Most things die down at the end of the growing season, but one that definitely gets bigger is the compost heap. What with spent crops from the veg plot and waste generated from preserving the harvest, there’s plenty to add to it.
Which is when the anxiety starts. As a member of my local composting group (something at which my friends have finally stopped rolling their eyes!) I give out advice to the compost-challenged. An awful lot of people find composting difficult – not surprising, given that some instructions sound like a cake recipe. But, unlike a cake, a poorly performing compost heap can always be rescued.
Let’s admit it: no one gets it right all the time. I opened a bin recently to find a busy ant colony (watering dispersed it – ants move in when the heap is too dry). A friend’s heap smelt of ammonia – he’d known that he was adding too much fruit waste but had done it anyway (that sounds familiar!). It was easily sorted by mixing in drier stuff to break up the wet, compacted material (which rots, rather than composts, and produces that pungent stench).
Before you think your heap’s not working, it’s worth remembering that composting isn’t fast. Made at the end of the growing season and left to its own devices, a heap is likely to produce usable compost, at least in part, in time for next summer. But it could take longer, depending on how fine a compost you want, what’s in the heap, even the weather. And there’s nothing wrong with that. Honest, usable compost in over a year is not a failure. Not if you like to take things easy.
Basic Composting Needs
However, for those of us who fidget (OK, that’s me), compost is achievable in a much shorter time. You need to keep an eye on a heap’s basic needs: warmth, moisture, air, carbon and nitrogen. And you’ll need to turn the heap. If you’ve got a bad back, this probably isn’t for you.
So, warmth. Ensure that your heap or bin measures at least 3’ x 3’ x 3’ (1m³), preferably more. Those dinky little bins shaped like beehives? Ignore them. A bigger volume of material gives the bacteria more to work on, so it heats up more easily and stays hot longer. And moisture is easy too. Your bin’s contents should be as wet as a squeezed-out sponge. Water if necessary and protect from the rain to prevent excess sogginess. As far as air is concerned, you can tell from the "leave it" method above, enough will penetrate to create compost. But nothing speeds up a heap like turning its contents, introducing oxygen back into the centre, firing up the bacteria. With these three elements looked after, your heap should be breaking down all that nitrogen and carbon as fast as its bacteria can say "aerobic respiration".
The carbon and nitrogen demands cause the most worry. Best described as "browns" and "greens", carbonaceous (brown) material is dry, dead matter, such as old stalks, egg boxes, twigs, sawdust; nitrogenous (green) material is sappy and damp, such as grass cuttings, vegetable peelings, rotting fruit. Mixing these in approximately equal amounts is easiest, though up to a ratio of 1:2 is usually OK.
Whatever you add, make sure that it’s well chopped up. Chunky material like broccoli stalks should be crushed (now’s the time to indulge in some good hammer-thumping therapy) or well chopped with a spade. This opens up the insides, allowing bacteria to get to work faster. Mature prunings are best put through a shredder, though cutting them up small with pruners is better than nothing. You want small pieces that mix together easily, so the browns and greens are well distributed and not all in one lump.
What Not to Add to Compost Heaps
In theory, a heap like this heats up sufficiently (to 140°F for several days) to kill off weed seeds and plant pathogens. But really, I wouldn’t risk it. You just can’t guarantee that every part of your heap gets hot enough for long enough, even with several turnings. So, diseased and invasive plants are best burnt or thrown out. Brassicas with club root, onions with white rot, mildewed leaves – all out. Blighted tomatoes are contentious – now an airborne fungus, blight is, some argue, fine to put in the heap. But again, I wouldn’t risk it. Composting perennial nasties like bindweed, mare’s tail and ground elder just isn’t worth the danger of spreading them round the garden.
Otherwise, it’s up to you what you’ll tolerate. Every year, tomato seedlings spring up like weeds in my beds, but it doesn’t bother me. Some I let grow; others feed the compost bin. If you don’t want self-sown plants, ensure that seed heads are removed before you add plants to your heap.
Helen Gazeley is a UK garden expert who writes for Kitchen Garden Magazine and her own blog Weeding the Web