Broccoli is a productive UK crop that grows best in fertile soil with steady moisture and plenty of room.
This guide covers the large green-headed broccoli commonly grown in the UK, technically known as calabrese. Growing purple sprouting broccoli instead? Use the dedicated How to Grow Purple Sprouting Broccoli in the UK guide.
Broccoli or Calabrese?
In UK gardening, the large green central head most people call broccoli is usually calabrese.
| Type | What you harvest | Typical cropping habit |
|---|---|---|
| Calabrese | One main green head followed by smaller side shoots | Faster summer and autumn crop |
| Purple sprouting broccoli | Repeated smaller spears | Long-season crop harvested the following winter or spring |
When to Sow and Plant Broccoli in the UK
Broccoli is generally sown from March to June, depending on whether you start plants under cover or outside.
| Job | Typical UK timing |
|---|---|
| Sow under cover | March–April |
| Sow outdoors | April–June |
| Plant outside | May–July |
| Harvest | Usually July–October |
For an early crop, sow in modules under cover from March. From April onwards, broccoli can also be sown outside in modules or a seedbed and transplanted later. Keep seedlings cool, bright and growing steadily rather than pushing them with excessive warmth.
BYF Variety Pick: Calabrese ‘Marathon F1’ AGM
If you want a dependable green-headed broccoli, ‘Marathon F1’ is a strong all-round choice. It is a vigorous, slow-to-bolt variety with good disease resistance and a long harvest period from summer into autumn. Cut the main head first and the plants should continue producing smaller side shoots afterwards.
Where to Grow Broccoli
Choose a position with:
- Full sun or light shade
- Fertile, moisture-retentive soil
- Good drainage
- Firm ground
- Enough space for plants to mature
- Room to protect the crop with netting or mesh
On poorer ground, work in well-rotted compost before planting. Brassicas also prefer firm soil, so tread or firm recently dug ground gently before planting to anchor young plants well.
How to Sow Broccoli
For most gardeners, sowing into modules is the simplest method.
- Fill modules or small pots with peat-free seed compost.
- Sow shallowly, cover lightly and water.
- Keep the compost moist and give seedlings plenty of light.
- Thin to the strongest plant if more than one seed germinates.
Keep young plants growing steadily. Poor light, dry compost or excessive warmth can check their growth.
Before planting out, harden indoor-raised plants off for around a week by gradually increasing the time they spend outdoors.
Planting Broccoli Outside
Broccoli is ready to plant once the young plants are sturdy, well rooted and roughly 10–15cm tall.
- Water the seedlings before planting.
- Plant into firm, weed-free soil.
- Firm each plant well and water it in.
- Fit crop protection straight away where pigeons or cabbage whites are a problem.
How Far Apart to Plant Broccoli
Spacing affects both the size of the plant and the size of the head it produces.
| Spacing | Best suited to |
|---|---|
| Around 30cm apart | Smaller plants and heads, or limited space |
| Around 45cm apart | Larger plants with more room to develop |
| Around 45cm between rows | Access for watering, weeding and harvesting |
Avoid squeezing broccoli plants together simply because they look small when planted. Mature plants take up considerably more room.
Plan the Bed Before You Plant
Broccoli takes more room than the young plants suggest. Use the free BYF Allotment Planner to space your crop properly and see how many plants will actually fit your bed.
Watering, Feeding and Caring for Broccoli
Once broccoli is established, keep it growing steadily.
Watering
Water regularly until plants establish, then water deeply during dry spells. Consistent moisture becomes particularly important as the heads begin to form.
Feeding
Broccoli grown in fertile soil rarely needs regular feeding. On poor ground or where plants look weak, a nitrogen-rich feed can encourage stronger growth.
Mulching
A layer of compost or organic mulch helps retain moisture and suppress weeds.
Common Broccoli Problems
Most broccoli problems are easier to deal with when caught early.
| What you see | Likely cause | What to do |
|---|---|---|
| Small head forms too early | Buttoning/checked growth | Keep young plants growing steadily and avoid planting badly stressed seedlings |
| Plant starts flowering | Bolting or stress | Keep watering consistent and harvest promptly |
| Holes in leaves | Caterpillars | Check leaves and protect with fine mesh |
| Young plants badly damaged | Slugs or snails | Protect plants while they are small |
| Grey-green insects around shoots | Aphids | Check growing tips regularly and remove colonies early |
| Plant wilts and roots are swollen | Clubroot | Remove affected plants and improve brassica rotation |
Protecting Broccoli with Netting
Fine insect mesh helps protect broccoli from cabbage white butterflies and several other brassica pests, while netting can deter pigeons. Support the covering above the crop and secure the edges so pests cannot get underneath.
When and How to Harvest Broccoli
Harvest once the head is firm and tightly budded, before the yellow flowers begin opening.
Harvesting the Main Head
Cut the central head with a sharp knife, taking a short section of stem with it.
A main head around 10–15cm across is often ready, although final size varies with variety and growing conditions.
Leave the Plant After Harvesting
Do not pull the plant out after cutting the main head.
Many varieties produce smaller side shoots from lower down the stem, giving you several additional harvests over the following weeks.
FAQ
Calabrese is usually harvested from July to October, depending on the variety, sowing date and growing conditions. Harvest once the head is firm and tightly budded, before the yellow flowers begin opening.
It does not grow another full-sized central head, but many varieties produce smaller side shoots after the first head is harvested.
Broccoli eventually flowers naturally, but premature flowering can be encouraged by stress such as dry soil, checked growth or hot conditions. Harvest heads while the buds are still tight.
Small premature heads are often known as buttoning. It can happen when young plants are stressed or their growth is checked.
Full sun is ideal, although broccoli can tolerate some light shade. Avoid deeply shaded positions where growth will be weak.
Protection is strongly worthwhile where pigeons or cabbage white butterflies are common. Fine insect mesh is particularly useful because it physically prevents many pests from reaching the crop.
Yes, but broccoli is usually easier in the ground. Use a large container for one plant, fertile compost and keep it well watered.
The green central head commonly called broccoli in the UK is generally calabrese. Purple sprouting broccoli is a longer-season brassica grown for repeated small spears, usually harvested in late winter or spring.
