A lecturer in horticulture and author says that the amount of organic matter in soils effects their smell, and how good that smell makes us feel.

Julie Kilpatrick is sniffing soils as part of the research for her new book 'The Plant City'.

She says: “Soils rich in organic matter smell sweet and pleasant, while depleted soils don’t smell much at all. That’s because bacteria in soils survive by feeding on organic matter and some of them produce a substance responsible for that sweet smell, known as geosmin. If you can smell geosmin, you know you have a soil that is healthy and full of microscopic life and, very likely, the bacteria which makes us feel good will be part of all that life.

"Even if you don’t have a garden, all you need to do is to get outdoors and inhale healthy soil. One of the best places to find soils rich in organic matter is in wooded areas where the plants look after the soil and there’s little interference from humans”.

Julie says the smell of geosmin is at it's most noticeable when it rains after a dry spell. Apparently that sweet smell of summer rain has been given a name – petrichor – and it’s a mixture of geosmin disturbed by raindrops and oils exuded by plants during dry spells. Julie thinks its nature’s way of telling us it’s happy the drought is over.

She says: “I don’t know anyone who doesn’t love that smell and the pleasure it gives us is so primitive. Our ancestors, who depended solely on soils for their survival, would have felt a tremendous sense of relief upon smelling petrichor and we have retained that feeling, even if we don’t quite know why.

"Gardening has always been considered great therapy but now we know you don’t have to be a gardener to benefit. Just get yourself out there and feel the living, breathing, medicinal earth beneath your feet and, while you’re out there, pick up some soil and give it a sniff.”