Crop rotation reduces the build-up of unwanted pests and diseases in soil, and conserves food reserves so reducing the need for extensive manuring.
Avoiding the cultivation of the same vegetable on the same ground repeatedly, over a period of years, this will slow down, but not prevent, the build-up of soil borne diseases such as club root and white rot, however, airborne pests are less influenced by rotation.
The idea of crop rotation has been taken from farmers, who rotate crops each year, to make the best use of the ground.
Farmers will use root crops 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 to grass.
Such systems of rotation are impracticable on allotments or in small gardens, principally because of their relative size, and the necessity to keep much of the ground in constant use.
A type of rotation that can be followed roughly in most gardens / allotments is to divide the ground into three approximately equal sections, and devote one mainly to root crops such as potatoes, one to green crops such as Brassicas and finally one to peas, beans and other vegetables.
Then in the second year everything can be shifted on one place, the brassicas follow the potatoes, Peas Beans & other vegetables follow the brassicas and the potatoes follow the beans & other crops.
The third year there is a similar shift on, and the fourth year the crops come back to their original plots.
This is known as a three year rotation system.
Some growers will take this a stage further and have a four year rotation, by dividing their plot into four beds.
Three year rotation:
Apply copious amounts of manure or organic matter, and plant potatoes,
Potatoes make high demand on the nitrogen in the soil, and benefit greatly from applications of well-rotted animal manure.
Plant brassicas, including radishes, swedes and turnip, these will thrive on the residue of the previous years heavy manuring.
Green crops do not require as much in the way of manure, their nitrogen needs can be supplemented with the use of a nitrogen fertiliser.
Not manuring, also means that lime can be added, to assist club-root control, which otherwise would have reacted with fresh manure had they been done together.
Plus the fact potatoes prefer a lower soil pH than brassicas.
Plant crops such as: beetroot, carrots, parsnips and onions, peas and beans require very little in the way of humus.
Manure is not suited to beetroot, carrots, and parsnips,as these crops require an abundant amount of potash rather than nitrogen.
Peas and beans, on the other hand may require the soil supplementing with more organic matter.
Year 1: A : B : C
Year 2: C : A : B
Year 3: B : C : A
Year 4: back to A : B : C
The rotation schemes listed above are practical solutions, however, every grower should devise a rotation system that best suits their individual needs.
A fundamental point in any system of garden rotation should be that, so far as is possible, green crops and potatoes should be followed by roots.
Problems you may encounter:
Brassicas generally take up more space than either potatoes or root crops resulting in them encroaching into areas that don’t fit the plan.
Try growing fast growing brassica subjects such as radish and turnip elsewhere, the fallow period created between harvesting and the time the ground is required again, should fit in reasonably well.
Peas and Beans can cope quite well with an abundance of humus in the soil meaning these can be taken out of sequence and moved into Bed A.
The following season’s brassica crop will benefit from such a move providing the nitrogen-fixing roots of the peas / beans are dug in after harvesting.
Personal Computers can simplify the upkeep of rotation records.(see here)