Cauliflower Care: Watering, Feeding and Unchecked Growth

Leaf area now is head size later

The curd is built entirely out of what the leaves have made before it forms. A plant that carries twenty large, dark leaves at the moment it starts heading gives a heavy, dense head; a plant with twelve small ones gives a head you could hold in your palm, no matter what you feed it afterwards. Feeding once the curd shows is largely too late.

That single fact drives all cauliflower care. From planting out until the curd is the size of an egg, the whole job is growing leaves fast and without interruption. After that, the job changes to protecting the curd, and the feeding stops mattering.

Cauliflower is also a hungry, thirsty plant with a shallow, fibrous root system. It has neither the deep roots to find water in a dry spell nor the frugality to cope with poor ground. If your plot is light and dry, this is the brassica that will show it first.

Judge progress by leaf count and leaf size rather than by height. A cauliflower that has put on four large new leaves in a fortnight is doing well; one that has grown taller without much new leaf is short of something.

Watering: steady beats generous

Cauliflower needs about an inch (25 mm) of water a week, and considerably more in hot, windy weather when a large leaf canopy is transpiring hard. Wilting in the middle of a hot day is not automatically a problem; wilting in the early morning is, and means it has been short of water overnight.

The pattern matters more than the total. A cycle of drought followed by a soaking is what produces the small, ricey curds and the sudden splitting of the stem. Even watering makes a plant that grows steadily, which is exactly what a cauliflower wants.

1. Water at the base, not over the leaves The canopy sheds water outwards, so overhead watering runs off and leaves the root zone dry. Aim the can at the soil around the stem and give it time to sink in.
2. Give a gallon (4 to 5 liters) per plant, less often A thorough soak twice a week beats a splash every day. Light watering keeps the roots at the surface, which is where the soil dries first.
3. Check by digging, not by looking Push a finger two inches (5 cm) into the soil. Dark on the surface after a shower means almost nothing; the root zone can still be bone dry underneath.
4. Increase sharply as the head starts The fortnight in which the curd expands is when water demand peaks. A dry spell now shrinks the head directly and can make it ricey.
5. Mulch once the soil has warmed Two inches (5 cm) of compost or straw around the plants, kept clear of the stem, halves the swing in soil moisture and saves most of the weeding.

Overwintering plants are the exception. Sitting in cold, saturated soil rots the roots, so on heavy ground grow them on a ridge or a raised bed and water only in genuinely dry winter spells.

Feeding for leaf, then stopping

Cauliflower wants a lot of nitrogen, and it wants it early. Work well rotated compost into the bed before planting, then top dress twice during the leaf-building phase. Once the curd is visible, stop: late nitrogen produces leafy, loose curds and soft growth that pests find first.

Potassium and calcium matter more than gardeners usually assume. Weak, floppy leaves and a plant that never firms up often reflect a soil short of potash rather than nitrogen. Cauliflower also wants a near-neutral soil, pH 6.5 to 7.0, which is where the trace elements it needs stay available.

Scatter top dressings in a ring six inches (15 cm) out from the stem and hoe them in shallowly. Fertilizer against the stem scorches it, and deep hoeing cuts the surface roots you are trying to feed.

Boron and molybdenum: the two that bite

Cauliflower is unusually sensitive to two trace elements, and both produce symptoms that look like something else entirely. Boron shortage gives hollow, brown-streaked stems and a bitter, brown-flecked curd. Molybdenum shortage gives whiptail, where new leaves come through as narrow straps with almost no blade.

Both are far more common on acid soil, because low pH locks the elements up even when they are present. On a plot that has been limed for brassicas you are unlikely to see either. On an untested acid plot they are among the first things to check when the plants look wrong in a way that feeding does not fix.

Boron is toxic in excess and the margin is narrow. Never apply it as an insurance measure, only in response to symptoms, and never twice in a season.

Weeds, hoeing and root disturbance

Cauliflower roots run wide and shallow, sitting in the top three or four inches (8 to 10 cm) of soil right out to the edge of the leaf canopy. That is precisely where a hoe goes. Weeding a cauliflower bed deeply is a self-inflicted check, and one that people repeat every year without connecting it to the small heads.

Deal with it by getting the weeds early and then mulching. Once the canopy closes, the plants shade the ground themselves and weeding stops being necessary.

1. Hoe shallowly and only in the first month Skim the surface at half an inch (1 cm) deep while the plants are still small and the roots have not spread. After that, mulch instead.
2. Hand pull anything close to the stem Within six inches (15 cm) of the plant, pull weeds by hand when the soil is damp so they come out whole rather than cutting the roots.
3. Earth up the stems at the second feed Drawing two inches (5 cm) of soil up the stem stabilizes a top-heavy plant and encourages roots along the buried stem. Loose plants that rock in wind head poorly.
4. Stake exposed or overwintering plants A cane and a soft tie on plants in a windy site or in winter stops the root plate being levered loose, which is a common cause of overwintered plants failing to head.

Reading the plant week by week

A cauliflower tells you what it is short of, but the signals are easy to misread because several problems make the plant look small and pale. Look at which leaves are affected first, and whether the new growth is normal in shape.

Note the date on which you first see the curd, alongside the sowing date. Over two or three seasons that pairing tells you exactly how long your conditions take, which is worth more than any figure on a packet.