inch (2 to 3 cm) of water until the surface darkens, then lift it clear. Watering from above shifts the seed and caps the compost.
- Move into full light the day they emerge The moment the stem loops appear, get the tray into the brightest place available. One warm dim day gives you drawn, floppy stems that never recover their stiffness.
- Cut the weaker seedling out at one true leaf Snip it off at compost level with scissors rather than pulling. Pulling disturbs the roots of the seedling you are keeping, which is exactly the check you are trying to avoid.
Growing them on without a check
Everything about romanesco depends on a plant that has never stopped growing. Its head is built out of the leaf area that exists at the moment heading starts, and unlike a cabbage it gets one attempt at it. A seedling that sat dry for two days, or spent a fortnight root-bound in a full cell, will still look green and still go on to make a head, but it will make a small, flat one with a poor spiral.
The signal to watch is the root, not the leaf. By the time a romanesco seedling looks pale, the check happened a week ago. Tip one plug out of its cell weekly and look at the sides: white roots visible with compost still showing between them is right, and a solid mat with no compost visible means you are already late.
Keep them cooler than germination temperature but never genuinely cold. Long runs below 50F (10C) on a young brassica are read by the plant as its heading signal, and on a romanesco that has barely six leaves the result is a button the size of a walnut.
| Stage | Day temperature | Night temperature | Root check |
|---|---|---|---|
| Germination | 68 to 77F (20 to 25C) | Same | None needed |
| Seed leaves to first true leaf | 61 to 68F (16 to 20C) | 54 to 59F (12 to 15C) | None needed |
| Two to four true leaves | 59 to 68F (15 to 20C) | 50 to 57F (10 to 14C) | Tip one plug out weekly |
| Potted up | Ambient, in full sun | Above 50F (10C) | Check again after ten days |
| Hardening off | Outdoor temperature | Above 45F (7C) | Should be well rooted but not solid |
If the bed is not ready when the plants are, pot up into three inch (8 cm) pots with a compost that has some nutrition in it. Two weeks in a bigger pot costs nothing. Two weeks root-bound in a module costs the head.
Planting out into firm ground
Plant out at four to five true leaves, on a plant six to eight inches (15 to 20 cm) tall with a stem stiff enough to hold its own leaves up. Older than that and the roots are already restricted; younger and it has no reserves against wind, slugs or a hot afternoon.
Romanesco makes a very large plant, commonly two to three feet (60 to 90 cm) across, and it carries a heavy head on a single stem late in the season when the weather turns windy. Firm ground is not a nicety here. Plant into soil that has settled for a fortnight after digging, press it down hard around the plug, and give the plants far more room than feels reasonable when you are handling a six inch seedling.
- Harden off over seven to ten days Start with two or three hours in a sheltered, part-shaded spot and build up to a full day out. Wind toughens the leaf more than cold does, and does more damage if you skip the process.
- Water the tray an hour before lifting A dry plug crumbles as it comes out and half the root hairs tear away. Wet, it slides out whole and goes into the hole intact.
- Space at 27 to 30 inches (70 to 75 cm) each way This is wider than for cauliflower and it is not negotiable. A crowded romanesco makes a small head, and a wet canopy all autumn on top of it.
- Plant deep, up to the seed leaves Setting the stem an inch (2 to 3 cm) lower than it sat in the pot anchors a plant that will become top-heavy. Keep the growing point clear of soil.
- Firm until the plant resists a tug Press the soil down around the plug with your knuckles, then take hold of a leaf and pull gently. If the leaf tears before the plant moves, it is firm enough. A loose brassica rocks in wind and never roots properly.
- Water in with a gallon (4 to 5 liters) per plant Pour it slowly into the planting hole so it soaks down to the base of the plug rather than spreading across the surface.
- Net the row the same day Cabbage white butterflies find a newly planted brassica within hours. Netting put up on planting day prevents most of the season's pest work in a single job.
Shade each plant with an upturned pot or a piece of netting for the first two afternoons if it is hot and bright. Wilting on day one is a check like any other, and on a crop this slow you have no time to make it up.
What to write down now
Romanesco failures show up four or five months after their cause, which puts them well beyond anything you will reconstruct from memory. A handful of lines noted at sowing and planting turns next season from guesswork into an adjustment.
| Record | Why it matters later |
|---|---|
| Sowing date | Days to heading run 100 to 130. Without the date you cannot tell whether a headless plant was late or starved |
| Date planted out and leaf count | If heads came small and flat, this shows whether you planted an over-restricted plug |
| Any wilt, cold snap or missed watering | Each of these is a check, and one note explains a poor spiral months later |
| Spacing actually used | Head size tracks spacing closely on a plant this large |
| Position of each plant in the bed | Lets you match a failure to the dry end, the shaded corner or the wet strip |
Record the checks even when the plants recovered and looked fine afterwards. The recovered seedling is precisely the case you will not remember, and precisely the one that explains the disappointing head.