Behind the scenes in Compost World

Composting is a lovely blend of art and science, exactly the kind of natural mystery that appeals to the amateur scientist lurking within me. I'm getting better at it after several years of mixed results, but it's certainly not as easy as it seems. As I've just spent a few hours this cool morning spreading around my latest batch of compost, and it's probably my best so far, I thought I'd talk nothing but rot today.

At my place, Compost World is hidden by this simple little hedge of two Murraya paniculata plants. Murraya is a wonderfully easy-care hedging plant with fragrant white flowers, and it's also a good nesting site for small birds such as bulbuls, which build a nest there every year.

And here's a peek behind the hedge. It's where the compost bins live, along with the spare pots and a small assortment of ferns, all under the shade of an olive tree and Pam's office/shed.

And here's this morning's harvest of compost from the big tumbler bin. This batch is probably the best ever – dark, crumbly and sweet smelling.

This tumbler bin isn't perfect, but it's the best choice for my garden. It scores 10 out of 10 for aerating the compost, but its one drawback is that its contents never get hot enough to kill off seeds from vegie scraps such as tomatoes, cucumbers, pumpkins and capsicums. I just try to keep as many seeds out of the compost as possible in the first place, but after spreading the compost out there's usually a small workload of 'weeding' the unwanted seedlings that pop up here and there.

An essential part of my composting set-up is the 'spare bin'. This was the original, and not very efficient, compost bin I had in the backyard 17 years ago. It's still extremely useful, because I always say that the minimum number of compost bins in any backyard should be two. Let me explain: I always get to the point in autumn where the big tumbler bin is chock-full. I then stop adding kitchen scraps to the tumbler bin and let it break down into compost (which takes three or four months, provided I keep on turning the tumbler bin over every few days). So this spare bin then becomes the bin where I keep on adding scraps during the months while the tumbler batch breaks down. Without a second bin, I'd stop recycling perfectly good kitchen waste for months on end, and that would be a criminal waste!

Now we're getting into the nitty gritty! A peek under the lid of the spare bin shows a couple of important composting lessons I've learned over the last few years. To get compost working well, you need to add a balance of 'wet' and 'dry' ingredients. Wet ingredients include scraps from vegies and fruit, which we have in abundance as we both do a lot of cooking using only fresh ingredients. However, 'dry' ingredients are in much shorter supply. They might include fallen leaves, shredded paper, old potting mix, or straw, for example. I've found the easiest way to supply dry ingredients to the compost is to add some straw mulch, each time I add another bin of scraps from the kitchen. Any old straw mulch will do, and here in Sydney sugar cane mulch is cheap and plentiful, so that's what I use both on my garden beds and in my compost bin.

When you get the balance wrong inside a compost heap, the process of breaking everything down slows down, either because it's simply too wet or too dry. The worms let you know whether you've got it right. They thrive in good going, and they are scarce when the mix is wrong.

The other magic ingredient in my compost bin is dolomite lime. I discovered a few years ago that my compost was too acid (probably due to the large amount of fruit scraps), so I've got into adding regular handfuls of dolomite to the compost bin to sweeten it all up. I just tested a sample of the latest batch, and it's still a bit too acid, around pH 5.5. Fortunately my soil is around pH 6.5, so when I dig in the compost to a garden bed for vegies, I add more dolomite to help raise its pH. A reading of 5.5, as shown here, still isn't that good of course, so I'll just have to keep on working on adding more dolomite over the next year!

Compost is wonderful for all garden plants, and this morning's 'harvest' of compost was prompted by the need to hill some soil around my potato plants. I simply didn't have enough soil to do the job, so I mixed it 50:50 with some compost. While I was at it I also pulled out the failed crop of Brussels sprouts and prepared that bed for planting zucchinis soon. After adding lots of compost, chicken poo, dolomite and digging it all into the soil, I'll wait a week or two before planting the zucchini seedlings that I'm raising from seed at the moment.

I love the way that composting is the very essence of the endless cycle of life, decay and regeneration here on planet Earth. I don't feel so bad about the prospect that one day I, too, will become compost returned to the earth. It just seems the natural order of things, and I wouldn't have it any other way.