Rotational Cropping has been taken over from farmers, who employ a definite rotation of crops from one year to the next with the object of making the very best use of the ground. Root crops may be used to clean newly broken ground prior to the cultivation of cereals, after which the land is allowed to lie fallow for a year or is put down once more to grass. No such clearly defined annual system of rotation is practicable on the allotment or in small gardens, partly because it is necessary to keep much of the ground in constant use, and partly because of the difficulty of devising any rotation which will give an ideal sequence of crops together with a sensible division of the ground according to the requirements of the consumer.
One advantage of rotation is that it conserves the food reserves of the soil and so reduces the need for manuring. Green crops and potatoes make a comparatively high demand on the nitrogen in the soil, and both benefit greatly from applications of well-rotted animal manure. Such manure is harmful to carrots, parsnips, and beetroots, which require abundant potash rather than nitrogen. A fundamental point in any system of garden rotation should be that, so far as possible; green crops and potatoes should be followed by roots.
A type of rotation that can be followed roughly in most gardens is to divide the ground into three approximately equal sections and devote one mainly to green crops, one to potatoes, and one to roots, peas, and beans and other vegetables. Then in the second year everything can be shifted on one place, the greens coming to the potato plot, the potatoes going on to the ground cleared of roots, and the roots occupying the plot cleared of greens. The third year there is a similar shift on, and the fourth year the crops come back to their original plots. Onions may well stand outside such a system of rotation and have a more or less permanent bed to themselves.
Suggested Three-year Rotation
Cabbages, cauliflowers, brussels sprouts, kale, savoys, and other brassicas. Preceded by, or inter-cropped with lettuces, radishes, and other small salads.
Plot dressed with animal manure or compost and limed (not together). Crops fed while in growth with nitrate of soda or sulphate of ammonia.
Potatoes. Followed by broccoli, spring cabbage, coleworts, leeks, and late-sown turnip (for tops).
Plot dressed with animal manure or compost, but not lime.
Complete artificial fertilizer applied just prior to planting potatoes.
Carrots, parsnips, turnips, and beetroots.
Peas and beans with summer spinach and lettuces between.
No animal manure or compost except for pea and bean trenches. Wood ashes forked in. Complete fertilizer (low nitrogen ratio) applied just prior to sowing.
Plot dressed with animal manure or compost and wood ashes. Nitrate of soda after thinning.
The scheme is applicable to plots of any size or shape, so no dimensions are necessary. The only essential is that sections A, B, and C should be of approximately the same area. They need not be of the same shape. The second year the order of the crops from top to bottom is C, A, B, D; the third year B, C, A, D; the fourth year the same as the first year. Onions are not included in the rotation because they appear to derive greater benefit from being grown on the same plot for a number of years, If, however, it is preferred to include them they should go to plot C.
Intercropping. Some crops take up a good deal of space without anything like occupying all the ground with their roots. Examples are the taller varieties of peas and runner beans. Space is necessary with these to prevent one row from shading the next so heavily that the plants would fall into ill health. But some crops appreciate shade, and it is an obvious deduction to plant these between tall subjects that require a lot of room. That is the simplest form of inter-cropping. Cleverly practised, it can be a great space saver in the garden.
Winter greens or other plants raised in a reserve bed may be ready for planting out before any ground is vacant for them, though a crop is nearing maturity and will shortly be harvested. Under such circumstances it is in order to plant the new crop between the old. Do not intercrop in this way too long in advance of the time of harvesting the preceding crop or the result may be starved and drawn plants.
Catch Cropping. Sometimes ground has to be prepared some considerable time before it will be needed, and it may be possible to get a quick-growing crop off if before that for which it was actually intended is ready to go in. This is known as catch cropping, and is a method of economizing both space and time in the vegetable garden. Lettuces, radishes, spring onions (for use in salads), summer spinach, mustard and cress are a few of the best catch crops, and they may be sown in celery trenches or on the ridges on each side of such trenches, on the ground prepared for the later kinds of winter greens or for very late sowings of quick-maturing peas and in other similar places.
Successional Sowing. If all the seeds of such things as lettuces, radishes, spinach, early carrots, early turnips, or peas are put in at one time the result will be a glut of these vegetables for a few weeks followed by a complete lack of supplies. The right course is to make a number of small sowings at intervals of a fortnight or three weeks so that as fast as one lot is used up another is just coming to maturity.
There are early, mid-season, and late varieties of many vegetables. One important difference in these is in the time they take to reach maturity. For example, an early pea may be ready for picking twelve weeks after sowing, whereas a mid-season variety sown at the same time will not be ready for a further fortnight, and a late kind may take a full sixteen weeks. By a wise selection of these different kinds it will also be possible to lengthen the season and maintain continuity of supply.
For very late sowings an early variety is often selected. This apparent paradox is explained by the fact that there is such a limited period of good weather left for growth that only a naturally quick-growing variety can mature in the available time. This is particularly noticeable with peas, carrots, and turnips.