Boerenkool

Brassica oleracea var. sabellica

Engels: Kale

vegetableBrassicaceaeEetbaar

Boerenkool (Brassica oleracea var. sabellica) is a edible vegetable from the Brassicaceae family that grows up to 80cm tall. This plant thrives in full sun to partial shade and requires moderate maintenance. Attracts butterflies.

Hoogte

40–80 cm

Breedte

30–50 cm

Zonligging

full sun, partial shade

Waterbehoefte

moderate

Grondsoort

loam, clay soil

Onderhoud

moderate maintenance

Ecologische waarde

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Verzorgingskalender

Taak	Jan	Feb	Mrt	Apr	Mei	Jun	Jul	Aug	Sep	Okt	Nov	Dec
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Care tips

Planting

Kale thrives in full sun or partial shade and prefers loam or clay soil that holds moisture well but doesn't become waterlogged. Before planting, prepare the soil by digging in plenty of well-rotted compost or manure; brassicas are hungry feeders and benefit from fertile ground. The soil should be firm rather than fluffy—tread it down gently after digging to give the plants a stable base. Sow kale outdoors from May through July for harvests from autumn through winter. You can sow directly into the ground or start in modules or a seedbed for transplanting later. If sowing direct, place seeds 1–2 cm deep in rows 40 cm apart, then thin seedlings to 40 cm spacing once they have a few true leaves. For transplants, sow in modules and move young plants to their final positions when they're around 10–15 cm tall, spacing them 40 cm apart in all directions. Plant firmly, burying the stem up to the first set of true leaves to encourage a strong root system. Water thoroughly after planting to settle the soil around the roots. If your garden is exposed or windy, consider staking taller varieties later in the season to prevent them toppling over in winter gales. Apply a mulch of compost around the base of each plant a few weeks after planting to suppress weeds and retain moisture. Protect young plants from pigeons and cabbage white butterflies with netting or fleece from the outset—brassicas are magnets for these pests.

Pruning

Kale doesn't require formal pruning in the way a shrub or fruit tree does, but regular harvesting and leaf management are essential for a productive, healthy crop. The key is to pick leaves frequently rather than waiting for the plant to finish growing. Begin harvesting from October onwards, once the plants are well established and at least 20–30 cm tall. Always pick from the bottom of the plant upwards, snapping or cutting off the lower, older leaves first. This encourages the growing tip to keep producing fresh young leaves at the top throughout winter. Take no more than four or five leaves per plant at a time to avoid stressing it. Use a sharp knife or secateurs for a clean cut, which reduces the risk of disease entering through ragged wounds. Remove any yellowing, damaged, or pest-eaten leaves as soon as you spot them, even if they're not ready to eat. Leaving decaying foliage on the plant invites fungal problems and harbours pests like aphids. If your kale bolts prematurely in warm weather—sending up a flower stalk—pinch out the flowering shoot immediately to redirect energy back into leaf production, though once bolting starts the leaves often become bitter. In late winter or early spring, if the plant has become very tall and leggy, you can cut back the main stem by about a third to encourage a flush of tender side shoots, which are delicious steamed or stir-fried. Otherwise, simply keep harvesting until the plant exhausts itself or you need the space for spring crops.

Maintenance

Kale has moderate water needs and dislikes both drought and waterlogged conditions. Water regularly during dry spells, especially from June to August when plants are establishing. Aim to keep the soil consistently moist but not saturated—a good soak once or twice a week is better than daily dribbles. In autumn and winter, rainfall usually provides enough moisture, but check during dry periods and water if the top few centimetres of soil feel dry. Feed kale in June and July with a balanced general-purpose fertiliser or a nitrogen-rich feed to support strong leafy growth. Scatter granular fertiliser around the base of each plant according to packet instructions, then water in well. Avoid feeding later in the season, as this can produce soft growth vulnerable to frost damage—ironic, since kale is famously hardy. Kale is tough and survives hard frosts down to zone 6a without protection; in fact, frost improves the flavour by converting starches to sugars. No special overwintering measures are needed in temperate Europe. Mulch around plants in autumn with compost or well-rotted manure to suppress weeds and feed the soil for next year. Watch for cabbage white caterpillars from May onwards—check the undersides of leaves weekly and squash any eggs or caterpillars by hand. Aphids, particularly mealy cabbage aphid, cluster on growing tips in summer; blast them off with water or use an insecticidal soap. Clubroot is a serious soil-borne disease affecting brassicas; prevent it by rotating crops and liming acid soils to raise pH above 7. Pigeons are relentless—keep netting in place all season.