Plants are only as healthy as the soil they grow in and soil is only as healthy as the life within it. The largest and most important players in this drama are earthworms, of which there are some 3,000 species, including an Australian one that grows to a length of three metres. The 25 British species can be divided into three groups.

Gardeners are probably most familiar with epigeic or compost worms, which are recognisable by a red stripe along their backs. Living on the surface and feeding on leaf litter and other decaying vegetation, they’re attracted to the mountains of goodies in compost heaps and readily take up residence.

The second – anecic – group contains most of the UK’s worm species. They have dark red or brown heads and the body turns pale towards the tail. Like compost worms, they help process rotting vegetation. They specialise in creating permanent vertical burrows which they use to transport fragments of vegetation throughout the soil.

Endogeic species, the third group, are responsible for processing soil. They make horizontal burrows through the ground and sometimes move backwards and forwards along their tunnels. These worms ingest microbes in the soil, bacteria, protozoa and fungi, which they digest and excrete as wormcast.

This wormcast is much more nutritious than the original soil. Although it’s almost impossible to assess exactly how nutritious it is, it has been estimated wormcast could be as much as 59 per cent richer than the original soil. It certainly has a higher NPK (nitrogen, phosphorus and potassium) value and contains minerals such as calcium, copper and zinc. Other soil microbes continue the process of breaking down this fertile material and making it available to plants. Gardeners know the compost from their wormeries is the richest kind of compost they can make at home, so “wild” wormcast must be up there too.

The soil food web and the part played by all this life is terrifically complicated; to put it simply, however, the more organic material in the ground, the larger the community of worms and microbes you’ll have. All this activity will lead to richer, more plant-friendly soil.

If you use synthetic chemicals in your garden you’ll disrupt this natural ecosystem and impoverish the soil. The normal reaction is to use more synthetic fertiliser which, in turn, causes further degradation.

Advocates of synthetic fertilisers are right when they claim a plant gets all the food it needs from these chemicals. But, without organic feed, their soil will be lifeless or nearly so. There will be very few bacteria to bind soil particles together, which makes it crumbly, able to retain moisture and hold the wealth of air pockets that plant roots need. With so few microbes, there will be less food for worms and therefore fewer of them. Like an addict, this ground will keep on needing its chemical fix.

You’d expect an organic gardener, like me, to bang on this way, but there is plenty good scientific research data to support my views. Several papers have addressed the subject over the past few years. In one, published in 2014, the University of South Denmark’s Claudia Wiegand and Francoise Binet of the University of Rennes outlined the results of their assessment of the effect of fungicide on worm populations.

The scientists reported: "Worms have developed methods to detoxify themselves, so that they can live in soil sprayed with fungicide." The fact the worms used their energies to survive in these conditions meant they became smaller than usual. There could be up to three times as many worms in uncontaminated soil. Wiegand and Binet concluded: "An explanation could be that they are less successful at reproducing, because they spend their energy on ridding themselves of the pesticide."

So if you want a healthy worm population, don’t use synthetic chemicals on your soil, on the lawn or on paths.