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Kale

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

Month by month

Sow

  1. March–June

    Sow indoors in modules or outdoors in a seedbed or final position.

  2. Any month indoors

    Sow densely on a bright windowsill for microgreens.

  3. Spring–summer

    Make small repeat sowings for baby cut-and-come-again leaves.

Plant out

  1. Late spring–early summer

    Transplant hardened plants once they reach 10–15cm (4–6in) tall.

Harvest

  1. September–spring

    Pick mature lower leaves little and often.

  2. Year-round from indoor sowings

    Cut microgreens after two to three weeks.

  3. Spring onward

    Harvest salad leaves once rosettes reach 10–15cm (4–6in).

1

1 - Getting Started

Kale is one of the hardiest cabbage-family vegetables, providing nutritious leaves through autumn, winter and spring. Mature plants may reach 90cm (3ft), while compact cultivars suit pots and small plots. Leaf shapes range from smooth and puckered to densely frilled, with green, blue-green, purple or red colouring and contrasting veins or stems. Curly kale is also called borecole.

Young plants can be grown as a quick cut-and-come-again salad, while mature leaves are harvested for cooking over many months. Regular picking encourages new growth. Kale is normally biennial, producing foliage in its first season and flowering in its second, although perennial heirlooms also exist. It is ornamental enough for productive borders as well as the vegetable plot.

2

2 - Choosing What To Grow

Choose leaf texture, colour, ultimate size and intended use. Narrow puckered Tuscan forms differ markedly from tightly curled borecoles. Compact cultivars work in containers; tall sturdy ones provide a large winter crop but may need support. Red and purple leaves are especially attractive as baby leaves or microgreens.

Recommended varieties

3

3 - Preparing The Ground

Kale prefers rich, firm, well-drained soil, although it tolerates most soil types and light shade. Weed thoroughly and incorporate plenty of well-rotted manure or garden compost, then rake level and firm the bed. In a no-dig system, add organic matter as a surface mulch and sow or plant through it.

Rotate kale with other brassicas to slow the build-up of soil-borne problems. Where club root is present, raise transplants in clean compost until they have a stronger root system, or use containers filled with fresh peat-free compost.

4

4 - Sowing

Sowing indoors

Start from March in modular trays, which minimise root disturbance and protect seedlings from slugs, snails and infected garden soil. Fill cells with peat-free multipurpose compost and water. Make a 1cm (½in) hole in each cell, sow two seeds, cover, then keep moist in bright light. If both germinate, retain the stronger plant.

Sowing outdoors

Sow from March to June in a firm prepared seedbed or directly in the final position. Make a 1cm (½in) drill and water its base if dry. In a seedbed, sow thinly at 10–15cm (4–6in) or thin seedlings to that spacing. Transplant after six to eight weeks.

For final-position sowing, place three seeds about every 45cm (18in), adapting the distance to the cultivar: allow 60cm (24in) for large kale and 30cm (12in) for compact plants. Thin each station to one strong seedling and keep rows at least 45cm (18in) apart.

For baby salad leaves, sow directly about 7.5cm (3in) apart in repeat batches. In containers, scatter salad seed thinly and cover with 1cm compost. For one mature compact plant, use a pot at least 30cm (12in) wide and deep, sow three seeds at the centre and thin to one.

Microgreens

Sow densely on damp peat-free seed compost on a sunny windowsill at any time. Water regularly and cut the seedlings after two to three weeks.

5

5 - Planting

Move young plants in late spring or early summer once they are 10–15cm (4–6in) tall. Harden off indoor-raised seedlings first. Lift carefully or remove the intact module, then plant more deeply than before with the lowest leaves at soil level. Firm thoroughly so the developing top-heavy plant is well anchored, and water in.

Space mature plants 30–60cm (12–24in) apart according to size. Good airflow and light reduce fungal disease and support reliable cropping. Baby-leaf plants can remain about 7.5cm (3in) apart. Cover immediately with fine insect-proof mesh and protect young plants from slugs and snails.

For container crops, use peat-free multipurpose compost. A 30cm-wide and deep pot holds one compact mature plant; baby leaves can be planted closer. Position in sun and keep compost evenly moist.

6

6 - Plant Care

Weed regularly and remove faded lower leaves to preserve airflow and discourage fungal problems. Water seedlings and young transplants before soil dries out. Established ground-grown plants usually need water only during prolonged dry spells, while containers require regular checking through summer.

Mulch mature kale with a thick layer of well-rotted manure or garden compost to hold moisture and suppress weeds. Feeding is usually unnecessary in prepared ground, but poor soil or pots may benefit from an organic nitrogen-rich fertiliser.

Tall varieties can become top-heavy. In autumn, add sturdy bamboo canes in exposed places so winter gales do not loosen their roots. Keep insect-proof mesh supported clear of the foliage on hoops or canes, and secure its edges against pests and pigeons.

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7 - Harvesting

Mature kale is generally ready from September. Take two or three of the lowest healthy leaves from each plant at a time, leaving the central growing point intact. Frequent moderate harvests stimulate fresh leaves and extend the crop through winter and into spring.

For baby salad production, begin when plants reach 10–15cm (4–6in). Pick individual leaves from several rosettes or cut a whole rosette above its growing point so it can resprout. Remove yellowed or damaged foliage rather than leaving it around the plant.

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8 - Problem Solving

Kale is robust and winter hardy but shares the pests and diseases of other brassicas. Rotation, firm healthy transplants, wide spacing, clean cultivation and fine-mesh protection prevent many losses. Inspect undersides of leaves and the plant's centre regularly.

Common problems

Club root

Affected plants become stunted or wilt, with swollen distorted roots. Avoid moving contaminated soil, use clean transplants and lengthen brassica rotations.

Problem source

Cabbage caterpillars

Larvae of several moths and butterflies chew foliage, contaminate plants and may strip leaves. Check regularly and use supported insect-proof mesh.

Problem source

Cabbage root fly

White maggots feed on roots, causing poor growth or collapse. Protect young plants with close-fitting collars or mesh and firm transplants well.

Problem source

Cabbage whitefly

Small white-winged insects gather beneath leaves. Established plants often tolerate them, but large colonies and sticky deposits reduce crop quality.

Problem source

Flea beetles

Small beetles create many round holes, with seedlings most at risk. Keep plants growing steadily and protect emerging crops with fine mesh.

Problem source

Mealy cabbage aphid

Grey-green waxy aphids form dense colonies, distort young growth and can make leaves unusable. Encourage predators and remove badly colonised leaves.

Problem source

White blister

Raised white pustules and distorted foliage indicate this disease. Remove affected material and improve airflow by avoiding overcrowding.

Problem source

Pigeons

Birds tear leaves and may leave only stalks and main veins. Keep kale under securely anchored mesh through vulnerable periods.

Problem source

Slugs and snails

These molluscs attack seedlings and tender leaves, especially in damp shelter. Reduce hiding places, encourage predators and protect young plants.

Problem source