Calabrese is a fast-growing and very easy-to-grow crop that is also known as American, Italian or green sprouting broccoli. Growing up to 60cm (2ft) tall, it produces bluish-green heads up to 15cm (6in) in diameter that are harvested in the summer or autumn, depending on the time it is sown.
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Seeds are generally sown between February and June. Sow two seeds per cell of cell trays in a greenhouse or similar environment until April and outdoors from April. Thin to one plant as soon as the seedlings can be handled. Give general purpose liquid fertiliser every week. When rootball is well bound together plant out into fertile garden soil in full sun or very light shade.
Allow 30cm (12in) between plants and 45cm (18in) between rows. Closer spacing will reduce the number of side shoots formed.
Before planting add a high potassium general fertiliser, such as Vitax Q4, at a rate of three handfuls per square metre/yard, or, if manure or other rotted organic matter has been dug in use half amount of fertiliser. From April, seeds can be sown in the open where the plants are to grow; sow three seeds, 2cm (¾in) deep, every 30cm (12in) along the row. When seedlings are large enough to be handled, thin out each ‘station’ leaving one healthy seedling behind.
Cover seedlings and seed beds with fleece to exclude cabbage root fly, removing fleece in May when risk of damage lessens.
Water every 10-14 days in dry periods. Add high nitrogen fertiliser, such as sulphate of ammonia, at 35g (1oz) per square metre/yard when plants about 20cm (8in) tall. Better heads are produced in cooler summers as hot weather can encourage plants to run to seed prematurely – some cultivars resist this tendency better than others.
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 sideshoots, which can be picked regularly over four to six weeks.
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