Broccoli

Light and exposure

Broccoli wants sun, but it does not crave heat the way a tomato does. A sunny to lightly shaded spot suits it, with at least five to six hours of light a day. In a cool temperate climate, full sun does not bother it, provided the soil stays cool underneath.

Avoid hot, dry spots against a wall that takes the full midday sun, where it would bolt too quickly in strong heat. An open, well-aired corner of the vegetable garden also limits the leaf diseases that a humid summer encourages. Air circulation matters as much as light.

Watering

It is a drinker. Broccoli needs a soil that stays cool at all times, especially when the head is forming. Water stress at this stage gives small, loose heads that bolt before their time. Water regularly and generously, at the base, preferably in the morning.

In a temperate climate, summer often brings rain, but not always at the right moment. During the dry spells of high summer, a generous watering two to three times a week is better than a daily trickle. A good mulch of dried grass clippings or straw keeps the moisture in and stops the soil from drying out between showers.

Soil and repotting

Broccoli demands a rich, deep soil well supplied with nitrogen. Prepare the spot in autumn or early spring with a good dose of mature compost or well-rotted manure. Poor soil gives puny plants and disappointing heads.

It likes rather heavy, cool soils, which makes it one of the few vegetables genuinely at ease in clay ground. A neutral to slightly limy pH suits it, around 6.5 to 7, and also limits clubroot. If your soil is acidic, an application of lime a few months before planting is useful. Still, ensure proper drainage, because standing water through the cold season is not its friend.

Temperature and humidity

Broccoli is a cool-season vegetable. It grows best between 15 and 22 degrees and easily takes cool spring and autumn nights. Young plants tolerate light frosts, and a well-established plant takes a few degrees below zero at the end of the season.

Heat, on the other hand, presses it: above a sustained 25 degrees, it tends to bolt too early and open its head prematurely. In a mild temperate climate this risk stays moderate, but during summer heatwaves, generous watering and a little shade help it hold on. That is exactly why autumn harvests are often the finest there.

Pruning and upkeep

You do not really prune broccoli, you harvest it at the right moment, which comes down to managing the plant. Cut the central head when it is well formed and still tight, before the little buds turn yellow. A head that starts to flower is past its point, it stays edible but loses flavour and texture.

After this cut, do not pull the plant out on any account. Leave it in place and keep watering it: it will produce a series of side shoots, mini-heads in the leaf axils. They are smaller but just as good, and this regrowth extends the harvest by several weeks. Pick them regularly to encourage the plant to make more.

Pests and diseases

Cabbages pay a heavy tribute to pests, and broccoli is no exception. The cabbage white, that white butterfly, lays on the foliage and its green caterpillars devour the leaves; inspect the underside of the leaves and remove the eggs by hand, or fit an insect net right from planting. The cabbage root fly lays at the collar and its larvae attack the roots, a cardboard collar at the base of the plant discourages it. Flea beetles riddle young leaves with little holes in dry weather, and slugs love freshly transplanted plants.

As for diseases, clubroot is the most feared in damp, acidic soils: a soil fungus that deforms the roots into galls and makes the plant waste away. It persists in the soil for years, hence the crucial importance of rotation. Never replant a cabbage, turnip or radish in the same spot before three or four years. A well-drained soil that is not too acidic also limits its establishment.

Propagation

Broccoli is propagated by seed, the only practical way. Sow warm, between 15 and 20 degrees, from the end of winter onwards, in a seed tray or pots under cover. Emergence is quick, four to seven days. Then prick out the seedlings into individual pots as soon as they have two or three true leaves.

Plant out in the garden when the plants are about fifteen centimetres tall and the risk of hard frosts has passed, spacing them generously by 50 to 60 centimetres, because an adult broccoli is bulky. Set them a little deeper than in the pot, up to the first leaves, for better anchorage. Saving your own seed is possible but tricky, because cabbages cross easily between varieties and are biennial; for a family garden, it is better to buy seeds or plants.

Month-by-month care calendar

Green Hub tips

• Cut the central head nice and tight, before the buds yellow, then leave the plant in the ground: it makes side shoots again for weeks.
• Never replant a cabbage in the same spot two years running. Rotation over three or four years is your only real defence against clubroot.
• An insect net fitted right at planting settles the cabbage white and the cabbage root fly in one go, without spraying anything.
• Never let the broccoli go thirsty when the head is forming: one dry spell and it bolts before its time.
• Autumn harvests are often the best in cool climates: the coolness gives firm, tightly packed heads.