Q How do I sow calabrese?

A Sow the seeds singly in small pots or modular trays, as the plants don’t like root disturbance. Sow them in small batches from March to May if you want a succession of harvestable heads, although stem varieties crop over a longer period. If you only want a few plants, buy them as plug plants.

Caption: Calabrese is packed with vitamins and iron

Q How do I plant calabrese outdoors?

A The seedlings should be ready to plant out a month after being sown, but harden them off for around a week before planting out. Before planting out, fork in a balanced fertiliser such as Growmore or pelleted chicken manure.
As you plant take care not to disturb the rootball, as that can cause them to flower prematurely. Push the soil in around the roots firmly, but don’t compress the top of the soil, as this can compact it and stop water getting to the roots.

We spaced our plants 30cm apart, in rows 45cm apart – a compromise for a good crop of calabrese heads and side-shoots. Closer spacing will give large main heads but fewer side-shoots.
In previous research for Which? Gardening magazine, we tried increasing the spacing to 45cm each way, which boosted the average total yield.

Give plants a good soaking once a week in dry spells.

Caption: Plant calabrese firmly but don't compress the top of the soil

Q How should I harvest calabrese?

A With most varieties of large-headed calabrese you get two crops from a single plant. Initially, a central dome will form, after this is harvested the plant will produce numerous smaller side-shoots. 
Coming up to harvest time, check the plants at least twice a week, as the tight green buds may quickly open into yellow flowers, ruining your crop. Some varieties last longer before bolting, so grow these if you want to avoid gluts. However, temperature, rainfall and time of year can all affect how long the plants will last before starting to form flowers.
Pick the main heads and side-shoots when the buds are fully formed. As a precaution, soak your crop in salty water before cooking to get rid of any caterpillars that may be on them.

Caption: Harvest the main head of calabrese first

Q Which pests and diseases affect calabrese?

A Calabrese attracts many flying pests including aphids, cabbage whites, flea beetles, root fly and pigeons. Keep these off your crops by covering plants with a fine mesh when you plant out.
There are several fungal leaf spots that attack brassicas causing discoloured spots to develop on the leaves. Remove any infected leaves promptly.
Clubroot is caused by a soil-born slime mould that causes swelling and distortion of the roots leading to wilting foliage, poor growth, discolouration and very poor cropping. There’s no way to save infected plants, so immediately remove any you find. Don’t compost them, to help prevent the disease reoccurring.