‘I love compost like one loves a woman’.

Not my words but those of Octave Mirbeau, a 19th century anarchist, writer and keen gardener.

I am a gardener myself, though not a particularly successful one, and though keen on compost I cannot say I’ve ever seen it in a sexual light.

It’s true a well rotted compost has a sweet smell, a fine structure and should be treated as a living thing.

In fact it’s packed with so many organisms it’s a wonder it doesn’t get up and wander away.

Added to garden soil it not only supplies nutrients and improves the tilth but injects a new vitality.

It is precisely the problem of modern agriculture that it has treated the soil as a plant laboratory, seeking ever more sterile conditions, leading to a national decline in soil fertility.

As a columnist writing on urban wildlife I haven’t often turned to soil microbes are a subject but if the criteria were based on quantity alone they would certainly merit a mention.

A single tablespoonful of healthy soil contains more microbes than there are people on earth. The same tablespoon would also contain species of nematode, or roundworm, that are completely new to science.

It is not surprising that after 6,000 years of tilling the soil, and several million more of living in close proximity with it, we have formed a symbiotic relationship with many of these living constituents.

Some species have entered the human gut; either through accidental ingestion, pores or skin cuts. They have set up home, taking advantage of a protected environment and guaranteed source of nutrition, in return bestowing benefits on the functioning of the body.

The human being is not a discrete single entity but a multitude of organisms working in concert.

One of these organisms that has been subject to study is the soil bacteria Mycobacterium vaccae whose name derives from vacca, the Latin for cow because it was first artificially cultured on cow dung.

Despite this unpromising origin, research has suggested that its presence in the body helps counteract a list of conditions including asthma, cancer, leprosy, psoriasis, dermatitis, eczema and TB. Most interestingly, it promotes the production of serotonin so is an antidote to depression.

It is claimed the uplifting effects of more M.vaccae entering the body, say from a hands-on gardening session, can last up to three weeks. Horticultural therapists have long argued that gardening was good for mental health; through physical activity, being outdoors and contact with nature.

But this is the first evidence that benefits come from literally getting your hands dirty. Recent research was carried out at the University of Bristol where the bacterium was injected into mice. Their anxiety levels were then tested including placing the mice in tiny swimming pools.

I cannot rid myself of a mental impression of the untreated mice thrashing about in panic while the injected ones lie on their backs on lilos and gently paddle over to the cocktail bar.

Our avoidance of dirt and decreasing contact with soil and its living organisms could be counter-productive - a factor in the growth of modern allergies and conditions.

Personally, I am determined to get into the garden more. It’s so much better than a gym work-out and a whole lot cheaper than therapy. I may lack the same feelings for the compost heap as Monsieur Mirbeau, but a bit of dirt under the fingernails is surely a real pleasure.