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Brussels Sprouts

This Allotment Pro editorial draft summarises the cited RHS guide. Check the source and adjust timings for local conditions.

Brussels sprouts (Brassica oleracea Gemmifera Group) are hardy, slow-growing winter vegetables. A mature plant is typically about 90cm (3ft) tall, with a leafy top and a sturdy stem covered in rounded sprouts. Although they occupy the ground for a long season and need generous spacing, only a few plants are required for a useful crop. Modern varieties have a mild, nutty sweetness, and their flavour is often best after frost.

RHS source guide
Brussels sprouts crop illustration

Month by month

Sow

  1. February–AprilIndoors · Modules

    Sow two seeds per module under cover, then thin to the stronger seedling

  2. March–MayOutdoors · Direct sow

    Sow in a seedbed or final position, protecting early batches with cloches or fleece in cold weather

Plant out

  1. May–JuneOutdoors · Transplant

    Harden off module or seedbed plants and set them into firm, prepared ground when 10–15cm tall

Harvest

  1. September–FebruaryOutdoors · Pick

    Harvest firm, tightly closed sprouts from the bottom of the stem upwards, according to cultivar and local conditions

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1 - Getting Started

Brussels sprouts are robust plants, but they take most of the year to mature. Sow from late winter or early spring, plant out in late spring or early summer, and expect to harvest from autumn through winter. Early, mid-season and late cultivars can be combined to extend the picking period. Frost usually makes the sprouts sweeter.

Choose a sunny site with fertile, well-drained soil. The plants become tall and top-heavy, so shelter from strong winds is valuable. Good spacing lets light and air reach the whole stem and helps reduce disease. Fit Brussels sprouts into a crop-rotation plan with other brassicas, avoiding ground recently used for cabbage-family crops where possible.

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2 - Choosing What To Grow

There are more than a hundred Brussels sprout cultivars, as well as related kalettes or flower sprouts. F1 hybrids are widely grown because they tend to produce consistent plants and large, high-quality crops. Early, mid-season and late cultivars can be combined to extend the picking period. Most are green, but purple and red forms such as 'Red Bull' and 'Falstaff' are also available. Compact cultivars are useful in exposed gardens, small plots and containers, while some cultivars offer clubroot resistance or tolerate partial shade.

Seeds are widely available and provide the broadest choice. Young plants are sold in spring and early summer and can save time, although the range is usually narrower.

Recommended varieties

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3 - Preparing The Ground

Brussels sprouts grow best in fertile soil that is firm rather than freshly loosened. Weed the site thoroughly, then improve it with about two buckets of well-rotted manure or garden compost per square metre (or square yard). Autumn preparation is ideal. If the ground is prepared shortly before planting, firm it by shuffling over the surface or treading gently, then rake it level.

Test acidic soil before planting. Where necessary, apply lime during the preceding winter to raise the pH to at least 6.5. This suits brassicas and can help reduce, although not eliminate, the risk of clubroot. Keep lime and fresh manure applications separate rather than applying both together.

On a no-dig plot, spread well-rotted organic matter as a surface mulch and plant through it. Whichever method is used, the final bed should drain freely while retaining enough moisture to support steady growth through summer.

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4 - Sowing

Sowing indoors

Sow indoors from February to April in a greenhouse, cold frame or on a bright windowsill. Modular trays make transplanting straightforward and are especially useful where clubroot is present, because plants can develop a strong, healthy root system before entering affected ground.

Fill modules with peat-free seed compost and sow two seeds in each, about 2cm (3/4in) deep. Germination normally takes a couple of weeks. When both seeds emerge, remove the weaker seedling and retain one plant per module. Keep seedlings in bright light and water regularly, without leaving the compost saturated.

Plants can begin moving outdoors from April once they are at least 10cm tall and have filled their modules with roots. Harden off plants raised in warm conditions before planting them permanently.

Sowing outdoors

Sow outdoors from early March to May. Cover early sowings with cloches or fleece during cold weather. The traditional method is to raise seedlings in a separate seedbed and transplant them in early summer. Sow thinly in drills 2cm deep, with rows 15cm apart. Protect the seedlings from slugs and snails, then thin them to 7.5cm apart.

Alternatively, sow in the final position. Place a few seeds every 60cm, in rows at least 60cm apart, then retain the strongest seedling at each station. Another option is to sow thinly along the row, first thinning to 7.5cm and later to the final 60cm spacing.

