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Crop rotation to avoid disease in the vegetable patch

Val Bourne / 26 February 2018

Gardening expert Val Bourne explains the importance of crop rotation in the vegetable garden to feed the soil and avoid disease – and shares her four year rotation plan.

Vegetable garden
Rotate your vegetables to avoid disease and to help feed the soil

Why rotate your crops?

It’s really important when growing vegetables to get a crop that you can use and enjoy, because if it succumbs to disease or gets ravaged by pests it’s a complete waste of time. The best way to avoid both problems is to rotate your crops so that they move round your plot. Then if carrot root flies have infected your carrot crop in one year, they are less likely to suffer in the next year if they’re not growing in a different spot.

Potato blight can also be kept in check by rotation because infected tubers can overwinter and spread the disease much earlier in the year. Always remove self-setters from the previous year. Rotating will also prevent eel worm and scab from becoming a problem.

It’s also important on another level because some crops, such as brassicas, need lots of nitrogen to produce lots of leafy growth. If they’re planted after legumes the soil will be richer due to the nitrogen-fixing root nodules produced by peas and beans. Therefore brassicas should always follow legumes, although you’ll still have to feed your brassicas with a nitrogen-rich feed such as 6X. Apply after planting out in May and then again in August.

Every crop exhausts the soil in different ways so moving them on helps them to find the nutrients they need in fresher soil where other things with different demands have grown.

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A four year rotation plan

A four year rotation works well, so draw up a simple plan depicting your four main areas.

Divide your crops into the following four categories and plant them in this order year by year.

Year 1: potatoes
Year 2: legumes (ie. all peas and beans)
Year 3: brassicas (all cabbages, turnips, swedes and kohl rabi)
Year 4: root crops and onions (parsnips, beetroot, carrots, leeks, shallots, onions, celeriac, fennel)

After harvesting your root crops add manure or compost to enrich the soil before starting the rotation plan from the beginning.

Why this order?

The theory behind this rotation plan is that potatoes exhaust the soil. The legumes, which are planted next, replace nitrogen via their root nodules. Brassicas, which come next, need lots of nitrogen. Root crops do not like to be overfed so they don’t mind poor soil. They develop tap toots or globes to store food. The plot should be manured over winter, or you can dig garden compost in, after the root crops have been lifted.

Visit our fruit and vegetable section for growing guides

Other vegetables

There are crops that don’t fit the main rotation, such as courgettes and squashes and perennial kales etc. These need to be put into gaps as and when.

Sweetcorn and all cucurbits (squashes, courgettes, cucumbers etc) all need good growing conditions so it’s worth adding friable garden compost to a patch of ground during the winter.

Spinach and lettuce can be used as catch crops between rows of carrots etc.

You’ll also get spaces around courgette plants, so make use of all your ground.

You may have to find room for asparagus and rhubarb, which stay put for many years, so five distinct areas may suit some gardeners more than four.

Feeding between rotations

It’s also possible to add nutrients between crops and before crops with specific needs, such as onions, are planted. Stubby-rooted crops such as onions, shallots and garlic can’t send out deep roots to search for food so they need moisture and food in the top couple of inches.

Only add fertilisers during the growing season, because these additions tend to be washed out of the soil during winter and the nitrogen gets into water courses.

Light sandy soils tend to be hungrier. Clay soil is much more fertile, so needs less fertiliser.

Easy to apply fertilisers

Blood, fish and bone
An all-purpose well-balanced plant food for building fertility. Can be used when planting or sprinkled on later. Good for brassicas and easy to handle.

A slow-acting source of phosphorous with nitrogen, best for developing good root systems.

Chicken manure pellets
Nitrogen-rich and easy to apply, although the smell can put gardeners off. Dogs will also consume them. Like all chicken-based fertilisers the smell can attract foxes. Brassicas usually need more nitrogen in the growing season.

Read our guide to understanding different plant fertilisers

Tips for a healthy, disease-free vegetable patch

Make sure that every fourth year the ground is thoroughly enriched with well-rotted organic matter, either animal manure or material from your compost heap. This will improve soil structure and nutrients and your soil will not dry out as readily. Do this after root crops and onions.

Use sprinkle on, easy to apply organic fertilisers and liquid feeds to boost nutrients as appropriate and as recommended by the maker. These boost nutrients for short while, but do not improve soil structure.

Don’t overfeed the soil with nitrogen. You’ll get soft, sappy growth that’s more prone to disease and insect attack.

Remove all self-set potatoes as soon as they appear.

If carrot root fly has become a problem, get your carrots up by January and turn over the ground roughly.

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The opinions expressed are those of the author and are not held by Saga unless specifically stated. The material is for general information only and does not constitute investment, tax, legal, medical or other form of advice. You should not rely on this information to make (or refrain from making) any decisions. Always obtain independent, professional advice for your own particular situation.