Plant ecologist Ken Thompson offers a no-nonsense approach to home composting. Illustration Jill Calder
Ever since I acquired my first garden – and that’s quite a long time ago now – I’ve made compost. I don’t recall that ever being
a conscious decision; it was just something gardeners did. I’m sure my first compost bin, made from the remains of a Second World War Anderson air-raid shelter, was the only one of its kind, and probably still is.
So you can imagine my surprise on reading the results of a 2022 RHS survey, conducted as part of the organisation’s Planet Friendly Gardening Campaign to promote a more sustainable approach to gardening, which revealed that only a third of gardeners compost their garden waste. I don’t know what’s preventing the other two-thirds from joining in, but I suspect it’s at least partly a perception that it’s difficult, complicated or hard work. In fact, it’s none of those things, as we shall see.
How to make compost
You don’t have to turn your compost heap
Advice on making compost is everywhere, and practically all of it says your heap needs turning; in fact, possibly turning quite often. It does not. In more than 40 years of compost making, I have not once turned a compost heap, nor have I felt the slightest urge to do so. A reason for turning is rarely offered, but when it is, it’s usually something about needing to add air. Which is fair enough,
as composting does indeed need air.
But if your compost heap is airless, slimy and evil-smelling, that’s usually because you added a mountain of grass clippings all in one go. Make sure you add a reasonable proportion of carbon-rich ‘brown’ material with the green stuff, and all will be well. If your garden is short of the right kind of stuff, add scrunched-up cardboard, such as egg and cereal boxes. The compost heap is
also the safest place for all your old bank statements and credit card bills.
Your compost heap might not get hot
Something else all the official advice says is that your heap will get hot. It may not, or at least it may do so only briefly, and this may make you think you’ve somehow gone wrong. The reason for the failure of a typical-sized, home compost heap to get hot is simple: its surface area-to-volume ratio is too big to prevent heat escaping faster than it is produced. If you want it to stay hot, you’ll have to significantly increase the size of your compost heap or insulate it well. But don’t worry too much; the bugs that compost waste work perfectly well at ambient temperature.
You can buy insulated ‘hotbins’ that will get properly hot, but I’m not sure the expense is worth it. A hot bin gives you the illusion that things are happening faster, but they’re not; ultimately the rate at which you can make compost depends on the rate at which your garden supplies the green waste, not on the rate at which that waste turns into compost. Thinking otherwise is like imagining that you will be better off if you spend your money faster – but your spending power depends on your income, not on how fast you spend it.
The only real advantage of a hot heap is that it will kill the seeds, roots and rhizomes of weeds. But the best defence against weed seeds is vigilance, so that weeds end up on the compost heap before they get round to setting seed.
Deal with roots or rhizomes of perennial weeds, such as dandelions, docks and couch grass, by killing them before they go in the heap. The easiest way to do that is to leave them somewhere dry and sunny until completely shrivelled, although a more satisfying solution is to bash them thoroughly with a hammer.
The basics of a compost heap
The starting point of your compost is a pile of green waste, and the end is just a lot of water and CO₂; if you left your heap long enough, it would eventually just disappear. Somewhere along that journey your compost is ‘done’, but there’s no way I can tell you when that point is – that’s up to you.
If you’re worried about what your compost looks like, perhaps impressed by TV gardeners caressing handfuls of lovely, crumbly material from their own heap, you will wait longer. If you’re less bothered about aesthetics, you’ll be content with a younger, lumpier and more heterogeneous product. But there are no prizes for what your compost looks like, and both will work just as well. One thing to remember is that the more you chop up tough stuff into small pieces, the sooner your compost will look like the finished article. You can add a moderate proportion of relatively rapidly decomposing tree leaves, such as ash, cherry, lime or willow to your heap, but either quarantine tough leaves, such as oak, beech and chestnut, in their own heap, or let the council look after them.
But whatever your compost looks like, don’t even think about digging it in. Just spread it on the soil and let the worms do the work.
Do you need a compost bin?
Strictly speaking, you don’t need a bin at all to make compost. But most of us use one, if only for the sake of tidiness, and I think the most convenient type is one of those conical, recycled plastic ‘daleks’. It may have a hatch at the base, but there’s no need to bother with that. When the time comes, just lift the whole bin off to get at the finished compost. A pragmatic approach is to have two bins, one maturing while the other is being filled up. When the second bin is full, the compost in the first one is done – by definition. …
How to compost: the basics
So, in case you missed it, here’s my foolproof compost protocol:
1. Fill first bin.
2. Fill second bin.
3. Spread contents of first bin on garden.
If only all gardening were so simple.