How to grow sprouting broccoli and best varieties

Broccoli is a deservedly popular vegetable; it's high in fibre and packed with vitamins including C and K, plus calcium and iron. 

Sprouting broccoli, also known as tenderstem broccoli, is a tasty alternative to large-headed calabrese and is versatile to go in anything from pasta to stir fries and salads. It's much more expensive in supermarkets than calabrese, so it's good option if you want to grow your own.

The Which? Gardening magazine researchers have found the tastiest and most-productive varieties.

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How to grow sprouting broccoli: month by month

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Sprouting broccoli

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Broccoli types explained

What most of us call broccoli is in fact calabrese; but search any of the major supermarkets’ online sites for calabrese and you’ll draw a blank. The term isn’t much used in the UK – we just call everything broccoli, but there are several different types. They are all members of the brassica family – Brassica oleracea to be precise. Calabrese is the large-headed type often sold encased in a tight plastic sheath; broccoli is the sprouting type, whether that’s purple, green or white sprouting; Tenderstem is a trademark name for sprouting broccoli (it even has its own website); and then there is Chinese kale, another cultivar of B. oleracea, which has small broccoli-like florets on thick stems with more leaves than sprouting broccoli. You may also come across broccoli raab, or rapini, a turnip relative whose seed is sold as Cima di Rapa, which translates as turnip tops. It’s popular in Italian cuisine and has a slight mustard flavour, slender stems with small florets and lots of leaf. We included it in our trial but it bolted too quickly to provide any harvest.

How to grow

Sowing

Sow the seeds singly in small pots or modular trays, indoors from March or sow direct from April. You can sow in small batches from March to May to prolong the harvest period. Alternatively, buy plug plants if you want only a few.

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Planting

The seeds should germinate in 7-10 days and be ready to plant out a month after sowing. Be sure to harden them off beforehand. Work a balanced fertiliser such as Growmore or pelleted chicken manure into the soil. Take care not to disturb the rootball and push the soil in around the roots firmly, but don’t compress the top of the soil, as this can compact it and prevent water getting to the roots. We spaced our plants 45cm apart each way; closer spacing will reduce the number of side-shoots. 

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Caring for your plants

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

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Harvesting

Harvest in: June to August

Some sprouting broccoli varieties produce a small terminal head and then the smaller side-shoots after this is harvested. 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 shoots regularly when the buds are fully formed. As a precaution, soak your harvest in salty water before cooking to get rid of any caterpillars that may be on them. 

Common growing problems

Leaf spot

There are several fungal leaf spots that attack brassicas causing discoloured spots to develop on the leaves. Remove any infected leaves promptly. 

Clubroot

You can recognise clubroot damage as swollen roots with 'finger and thumb'-like projections are the typical signs. The plants wilt, appear stunted and go grey/blue as their roots are destroyed. They typically recover from the wilting at night. Infected roots soon rot into a foul-smelling mass, discharging spores into the soil.

Galls vary from lumps covering the swollen bulbs on turnips and swedes to finger-like projections on fibrous-rooted brassicas. Some of the most spectacular galls occur on Chinese cabbage and other oriental greens.

Once your plants are attacked, there is no cure. However, you can earth up the plants in the hope that new roots will be formed further up the stem. These roots may then escape infection for long enough for the plants to produce a crop.

Wet and acid soil are the favoured conditions of clubroot. Improving drainage will help. Making raised beds is a good way of doing this. Use treated boards, for example, to make beds 1-1.5m wide and at least 15cm higher than surrounding soil. Acid soils can be made more alkaline and much less prone to clubroot infection by the addition of lime or chalk. Lime is cheap, so this is the most economic way to keep down clubroot.

Cabbage root fly

The first sign of attack is when the foliage turns a blue/red colour and appears stunted. Plants also wilt in hot weather. When you pull a plant, it comes up easily: most of its roots will have been eaten, and they will often be covered in maggot-like larvae. Typically, the fibrous roots will have been destroyed, and sometimes the plant will produce more fibrous roots from the base of the stem.

The maggots are usually too deep in the soil or inside plants for the insecticide to get at them. Earthing up affected older plants will sometimes let them root above the damaged areas, and may save the plants. Giving affected plants plenty of water with some liquid feed may also help overcome the damage.

Closely sown crops in seedbeds, or sown where they are to crop (eg swedes, turnips and radish), can be protected by covering them with horticultural fleece or insect-proof mesh. This should be done before the first hatch of the pests in April. Fleece traps so much warmth that it is likely to ‘cook’ the crop after the end of May. Insect-proof mesh, being more ventilated, is a better option to protect plants after this. Although mesh can be laid straight over the plants, it is best supported on hoops. Make sure it is buried at least 5cm deep all round, as the flies can get in through any gaps. These covers will get young plants safely through the spring attacks, which are often the worst. Transplanted plants can be protected by discs of tarred paper, or, better still, squares of carpet underlay, fitted closely round the base of the stem. These stop the adults laying eggs close to the stem, and protect the plant. Their disadvantage is that putting them on can take a long time, and they will not work if they get blown away by strong winds, moved by the swelling stem of the growing plant or covered in soil when weeding. To make your own barriers, cut squares of rubber carpet underlay or cardboard, about 15cm square, and cut a slit from the edge to the centre. At the centre make a small hole. The hole should fit snugly round the plant's stem. These barriers not only exclude the pest, but act as mulches to keep roots cool and moist, keep down weeds and even shelter the predatory beetles that feed on the cabbage-root fly. Alternatively, use plastic drinking cups with the bottoms cut off and fit them over the plant at planting-out time. Push them into the soil so the plastic will stop the insects getting close to the plants.

Caterpillars

Caterpillars strip foliage, tunnel into the hearts of cabbages and spoil produce with their droppings or frass. There are two cabbage-white butterflies that do serious damage: the large white and the small white. Damage is also caused by moth caterpillars.

Large whites emerge in the spring and seek out cabbage plants, laying as many as 200 eggs in clumps beneath the leaves. Two weeks later, the eggs hatch and caterpillars emerge. They feed in a colony at first then disperse, but not far, so if you find one, you will find others. Once fully grown, they pupate away from plants, soon hatching into butterflies. The second generation in July and August are numerous and very damaging.

The small white is similar, emerging a little earlier in the spring, laying eggs and producing caterpillars that feed singly. The chrysalids form on the plants. There is also a second generation of small whites, which cause damage into the autumn. The second generation of both types will not hatch until spring.

Cabbage moths are on the wing at night during May and June, laying batches of round eggs on the leaf undersides that will hatch after two weeks. The caterpillars feed for at least a month before they mature. They pupate in the soil and generally hatch the following spring. But a few will hatch in late summer and into the autumn. They can be found in early winter if it’s mild. The chrysalids of the second generation hatch in the spring.

Once the caterpillar is inside the heart or head, it is almost impossible to kill. Treat early, before the pest has a chance to get inside. Once caterpillars are inside, salvage whatever leaves you can by cutting out the damaged parts. The best way to avoid attack is to grow your plants under insect-proof mesh. Otherwise, inspect them regularly and squash any eggs or caterpillars you find. Alternatively, you can spray with the caterpillar.

How we test broccoli

We sowed our broccoli in mid-March in large modules filled with a Best Buy peat-free compost. The seedlings were grown on until planting out in mid-May. Harvesting of the earlier varieties began in the last week of June. We picked side shoots from our plants twice a week, recording the number and weight for each variety. We assessed the quality of the shoots and tasted all the varieties both raw and lightly steamed.