Science Interviews

Interview

Sun, 15th Jan 2006

The Science Behind Composting

Dr Tim Upson, Superintendent of Cambridge University Botanic Gardens

Part of the show Plant Science, Composting and Mosquito Repellents

Tim - Composting is perfectly natural process. It's the process by which any organic matter decays and basically composting in gardens, for example, creates a very useful substance which we usually use to enrich our soil.

Chris - What actually does the composting process? Presumably it's some sort of thin gin the microbiological world.

Tim - That's correct. It's things like bacteria that are the primary decomposers. Then as the compost matures, other organisms such as fungi and particularly worms, woodlice and even slugs in very mature heaps come in a really refine it. If you get those organisms coming in you produce this really fine substance that's really nice to handle and to use in the garden. Of course, plants love it and it promotes plant growth and produces very healthy soil. This is all necessary whether you're growing ornamental plants or vegetables in your garden.

Chris - What are the best things to sling on a compost heap, and are there any definite no-nos?

Tim - Yes, I suppose it's a little bit like cooking to a degree. What you want to do to create an ideal mixture is to include greens. These are things like lawn clippings, annual weeds and anything which is green and breaks down easily. This needs to be mixed in with something called the browns. These would be things like twiggy branches, all the way through to household products like toilet roll holders. That adds bulk, keeps the compost open, and allows the air to penetrate. All of the bacteria and worms can keep functioning properly because they have a good air supply.

Chris - Dot he worms actually make much of a contribution, because presumably if you do get worms flocking to your compost heap, they mix things up and down. Do they do anything else?

Tim - Yes, worms are the gardener's best friend in many ways and of course they naturally occur in the soil. If you've got your compost heap directly on the soil then they will penetrate into it.

Chris - What about adding worms? If you buy in worms, is it useful?

Tim - Yes, you can do that. In fact there are now systems available which take advantage of the fact that worms eat organic matter. It passes through their gut and comes out the other end as worm poo and that produces something called worm compost. It's actually very rich, and usually it's diluted down by mixing with a normal potting compost from a garden centre or some other compost from heap. If you use it on its own, it's too rich, but it's a wonderful substance and if you use it in the right way, it can really promote growth. In the botanic garden we have a display showing a whole range of different composting options. Some require lots of space but I always feel that one of these little worm bins, even if you live in a flat that maybe has a balcony, you can put it out there and keep it going with kitchen waste rather than putting it into the usual landfill stream.

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