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Allotment Guide

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Veg intro (Part 3)

Sowing Planting Harvest Guide

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Runner Beans


Allotment Plot Holders' Guide:
Principles of Vegetable Growing (part 1)
Vegetable groups and crop rotation

With the large range of vegetables now available from supermarkets or greengrocers, most of which is of high quality, it could be expected that production of vegetables on the allotment might be in danger of dying out. However, this does not seem to be the case and some of the reasons may be:

Vegetable Groups

It is convenient to group vegetables into broad categories because some are closely related and have similar cultivation requirements, which are different from other groups.

We can identify five groups:

  1. Permanent plants Most vegetables are grown as annual plants. That is, we plant and harvest them within one year. There are however, some that are perennial, such as rhubarb, artichokes and asparagus. These plants need to be assigned a permanent position on your allotment plot.
  2. Brassicas Brassicas come from the genus Brassica and include cabbage, cauliflower, broccoli, brussel sprouts, Swedes and turnips.
  3. Legumes Legumes come from the family Leguminosae and include beans and peas. Legume actually means a pod and a characteristic of the family is that the seeds are contained in a pod, which is the fruit. Another characteristic of legumes is that they have a symbiotic relationship with the bacteria rhizobium, which results in nitrogen being fixed in nodules on the roots of the plants.
  4. Alliums Alliums are bulbs and come from the family Alliacaea and include onions, leaks, garlic and shallots.
  5. Root Crops This group includes those plants with swollen taproots, such as beetroot, carrots and parsnips.

There are some vegetables that do not fit into the above categories and will be covered separately. These are potatoes, which are stem tubers, and salad crops like lettuce, tomato and cucumber.

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Principles of Crop Rotation

One reason for dividing the vegetables into groups is because it is beneficial to grow the groups on different pieces of land each year. This process is called crop rotation and is usually done on a three or four year cycle. The longer the cycle the better.

The reasons for crop rotation are:

  1. To minimise plant problems. If crops are grown in the same area each year this can lead to a build up in the soil of harmful pests and diseases and to a depletion of the nutrients required by the crop. This is given the general name of ‘soil sickness’ and it can cause the yield from the crop to deteriorate.
  2. One crop can benefit from the previous one. Legumes fix nitrogen in the soil, which can then be utilised by brassicas, which require a good supply of nitrogen. Potatoes help to suppress weeds because of their dense foliage, which can then be followed by alliums, which are poor weed suppressers.

A Traditional Three Year Cycle

  Year 1 Year 2 Year 3
Bed 1 Brassicas Roots Legumes
Bed 2 Roots Legumes Brassicas
Bed 3 Legumes Brassicas Roots

Alliums and salad crops should be included with the legumes. Potatoes require soil rich in nitrogen and benefit from being grown after the legumes. Do not grow potatoes in with brassicas as the lime applied to control club root may well induce potato scab.

Treating alliums or potatoes as a separate group could create a four-year-cycle. When we discuss ground preparation, we will see that the preparation for each group is different.

Limitations of Crop Rotation

In a commercial situation, and particularly in agriculture, there is no doubt that crop rotation is important. However, in an allotment plot it must be said that it is not always easy since the personal preference of the grower will dictate what they grow, which could be all of one group. Also, the argument about pests and diseases is not so relevant since they are mobile over a small area and some can survive years in the soil.

In these circumstances more practical advice would be:

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