Calabrese is a very easy, fast-growing crop, also known as American, Italian or green sprouting broccoli. Reaching 60cm (2ft) tall, it produces bluish-green heads up to 15cm (6in) across that are harvested in summer or autumn, depending on sowing time.
Jobs to do now
- Make your final harvests
Month by month
Seeds are generally sown between February and June – indoors from late winter into spring, then outdoors through to early summer.
From Febuary to April, start seeds off in a greenhouse or indoors. Sow into a modular tray filled with seed compost, two seeds per module. As soon as the seedlings are large enough to be handled, thin to one per module. Give them a general purpose liquid fertiliser every week.
From April, sow in the ground where the crop is to grow. Choose a sunny or very lightly shaded spot, with fertile, well-drained soil.
Sow three seeds, 2cm (¾in) deep, every 30cm (1ft) along the row. When the seedlings are large enough to handle, thin out to leave just one healthy seedling every 30cm (1ft).
Cover the plants with fleece to exclude cabbage root fly, removing it in May when the risk of damage lessens.
Water every 10–14 days during dry periods.
When plants are about 20cm (8in) tall, apply a high nitrogen fertiliser, such as sulphate of ammonia, at 35g (1oz) per square metre/yard.
Better heads are produced in cooler summers, as hot weather can encourage plants to go to seed prematurely – some cultivars resist this tendency better than others.
When indoor-raised plants have formed a good rootball, transplant them out into fertile soil in full sun or very light shade.
Prepare the ground by adding a high potassium general fertiliser, such as Vitax Q4, at a rate of three handfuls per square metre/yard. If the soil has been enriched with garden compost or well-rotted manure, use only half the amount of fertiliser.
Space plants 30cm (1ft) apart, with 45cm (18in) between rows. Closer spacing will reduce the number of side-shoots produced.
Birds, especially pigeons, can cause an array of problems including eating seedlings, buds, leaves, fruit and vegetables.
Protect the plants from birds by covering them with netting or fleece. Scarecrows and bird-scaring mechanisms work for a while, but the most reliable method of protection is to cover plants with horticultural fleece or mesh.
A number of caterpillars will feed on brassicas, but the most common are those of cabbage white butterflies. You will usually see the caterpillars, if not, you will see the holes they make in the leaves. They will also bore into the heart of cabbages.
In mild attacks, or if you have only a few plants, you may be able to pick the caterpillars off. Insect-proof mesh or fine netting (5-7mm mesh) can prevent egg-laying.
Roots become swollen and distorted, and leaves become pale and yellow and wilt easily. Plants may die.
Improve drainage and add lime to make soil more alkaline. Do not grow in affected soil.
Calabrese can be harvested from late summer into autumn.
It is ready to harvest when the flower shoots (spears) are well formed but still in bud, before individual flowers begin to open.
Cut the central spear first. This is followed by a series of side-shoots, which can be picked regularly over four to six weeks.
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