Calabrese

Growth and cropping pattern

Plants can reach about 60cm (2ft) in both height and spread. They first form a central head, usually around 15cm (6in) across, then redirect their growth into smaller side-shoots once that head is removed. Calabrese belongs to the cabbage family, so include it with other brassicas in crop rotations and protect it from the birds and insects that attack those crops.

Seed or young plants

Seeds are widely sold by garden centres and online suppliers, sometimes under the name broccoli. Young plants may be available in spring and save raising seedlings, but the choice of cultivars is usually narrower. RHS Award of Garden Merit plants have performed particularly well in trials and offer a useful starting point when comparing options.

Improving and firming the soil

In the preceding autumn, dig in two bucketfuls of well-rotted manure or garden compost per square metre (or square yard). If preparation is delayed until nearer planting, tread the soil methodically until firm and then rake the surface level. In a no-dig bed, spread organic matter as a mulch and sow or plant through it.

Remove weeds thoroughly so young plants do not compete for water, light and nutrients. Calabrese prefers a soil pH of at least 6.8. Where a soil test shows very acidic ground, apply lime in the winter before planting; raising the pH can also make club root less favourable.

Sowing indoors

From March to April, fill modular trays with moist peat-free seed compost and sow two seeds per module at 2cm (¾in) deep. Modules limit root disturbance when seedlings are planted out. Germination should take a couple of weeks; once seedlings are large enough to handle, thin each module to the strongest single plant.

Grow seedlings in a greenhouse or on a windowsill, keeping them watered. Transplant when they have a sound root system and stand 10–15cm (4–6in) tall. Harden indoor-raised plants before planting and handle the roots gently, as a check in growth can encourage bolting. After April, direct sowing is preferable because calabrese transplants poorly in warm conditions.

Indoor sowing is also useful where club root is present, because plants can establish stronger root systems before entering infected soil. A mid-autumn module sowing can provide a spring crop, but the young plants must overwinter in an unheated greenhouse.

Sowing outdoors

From April to June, sow either in a temporary seedbed or directly into the final site. A seedbed saves main-plot space while large brassicas are small, but later sowings are better made where they will grow because warm-weather transplanting may trigger bolting.

Make a shallow drill 2cm (¾in) deep. In a seedbed, sow thinly at about 7.5cm (3in) apart, or thin the seedlings to that spacing, then move them once they reach 10–15cm (4–6in). For a final-position sowing, place three seeds every 30cm (1ft), thinning each cluster to one plant. Allow up to 45cm (18in) for larger varieties and keep rows at least 45cm (18in) apart. Protect emerging seedlings with insect-proof mesh to exclude pigeons and brassica pests.

Setting plants out

Plant each calabrese slightly deeper than it grew before, bringing the soil surface up to the lowest leaves so the stem is firmly anchored. Space standard plants 30cm (1ft) apart, or larger cultivars 45cm (18in) apart, with 45cm (18in) between rows. Closer spacing produces smaller heads. Firm the ground around every plant and water generously to settle the roots.

Watering

Water young plants regularly until their roots are established. Mature plants usually need additional water only during dry spells, but do not allow them to stall during head formation. A steady water supply reduces stress and the associated risk of bolting.

Mulching and feeding

Apply a thick layer of well-rotted garden compost or similar organic matter around the plants. Mulch conserves soil moisture, suppresses weeds and reduces the frequency of watering. On poor soil, or when growth is slow, apply an organic-based high-nitrogen fertiliser once plants are about 20cm (8in) tall.

Supporting plants

As the main head enlarges, plants may become top-heavy. Draw soil up around the stem base to improve stability and prevent wind from loosening the roots. Tall plants and those on exposed sites may also need a sturdy cane, with the main stem tied in securely.

Protecting the crop

Cover the bed with fine insect-proof mesh supported on hoops or canes and pin its edges to the ground. Keeping the barrier clear of the foliage and securely closed provides the simplest protection against pigeons, cabbage caterpillars, cabbage root fly and other insects.

Cutting the heads

Cut the main head promptly once it reaches the right stage. Smaller heads will then develop from side-shoots, and the young tender leaves are edible too. Inspect plants every few days and remove each side head while the buds remain closed. Regular cutting encourages further shoots and can extend the harvest by up to two months.