Organic Soil Improvement and Companion Planting
Special cultural practices play an important role in organic gardening. Mulching the soil not only improves it and keeps it moist in summer, but also keeps weeds under control. But weeds are not always enemies — some provide food for the adult stages of insects whose larvae are predators on other insects, and a light cover of annual weeds will keep the soil cool and moist in summer. Provided the weeds are removed before they set seed, they will do no great harm. Exceptions are groundsel and chickweed which should be pulled up while quite young as they can harbour cucumber mosiac virus which has a wide host range and can be very destructive.
If there is space in the vegetable or fruit garden, a good way of improving the soil is to grow a ‘green manure’ crop such as mustard or winter tares and dig it in before it flowers. This will build up the humus content in the soil as organic manures do.
Rotation of vegetable crops does much to prevent the build-up of pests and diseases in the soil that results from growing crops in the same soil every year.
Pests and diseases can be avoided by growing plant varieties which are known to be resistant — some modern fruit and vegetable varieties are bred especially for this quality. There are rose varieties which are resistant to black spot and/or mildew, varieties of apple which defeat apple scab disease, and so on.
One of the best ways of preventing epidemics of pests and diseases is to grow mixtures of plants, rather than blocks of one kind — a mixed herbaceous border, for instance, will be more trouble-free than a formal bedding scheme with lots of the same species blocked together. Similarly, roses mixed with shrubs or herbaceous perennials will be less likely to be plagued by greenfly. Mixing rows of vegetables is another method, such as lettuce between sweetcorn.
The theory of true companion planting goes further still — certain plants grown close together actually benefit one another, and other plants can have bad effects. Chives are claimed to control black spot disease on roses, carrots mixed with onions ward off carrot fly, and hyssop attracts cabbage butterflies away from cabbages. Gladioli, on the other hand, can inhibit the growth of nearby peas and beans, and fennel has a bad effect on tomatoes.
Falling back on inorganics
The gardener can plump for a strong decision one way or the other – to use solely organic principles, or to use inorganic methods wherever appropriate. The latter approach will probably appeal to the majority of people and there are, indeed, times when inorganic gardening is helpful and occasionally necessary. On an old, played-out site where the soil is little more than stones, sand and rubbish, quick-acting mineral fertilizers must be used at least for the first few years.
Occasionally, in spite of all one’s efforts, epidemics of pests or disease do occur. The best way to deal with such problems is to apply a quick and thorough blanket spray, preferably using one of the insecticides or fungicides harmless to the ‘goodies’. The aphicide pirimicarb, for instance, is specific to aphids and will not harm any other insects, including pollinating bees.
Among the choice of pesticides, many are quite harmless to humans and animals — in particular, the synthetic pyrethroid group of chemicals, for example permethrin, similar to the pyrethrum obtained from plants, but even safer and more effective.