When to plant Brussels sprouts

Brussels sprouts need a long season: roughly five months or more from sowing to the first sprouts. Sow from March to April, indoors in modules or outside in a seedbed, and plant out from mid-May to June.

Timing matters more than with most cabbages. Plant too early and the sprouts tend to stay loose; plant too late and they stay small. Early varieties are ready from about September or October, while the frost-hardy late ones, which need up to eight weeks longer, crop through winter.

For a long harvest, grow an early and a late variety side by side rather than sowing several times.

Sow 0.4–0.8 in deep, a couple of seeds per module or thinly in a seedbed row, and keep the strongest. Seedlings appear in one to two weeks. Plant out when they are 4–6 in tall.

Sprout plants grow 30–35 in tall and stand through winter storms, so they need a firm footing. Prepare the bed well ahead with about two buckets of compost per square metre, lime acid soil to a pH of at least 6.5, and tread it firm before planting.

Set the plants deep, up to the lowest leaves, firm them in hard and water well. Space them 24 in apart with 24 in between rows; closer planting gives smaller sprouts. That is a lot of room: a 120 × 80 cm raised bed only takes two or three plants, so sprouts are better suited to open ground.

Keep young plants watered and never let them dry out while they establish. In late summer, draw soil up around the base of the stems; tall varieties on exposed sites may also need a stake.

Sprouts are Starkzehrer, heavy feeders, but too much nitrogen does harm: the plants grow soft and top-heavy and the sprouts come out loose. On poor soil, give one nitrogen-rich organic feed in June or July and leave it at that.

Some growers pinch out the top of the plant once the lowest sprouts are forming. That makes the sprouts up the stem size up at the same time, useful if you want to pick a whole stalk at once. For picking a few at a time through winter, leave the top on.

Start at the bottom of the stem, where the sprouts ripen first. Pick them when they are firm, tightly closed and about walnut size, 1–1.6 in across, by snapping them off with a sharp downward tug. Work your way up the stem over the following weeks.

The season runs from about October to February, with the main harvest in November and December. Early varieties can start in September.

Sprouts do taste sweeter after cold weather, and that is why many gardeners wait for the first frosts. As with kale, it is the cool spell that counts, not the frost itself.

The plants are hardy in most of Central Europe and the UK. Repeated frosts below about 14°F damage the sprouts.

Choose one early and one late variety for a long season. The late, frost-hardy varieties take up to eight weeks longer to crop. Red-leaved varieties such as 'Red Bull' look striking in the bed.

If your soil carries clubroot, the resistant F1 varieties 'Crispus' and 'Cryptus' are worth growing.

Sprouts stand in the ground for most of a year, so they meet every cabbage pest. Cabbage root fly maggots kill young transplants in late spring and, later in the year, can tunnel into the sprouts themselves. A collar 3–6 in across fitted snugly around each stem at planting keeps the first generation away.

Cabbage white caterpillars feed from about May to October. Check the leaf undersides every week and squash egg clusters, or keep the butterflies out with mesh. Insect mesh laid right after planting works against caterpillars and root fly with holes of about 1.3 mm, and against flea beetles and mealy aphids at 0.8 mm. On tall sprouts it needs a frame or hoops.

Mealy cabbage aphids and cabbage whitefly are typical of sprouts and kale, whitefly especially in warm, dry late summers. Hose the undersides of the leaves, and clear old stalks in spring, because whitefly overwinters on them. In the UK, pigeons strip plants in winter; netting keeps them off.

Clubroot turns the roots into solid, swollen clubs; plants wilt on warm days and stay stunted. Spores survive in soil for many years, up to 20. Lime to around pH 7, raise plants in pots, bin infected roots, and wait at least four years before cabbage-family crops go back, seven or more after an outbreak.

Brussels sprouts are in the cabbage family (Brassicaceae), with cabbage, kale, broccoli, cauliflower, kohlrabi, radishes, turnips and rocket. All count for rotation, including mustard as a green manure.

Mixed-planting charts suggest partners for sprouts such as celery, lettuce, spinach or beans. We found no solid evidence for these; treat them as tradition.

The companion idea with research behind it: a low undersowing of clover makes brassicas harder for cabbage root fly to find, and mixed plantings in general tend to have fewer pests than a single crop.