One of the great things about having a polytunnel is that you can easily grow brassicas all year round. While these crops can also often be grown outside, a polytunnel makes it easier to grow different forms of broccoli since it is easier to curtail loss to pests such as slugs and snails, and pigeons and other birds. A polytunnel can also be a useful place to sow broccoli prior to transplanting it to its final outdoors growing position. Calabrese is the type of broccoli with a large head that we are used to seeing in the summer months but there is also a range of other types of broccoli for over-wintering that sprout smaller heads in spring. Most broccoli is treated as an annual crop, though a perennial variety is also available.
Whenever they are harvested, broccoli is always sown in spring and planted out after all risk of frost has passed – a polytunnel can give you an earlier crop of calabrese broccoli than it is possible to get outside. Seedlings should be sown in a seed bed or in pots at a planting depth of around 1cm and can be transplanted to their final growing positions when they are around 7cm high.
It is a good idea to sow broccoli and calabrese in a frost-free but cool position and if they have been indoors, they will have to be hardened off before they make their way outside. Plant transplants deeper than they were in pots and firm the soil well around them. Water in well and keep watered during dry periods. Broccoli and calabrese will also appreciate a high nitrogen organic mulch.
Calabrese broccoli should be spaced 40-60cm apart. The wider this distance, the larger the heads you will be able to achieve. Sprouting broccoli for spring harvest can be planted out at a spacing of 30-40cm. Companion planting may help to achieve higher yields. Alliums, for example, and herbs such as basil and thyme, can deter some common pests. Legumes may help with nitrogen requirements. Lettuce can be intercropped and harvested before the broccoli needs the space. Beetroots are said to be another good companion for broccoli.
Calabrese broccoli can be ready for harvest from July-August. Cut off the heads when these have developed good size and shape but before the flower buds have begun to open. Do not lift the plants after harvesting the first heads – leave them alone and smaller secondary heads will form that can also be harvested. Sprouting broccoli will overwinter and can be a good crop to fill the gap between Brussels sprouts and cabbage in the spring. A perennial broccoli will last around 5 years or so and can look wonderful in a mixed border or in a perennial section of your polytunnel. Perennial vegetables can be a low-maintenance alternative to traditional annual crops.
Sowing time – April to May
Planting time – June to July
Expecting cutting time – August to October
Early varieties February to April