Brussels sprout

Light and exposure

The Brussels sprout wants a sunny, open spot. Give it at least five to six hours of sun a day, in an open corner of the garden where the air moves well. Light supports steady growth and tight sprouts; in shade, it runs up tall and forms loose buds.

An airy spot counts double for this cabbage, because its long foliage holds moisture and attracts disease in a mild, damp summer. Avoid enclosed, permanently damp bottoms of the garden. Watch out for wind too: its tall stem catches a lot, a point we will come back to under pruning.

Watering

The Brussels sprout has a long growing season and needs a cool soil from sowing to autumn. Water regularly and copiously through the summer, at the base, especially during the leaf-development phase and the start of sprout formation. A lack of water at this point gives small, widely spaced buds.

In autumn and winter, the plant slows down and the rain of the cold season is more than enough, often too much. Space out the watering then and let the sky do the work. A summer mulch at the base keeps the soil cool during the hottest weeks of summer, the most critical period for this cabbage that hates going thirsty.

Soil and repotting

This cabbage is hungry and holds the ground for a long time, so it needs a rich, well-supplied soil. Prepare the spot with a good dose of mature compost or well-rotted manure, ideally applied the previous autumn or early in spring. Poor soil gives puny plants that never sprout properly.

It thrives in heavy, deep, cool soils, which suits a clay ground well. A firm soil is even an asset: it anchors the tall stem better. Aim for a neutral to slightly limy pH, around 6.5 to 7, which also helps to hold clubroot in check. On acidic soil, an application of lime a few months before planting is welcome.

Temperature and humidity

The Brussels sprout is a genuine cool-climate vegetable, perfectly at ease in a cool temperate climate. It grows quietly through the mild summer, then gives its best in the cold. It is one of the few vegetables that not only withstands frost but is improved by it.

The first autumn frosts turn part of the sprouts’ starch into sugar: they lose their bitterness and become sweet and fine. An established plant takes frosts of several degrees below zero without flinching and can stay in the ground all winter in an oceanic climate. Only prolonged hard cold below minus 10 degrees can damage exposed sprouts. It is summer heat, more than the cold, that bothers it: growth during a spell that is too hot and dry gives loose sprouts that open.

Pruning and upkeep

The key gesture is not classic pruning but staking and earthing up. The Brussels sprout’s stem rises high, often 60 to 80 centimetres loaded with sprouts, and catches a lot of the autumn wind. Earth up the soil at the base at the end of summer to anchor the base, and put a solid stake for exposed plants, otherwise a gust lays them flat.

Two optional gestures help the harvest. You can remove the large lower leaves as you pick the sprouts, which airs the base. And towards the end of summer, some gardeners top the plant, that is they cut the terminal bud at the top, to concentrate the energy on the sprouts and make them swell faster and more evenly, useful if the autumn looks like being short.

Pests and diseases

Like all cabbages, this one feeds its little army of pests. The cabbage white lays on the foliage and its green caterpillars devour it; inspect the underside of the leaves and remove the eggs, or fit an insect net right from planting. The cabbage root fly attacks the roots of young plants, a cardboard collar at the neck discourages it. Mealy cabbage aphids settle in the heart of the sprouts late in the season, a real nuisance, watch for them and hose the colonies off with a jet.

Clubroot remains the major threat on damp soils: this fungus deforms the roots and makes the plant waste away, and it persists in the soil for years. The only real defence is strict rotation: never replant a cabbage, turnip or radish in the same spot before three or four years. Given the very long cycle of this cabbage that occupies the plot for almost a year, plan its place with care. A drained soil that is not too acidic also slows the fungus.

Propagation

The Brussels sprout is propagated by seed, the only sensible way in the garden. Sow early, at the very start of spring, because its cycle is long and it needs the whole growing season to develop. Sow in a nursery bed under cover or in pots, warm between 15 and 18 degrees, then prick out the seedlings into individual pots as soon as they have a few true leaves.

The final planting takes place in early summer, when the plants are robust. Space them widely, 60 to 70 centimetres in all directions, because they grow big and need air. Plant deep, up to the first leaves, and firm the soil well around the neck for a firm anchorage. Saving your own seed is tricky, because cabbages cross between varieties and are biennial; for a family garden, it is better to start from bought seeds or plants each year.

Month-by-month care calendar

Green Hub tips

• Do not harvest before the first frosts: they turn the starch into sugar and make the sprouts sweet instead of bitter.
• Earth up and stake before autumn. A tall stem loaded with sprouts topples at the first gust of wind if the base is not anchored.
• Pick from bottom to top, sprout by sprout, leaving the plant in the ground: it keeps ripening all winter and supplies you on demand.
• Given the cycle that occupies the plot for almost a year, plan its place in the cabbage rotation from the start to avoid clubroot.
• Brussels sprout seed stays viable for six years and more if it is kept dry, cool and dark, in an airtight bag in the fridge: there is no need to buy fresh seed every year.