The secret world beneath your garden, with Dr Frank Ashwood

Claire Venice (0:00)

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Claire Venice (0:44)

Hello and welcome to the award-winning BBC Gardeners' World Magazine Podcast, brought to you by the team here at the magazine. Join us as we chat all things gardening with the nation's favorite experts.

We spend so much time thinking about what's growing above ground, but beneath our feet lies an extraordinary hidden world that's absolutely vital to our gardens and to life itself. Hello, I'm Claire Venice from the magazine, and I'm joined by soil ecologist Frank Ashwood to take a closer look at the fascinating life within our soils. From microscopic organisms to earthworms and other creatures quietly working away underground, we'll discover what makes healthy soil such a complex living ecosystem, why it matters to the plants we grow, and the important role it plays in biodiversity and the wider environment. We'll also find out what gardeners can do to protect and nurture this remarkable world, and why understanding what's happening beneath the surface might just change the way we garden. Hello, Frank.

Frank Ashwood (1:47)

Hi, Claire. Thanks for having me.

Claire Venice (1:48)

Well, this is a really fascinating topic, and I'm excited to delve deep to find out more, excuse the pun. We tend to think of soil as simply stuff that our plants grow in, and we know that we need to have healthy soil, but what exactly is soil made of, and just how alive is it?

Frank Ashwood (2:07)

It's a great question. Soil is made of four main things. You've got the mineral component, which is the sand, the silt, and the clay, and that tends to make up about 45% of soil.

You've got air and water, which each roughly make up about 25%, and then the rest, that last 5% is the bit I'm really interested in, is the organic matter and the life. So that's all of the decaying plant material and decaying animals, but it's also the living animals as well. So about 5% of the soil is alive or sort of decomposing organic matter.

Claire Venice (2:39)

Interesting stuff. So where did your interest in soil begin?

Frank Ashwood (2:42)

Well, I actually have my mother to thank for this. So some of my earliest memories are her taking me to the back of the garden and showing me all of the life that was under the rocks and the logs that we had sort of piled up there. And I didn't realize it at the time, but it was probably leaving quite a deep impression on me because I somehow eventually found my way to becoming a soil ecologist later in life, of all things, which isn't something you necessarily accidentally fall into, I guess. But no, who knows.

Claire Venice (3:06)

What did you think you were going to become when you were young?

Frank Ashwood (3:08)

Well, I didn't aspire to do a PhD in earthworms, I have to say, but I'm glad that I did.

Claire Venice (3:15)

Well, I mean, that's interesting in itself.

I think worms are the first sort of indicators, or the first kind of introduction we have to soil as gardeners. We hopefully see a lot of them in our soil. That's an indicator that the soil is healthy. But there is far more to the soil than just earthworms. Can you explain a little bit more about what else we can find there?

Frank Ashwood (3:33)

There is. Well, so soil is actually the biggest reserve of biodiversity on the planet. It's been estimated recently that about 59% of all of the world's biodiversity is in the soil. So that's plants, invertebrates, mammals, some mammals like moles and rabbits and that kind of thing. And so soil has a huge amount of life in it, beyond just earthworms. Although in the UK, we have about 31, 32 species of earthworm, which not a lot of people know.

So, you know, we should be proud of our earthworm biodiversity in the UK as well. But yes, so soil is alive, basically. The thing that gives soil its characteristics is the life in the soil and the interactions between the life in the soil. So, if you dig down into your garden and into your soil, and you go looking for life, you might need a little hand lens or something to see some of it because it's very small. But it's absolutely teeming with life. You know, in a square meter of your garden, if you would somehow excavate like a cubic meter of that soil, you could find maybe 100, 200 earthworms if it was healthy. You could find maybe 50,000 tiny little invertebrates called springtails. You could find 100,000 mites. You could find 5 million nematode worms, which are microscopic little worms that live in the soil.