Question

I only have a small vegetable plot, so can’t follow crop rotation guidelines. I have to put brassicas in the same patch every other year. Can I use lime to prevent club root and cabbage root fly?

You don’t have to garden for long before you meet up with the idea of crop rotation. The idea of this is that you do not grow the same crop in the same place every year and that veg are grown in a different area every year, usually in a four-year cycle.

The groups of plants are usually potatoes in plot one, root crops in plot two, beans in plot three and then brassicas in plot four. This works well if you have four, similarly-sized plots and you want to eat all the veg groups. In practice, in modern gardens, it does not quite work. Apart from anything else, different vegetables like different soil: brassicas like clay and carrots prefer sandy soil. But there is sense in following potatoes, which require lots of digging, with root crops, which need the soil dug over, and following beans, which add nitrogen to the soil, with brassicas, which need nitrogen. Beans and brassicas like lime while potatoes prefer an acid soil.

Of course there is no mention of squashes, sweetcorn or salads and these can be fitted in around everything else.

By avoiding growing the same plants in the same place it theoretically avoids the accumulation of pests and diseases and there should be less chance of vital nutrients being deficient. So it makes sense not to grow the same plants every year in the same place. But there are exceptions and we often make a bean trench or have raised beds with sandy soil for carrots.

Because none of us want to use chemicals unless absolutely necessary, if at all, it makes sense to do all we can to avoid problems whether through crop rotation or selecting resistant crops.

But back to the original question; liming the soil will reduce clubroot but it will not do anything against cabbage rootfly. Clubroot is a fungal disease that is present in the soil. It can be moved from one area to another by moving a small amount of soil, on young plants or your wellies. It needs acid soil so liming slows it down but is unlikely to eradicate it. Fortunately there are varieties that will grow in infected soil, – cabbage and now calabrese and cauliflower and Brussels sprout.

So adding some lime on the years that brassicas are planted, is a good idea and I would use organic fertilisers and plenty of organic matter to keep the soil in good heart. Then it should be possible to grow brassicas every other year. I would be scrupulous with hygeine and remove plants as soon as they are harvested.

As a rough example:

Year one

Jan Feb March April May June July Aug Sept Oct Nov Dec

————/Cabbage/summer cauli/Calabrese/Turnip———-/ Pull up and sow broad beans

Year Two

Jan Feb March April May June July Aug Sept Oct Nov Dec

Broad beans—————————/ Salads——–and chicory/ sow green manure (not mustard)

Cabbage rootfly is a pest that will fly from one area to another and lays eggs on the base of the stem. You can help prevent these doing their damage by putting cardboard ‘collars’ around the base of the young plants.