The vegetable we grow can be grouped into several plant families which have similar characteristics and often suffer from the same pests of diseases. Crop rotation is where we grow vegetables from each major plant family in different areas each year.
Reasons for crop rotation
- Pests and Diseases. Several problematic pests and diseases can build up in the soil if the plants they affect are grown in the same area each year. For example, nematodes such as eelworm can devastate potato crops grown in the same place every year. It can also affect other vegetables in the same crop family such as tomatoes. Onion rot is a serious fungal disease that can persist when crops from the allium group are continuously grown. Cabbage root maggots affect all brassica crops. Fusarium root crop can wreck pea and bean harvests. These are just a few of the many soil-borne pests and diseases and crop rotation is almost universally recommended to prevent them all.
- Avoiding Soil Nutrient Depletion. Different vegetables take different balances of nutrients from the soil and their roots access different levels of the soil structure. Cabbage family plants like a lot of nitrogen, tomatoes need plenty of calcium, beets and beans require manganese, and so on. Salad crops are shallow-rooted, but other vegetables have roots that extend deep into the soil to bring up nutrients from those layers. Because of this, growing the same vegetable in the same place every year can lead to nutrient deficiency and poor growth.
- Suppressing Weeds. Some plants, like potatoes, act as a good clearing crop, that is, their dense foliage helps to suppress weed growth, and when they’re dug up, birds can eat pests in the soil such as slugs and wireworm. Squash or leafy greens can also be used to suppress weed growth before growing a crop like onions or carrots which are highly susceptible to competition from weeds.
Crop rotation is an essential part of growing vegetables well. However, just knowing that we should rotate crops doesn’t make it easy to organize. After a few seasons, crop rotation can become very complex, even in relatively small gardens.
To rotate crops, you need to remember all the crops grown in the past and you need to be able to correctly identify which plant family they belong to. Some references suggests that having one bed for cabbage family plants, one for beans, one for potatoes, etc, and then rotating them each year. Some gardeners want to grow equal areas of each crop type so this isn’t always practical and there are often additional constraints such as whether your climbing beans will cast shade over other plants.
There are also recommendation which is very simple like placing root vegetable, fruiting vegetables, and leafy vegetables in different areas. But this system doesn’t work well. It is not a good idea to grow tomatoes (a fruiting plant) after potatoes (a root crop) because both are in the same crop family and suffer from similar pests.
Recording your crops and knowing the plants family is very important in effective crop rotation. There are smart phone applications that can be downloaded for crop rotation, download and use it.