Crops in focus: brassicas

Which are what most people are harvesting now. I still have exactly one floret of purple sprouting broccoli, so I hope the rest hurries up a bit. First to clarify a confusion: broccoli is an over-wintered crop but calabrese produces its crop the same year, before the winter. Both are brassicas as are cabbage, kale and cauliflower - and they are all part of the mustard family, oddly enough.

The ideal brassica bed needs both nitrogen and humus so the addition of manure in autumn will accomplish both. Dig over the soil and then add a barrow load of manure per square metre to the land. Leave the manure over the winter to give the worms a chance to take some down into the soil. But because adding the manure will have had the effect of making the soil more acid and because brassicas don’t like acidity, it’s best to test pH to measure the acidity and add the appropriate amount of lime to take the level up to 7.0.

Seeds are usually sown in spring, planted out in early summer to give a crop the following February/March through to May. There are early, mid-season and late varieties if you want a long harvest. Wind rock can damage the plants, especially through the winter, so try to find a sheltered site, earthing up around the stems for several inches keeps the plant stable and you may want to stake the tallest varieties – we certainly do!

You’ll also want to keep them netted, pigeons will go for the young plants especially in winter when other food is scarce. Broccoli is a slow-growing crop and it may benefit from a liquid feed, high in nitrogen, in the spring as the heads begin to form.

All brassicas are at risk of clubroot, caused by a soil borne organism which produces cysts which lurk in the soil until a suitable host is available to infect, starting the cycle again. The cysts can live for 8 or 9 years. Even worse, it is easily spread. The first sign is a wilting of plants, especially in dry weather. The roots have swellings and look knobbly. If you have a clubroot problem - start your brassicas off in modules using sterile compost to which you’ve added a small amount of lime – keep potting on until they reach 5 inch pots. Clubroot thrives best in acid wet soils so ensure your brassica bed is well dug with grit or other material to allow free drainage and take the pH up to 7.5 or even as high as 8.5 by adding lime Before planting, dig a hole at least 30cm deep and wide which you dust with lime to whiten the soil in the hole. Fill the hole with bought in multi-purpose compost and then plant your brassica in this. And burn your brassica plants when you’ve harvested, so you don’t return any clubroot to the soil.

Labels: allotment-brassicas, allotment-broccoli, allotment-crops