For a container, choose a compact cultivar and use one plant in a pot at least 30cm in diameter, filled with peat-free multipurpose compost. Plant a module-raised seedling in early summer, or sow several seeds in the centre and thin to one strong plant.

5

5 - Planting Out

Transplant Brussels sprouts in late spring or early summer when they are 10–15cm tall. Harden off indoor-raised seedlings, and water the seedbed or modules the day before lifting. Handle plants carefully so the root system remains intact.

Set plants slightly deeper than they were growing, with the lowest leaves at soil level. Firm the soil very well around each plant and water thoroughly. Space plants 60cm apart, with at least 60cm between rows. Crowding encourages small sprouts and restricts airflow.

Protect newly planted seedlings from slugs and snails. Install fine insect-proof mesh promptly to exclude cabbage root fly, caterpillars and other pests. Support the mesh on canes or a frame and pin or bury every edge so insects cannot enter underneath.

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6 - Ongoing Care

Brussels sprouts remain in the ground for many months, so inspect them regularly. Remove fading lower leaves to improve airflow and keep the stems accessible. Weed around young plants carefully until the broad foliage shades the soil.

Water young plants regularly and do not allow their root balls to dry out. Established plants usually need additional water only during dry weather, especially in free-draining soil. A thick mulch of well-rotted manure or garden compost conserves moisture and adds nutrients. If growth is slow or the soil is poor, apply a nitrogen-rich feed in June or July.

Firm anchorage is important. In late summer, draw soil up around the base of each stem. Stake tall plants with sturdy bamboo canes, particularly on exposed sites. Keep insect-proof mesh in place throughout the vulnerable growing period and check that it has not torn or lifted.

Container plants dry out faster than plants in open ground. Check the compost often, water whenever the upper layer begins to dry, and feed during the growing season according to the product instructions.

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7 - Harvesting

Early cultivars may be ready from September, while the main crop is gathered through autumn and winter into late winter. Sprouts form in the leaf axils, beginning at the base of the stem. Harvest when they are about walnut-sized, firm and tightly closed.

Start with the lowest sprouts and remove them with a sharp downward tug, taking off the lower leaves as you progress. Pick regularly before sprouts open or turn yellow. Some modern cultivars mature evenly enough for the entire stem to be harvested at once, but most are best picked gradually.

After the sprouts are finished, cut and cook the leafy top like spring greens. Plants can remain standing in the plot until needed. A whole cut stem can be stood in water for a few days or hung in a cool, frost-free shed or garage for short-term storage.

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8 - Problem Solving

Fine insect-proof mesh is the most useful general defence against caterpillars, cabbage root fly, whitefly and pigeons. Start clubroot-sensitive plants in clean compost so that they develop strong roots before planting out. Rotate brassicas and remove badly affected material promptly.

Common problems

Club root

Roots become swollen and distorted, leaving plants weak, stunted or prone to wilting. Improve drainage, raise acidic soil to a suitable pH and avoid moving contaminated soil between beds. Resistant cultivars and strong transplants can reduce losses.

Problem source

Cabbage caterpillars

Butterfly and moth larvae chew holes in brassica leaves and may leave visible caterpillars and droppings. Exclude adults with securely fitted fine mesh and remove caterpillars by hand when found.

Problem source

Cabbage root fly

White maggots feed on brassica roots, causing seedlings or young plants to wilt and fail. Fine mesh and well-fitted brassica collars help prevent egg-laying near the stems.

Problem source

Cabbage whitefly

Small white-winged insects gather beneath the leaves. They are often not serious, but heavy populations can produce sticky honeydew. Encourage natural predators and remove badly affected leaves.

Problem source

Flea beetles

Tiny beetles pepper young leaves with small, round holes. Keep seedlings growing steadily and cover them with fine mesh or fleece immediately after sowing or planting.

Problem source

Mealy cabbage aphid

Grey-green, waxy aphids form colonies on brassicas and can damage young growing points or contaminate the edible crop. Check curled leaves and shoot tips regularly and preserve natural enemies.

Problem source

White blister

This foliar disease causes white blister-like patches and can reduce vigour or distort growth. Remove affected material and avoid wetting foliage unnecessarily when watering.

Problem source

Pigeons

Birds peck and tear leaves, sometimes leaving only stalks and veins. Protect plants with secure netting or fine mesh held clear of the foliage.

Problem source

Slugs and snails

Seedlings and soft young growth can be eaten rapidly. Check shelters and damp areas, protect transplants, and use several compatible control methods where damage is persistent.

Problem source