Buying winter seeds for vegetable growers is an exciting time, just like them plan their cultivation for 2025. It can be difficult to fit everything in, and that’s where a crop rotation plan can help.
Crop rotation sometimes causes anxiety among vegetable growers, but it simply means not growing the same crop in the same place for three or four years.
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A typical crop rotation in the garden can last three years, with the plot divided into three sections, with potatoes and tomatoes grown for one year. The following year that part is planted with peas, beans, root vegetables, onions, leeks and most other vegetables, followed in the third year by cabbage family crops such as Brussels sprouts.
Where fewer potatoes or cabbage family crops are grown, a four-course rotation can be followed with a separate year for peas and beans or for the onion family.
Each of these groups has different problems. Potatoes and tomatoes suffer from potato cyst nematode and potato (and tomato) blight, the spores of which may persist from year to year in the soil. Onions, leeks, garlic and shallots are vulnerable to root fungal disease and downy mildew spores can survive for several years. Cabbage family plants can be attacked by root fungus, while peas and beans are susceptible to several wilt and foot rot diseases whose spores can remain in the soil for years.
Unfortunately, the spores or cysts of tuberous root, white rot and potato cyst nematodes can remain viable for more than 10 years. Other diseases, such as downy mildew, produce ‘dormant spores’ that can survive for up to five years. Rotations are less useful on unwanted insects such as carrot fly. Winged insects can fly or float on water breeze over a mile to find new hosts. Some diseases, including downy mildew and late blight, have small spores that can travel significant distances.
Agricultural rotations where more land is available typically last five years or more, which is very effective.
Nevertheless, crop rotation in the garden delays the arrival of diseases on new plots and slows the build-up of infectious material in the soil.
Crop rotation can also help with weed management. For example, onions and carrots have leaves that cast little shade and do not compete with weeds. Potatoes, pumpkins and pumpkins have extensive foliage that smothers weeds, so rotating crops with different habits provides more press on weeds.
Crop rotation also helps with weed management (Photo: Tim Sandall)
Different crops also have different nutritional requirements that they obtain from soil minerals. Changing crops annually can reduce the chance of plants becoming deficient.
However, gardeners who choose not to practice crop rotation may not immediately notice that their crops are being harmed. Indeed, some gardeners find it more convenient to grow the same harvesting in the same place year after yearand only move it to a new location if problems arise.
This is particularly common in vegetable gardens which are much smaller than traditional allotments and may consist of a few square meters of raised beds. Formal crop rotations are rarely feasible on these plots. Fortunately, growing the same crop in the same place year after year can work very well for years. This may be due to the soil being ‘oppressive’. where soil microbes are antagonistic Problematic organisms are present, which suppress disease to a significant extent. No-dig regimes are more likely to develop ‘suppressive soils’ because they add very significant amounts of organic matter each year, which promotes the abundant growth of soil microbes.
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