Most people take soil for granted, assuming that if you shove a seed into some dirt and add some water, hey presto. Stick it under an electron microscope, however, and you suddenly see a whole microcosm that exists beneath our feet. Landscape gardener Chris Beardshaw takes us on a tour to see why soil is so important, what risks it faces and what happens to it when we're not paying attention. It may not seem like the most entertaining subject for a TV documentary, but there's plenty of useful facts about dirt that you'll be able to wheel out the next time you go for a walk. Unless you're a germophobe, of course.

Deep Down and Dirty, The Science of Soil is available to stream on BBC iPlayer.