Next to the peat issue, chemicals are probably the most emotive topic on the gardening front at the present time.
Garden chemicals are basically either organic (derived from natural sources) or inorganic, though some compound fertilizers and insecticide mixtures can be a combination of both.
Those gardeners who prefer only to use chemicals of natural origin often shun those from any other source. It is quite possible to control most common pests and diseases using organic chemicals alone, and it is not necessary to use artificial fertilizers to produce bountiful crops. However, the mistake is often made that all organic chemicals are empathetic to the environment and non-injurious to an eco-structure, whereas all artificial ones are harmful. For instance, one of the most efficient insecticides is derived from the pyrethrum plant, yet its range is so wide that it can wipe out many beneficial insects along with the ‘nasties’ causing the problem. On the other hand, pirimicarb, a man-made product, is specific to aphids and will leave other insects untouched. It is possible to make up a whole range of home-grown ‘brews’ to wage war on the little beasties which deface your plants, and yet, because concentrations of chemicals in them tend to vary, none of them is theoretically as safe, or as regularly efficient, as those manufactured under strict laboratory conditions and quality control. And whether a fertilizer is derived from organic or inorganic materials, it is still capable of being over-applied, causing it to build up in the soil to undesirable levels, or seep away into adjacent watercourses.
In an ideal world, where all plants and animals were in perfect balance, there would be no need for supplementary treatments of any sort. Pests would have their own predators, and even diseases would have sufficient parasitic controls to keep them in check. The Nitrogen Cycle would work efficiently, those plants and animals removing nutrients from the planet in order to live returning the same elements to the earth on death.
However, this system has never worked particularly eff-ciendy, even before the world became overpopulated, resulting in plagues and pestilences. Over the long term, everything would either return to normal or evolve accordingly, but we are here now, we do not generally see things in the long term, and to augment our synthetic lifestyle, it becomes necessary to take action against the things that pose a threat.
When it comes to pest — and even, to some extent, disease — control, probably the most efficient and ecologically sound method is to use artificial barriers. Cabbage root fly can be prevented by putting a collar of old carpet or similar on the soil around the stem at planting time, for example, but better still is to cover whole areas to be kept free from pests with crop-protection sheeting. Growing fruit in a cage will also do away with the need for spraying, but even this method of defence has its disadvantages, the main one being that in excluding the plants from harmful insects you also exclude beneficial ones and wildlife as well, so those pests which are impossible to keep out, such as slugs and snails, are able to run rife. And in an ornamental situation, there is little point in having a pretty border if it is covered up so you cannot see it.
To be truly ‘environmentally friendly’ really requires a change of attitude in gardening. In the flower garden, we should not be so worried about the odd blemish, but work at the overall effect rather than the detail. Most pests and diseases are temporary anyway, and disappear after a time. If they do not, then maybe we should examine whether in fact they have a place in the modern garden anyway. New plant varieties are being bred all the time, which eventually should cut down the necessity for controls of this kind. Do not worry too much if your vegetable and fruit crops do not look like those on the supermarket shelves — it will have taken a lot of chemicals to get them looking like that. The domestic garden of the future should be one where people, wildlife and plants can exist side by side to the detriment of nothing or nobody. In the meantime, help in moderation and with caution may be necessary.