Why Broccoli Doesn’t Form Heads (and How to Fix It)
Broccoli plants that grow tall and leafy but never produce a head can be puzzling. Sometimes there's a real problem, such as a dry spell, crowding or poor soil. But very often the plant is simply a type that crops later than expected, or a head formed and flowered before anyone noticed. Working out which type you're growing is the first step.
Quick answer
Broccoli usually fails to head for one of three reasons. It's a type that isn't due yet, as winter sprouting broccoli doesn't crop until late winter. Its growth was checked, by drying out, being moved in warm weather or planted in poor soil. Or it flowered early in hot weather. Grow calabrese for summer and autumn heads, keep plants watered, space them properly and pick promptly once buds form.
What's wrong with your broccoli?
Big, healthy plants with no heads in autumn: see "Not ready yet".
Small heads that open into yellow flowers: see "Flowering early".
Plants small and slow: see "Hungry soil", "Dry soil" and "A check in growth".
Only small shoots after the main head: see "Side shoots are normal".
Plants wilting and not growing: see "Root damage".
Centre of the plant eaten or missing: see "Pests in the growing tip".
Not ready yet
This is the most common cause of worry. There are two kinds of broccoli, and they crop at very different times:
Calabrese, with one big green head, is ready three to four months after sowing, usually from July to October.
Sprouting broccoli takes four to ten months. Traditional winter varieties grow big and leafy through summer and autumn, and only produce their spears in late winter and early spring.
Fix it: check which type and variety you sowed. If it's winter sprouting broccoli, leave it be. The spears will come.
For sowing and cropping times by type, see when to plant broccoli in the UK
Flowering early
In hot weather, broccoli can rush into flower before the head reaches a proper size. The buds loosen and open into yellow flowers, sometimes within a day or two. Calabrese is especially prone to this.
Fix it: keep plants well watered in hot spells, and check them every few days once heads start to form. Pick any small heads as soon as you see them, before they open. In warmer areas, choose bolt-resistant varieties.
For signs a head is ready, see when to harvest broccoli
A check in growth
Young calabrese doesn't like being moved, especially in warm weather. Plants that are transplanted late, dry out after planting or aren't hardened off can stall, then produce a small early head instead of a full one.
Fix it: plant out when plants are 10–15 cm tall, before hot weather arrives, and move them with the rootball intact. From May onwards, sow calabrese straight into its final spot so it never has to be moved.
For more detail, see how to harden off seedlings
Dry soil
Broccoli needs steady moisture while it's growing, and calabrese is especially sensitive as the head forms. A dry spell at that stage often means small heads or early flowering.
Fix it: water thoroughly in dry weather, and more often as heads start to form. A mulch of compost helps hold moisture in.
For more detail, see how often to water broccoli
Too crowded
Crowded broccoli competes for light, water and food. Calabrese planted closer than recommended gives smaller heads.
Fix it: space calabrese 30 cm apart (45 cm for larger varieties) in rows 45 cm apart. Sprouting broccoli needs much more room, 60–80 cm each way.
Hungry soil
Broccoli is a hungry crop. In thin, poor soil, plants stay small and struggle to produce good heads or spears.
Fix it: dig in about two buckets of well-rotted manure or garden compost per square metre before planting. On poor soil, give a high-nitrogen feed when plants are about 20 cm tall.
For more detail, see best soil for vegetable gardening in the UK
Acid soil
Broccoli prefers soil that isn't acidic, around pH 6 to 7 for sprouting broccoli and 6.8 or above for calabrese. Acid soil also encourages clubroot.
Fix it: test your soil, and if it's acidic, lime the bed the winter before planting.
Root damage
Plants that wilt on warm days and stop growing may have damaged roots. Cabbage root fly maggots eat the roots of young plants, and clubroot swells them into knobbly lumps.
Fix it: cover young plants with insect-proof mesh from planting out. To limit clubroot, rotate crops, lime acid soil and start plants in modules so they go out with strong roots.
Pests in the growing tip
The head forms at the very top of the plant. If caterpillars or pigeons damage that growing tip, the plant may never form a proper head.
Fix it: keep broccoli under fine mesh, held up on canes or hoops, from planting out.
Side shoots are normal
After you cut a calabrese head, the plant doesn't grow another big one. Instead it produces smaller side heads for several weeks. This is normal, not a sign that something is wrong.
Fix it: keep picking the side shoots before they flower, and the plant will keep producing them.
Broccoli in containers
Broccoli in pots dries out quickly, which makes early flowering and small heads more likely. Calabrese is the better choice for containers, and it needs steady watering.
For more detail, see growing broccoli in containers
For the whole growing season, see how to grow broccoli in the UK. For related crops, see why cauliflower doesn't form heads and why cabbage doesn't form heads
Common questions
Why is my broccoli not producing heads?
If it's sprouting broccoli, it may not be due yet, as winter varieties crop in late winter and spring. Otherwise, dry soil, crowding, poor soil or a setback after planting are the usual causes.
Why is my broccoli flowering before the head forms?
Hot weather or a check in growth makes broccoli rush into flower. Keep plants watered, check them every few days as heads form, and pick small heads before they open.
How long does it take for broccoli to form a head?
Calabrese forms a head about three to four months after sowing. Sprouting broccoli takes four to ten months, depending on the variety.
Does broccoli grow back after cutting the head?
Calabrese produces smaller side shoots after the main head is cut, not a second large head. Sprouting broccoli keeps producing spears for up to two months.
Causes, timings, spacing and care based on RHS guidance.