Make your own compost hot mix, step-by-step (part two of three)

Compost part one, saw us looking at low tech, low input ways of dealing with green waste. Here we look at how to make hot compost which sterilises the mix.

1) Compost needs five ingredients:
a) nitrogen
b) carbon
c) oxygen
d) water
e) microbes.
You need to actively manage the process with a hot compost mix. The common failing of the black plastic drum as a compost bin is the lack of carbon and the lack of oxygen which means you get a soggy, sludgy mess. Carbon comes from dry, woody material – twigs (cut up small), newspaper (needs to be shredded or scrunched up), wood chips, sawdust (not tanalised), wood ash, dried leaves. As we make a lot of compost, we get much of our carbon content from the mulcher or wood chipper. Carbon content should comprise close to half the total volume of your compost and, as it is often bulkier, it creates air spaces in the mix.

2) The other half, or a little more than half, of your compost ingredients comes from the green waste (which is the nitrogen component). This includes all green leafy waste, animal manure, food scraps and lawn clippings. Compost microbes will come in with the grass clippings, or you can add some of your old compost mix (the old twiggy bits can go through again).

3) We simply pile it all in a heap until we get enough to work with. Wooden compost bins are a tidy option for the small garden. You need three – the first to accumulate the waste, the second to make it in and the third for compost which is ready to use. Make sure that you can remove all the boards from at least one side to make it easy to move the compost through the bin cycle. Each bin needs to be around a cubic metre at the least. A ring of chicken netting is the low tech method of keeping your growing compost pile contained and is probably easier to work with though less tidy.

4) When you have sufficient volume to work with, adding nitrogen in the form of fresh grass clippings, fresh animal manure, urea or blood and bone will give your compost a kick start to generate heat. Mix it all up. When done by hand, the garden fork is the usual tool to mix. We do the mixing with a baby tractor which is admittedly easier but a little excessive for small town gardens. Cover the heap from here on.

5) The heat should reach between 55 and 75 degrees Celsius within a few days. Turn the heap again – sides to middle – to get the whole lot working. You can see the clouds of steam pouring out of our heap which indicates heat. There will be no worms or insect life in hot compost mix. The heat should also kill off weed seeds and undesirable pathogens. Ideally, turn a third time a few weeks later.

6) Cover and leave the compost to cure for a couple of months or longer. The compost will now cool down and it should be light, friable (almost fluffy), clean and have no offensive odour. In our high rainfall climate, we recommend covering with something reasonably waterproof to prevent the goodness from being leached out. We use old weed mat weighted down at the base. You can also use heavy duty black polythene. Boards or corrugated iron are common on a tidy compost bin structure.

Part three – making cold compost mix.