How to - Techniques

The secret to making good compost

Find the right balance to create the ultimate gardener's 'gold'

The right "ingredients"
Controlled and speedy decomposition is all about balance. If your compost pile is too full of "browns"—compost lingo for carbon-rich materials such as dead leaves, straw and dead plant stalks—then your pile will be slow to decompose. On the other hand, if the pile is too full of "greens"—nitrogen-rich materials such as fresh food scraps and grass clippings—it will turn slimy and smell bad. The goal is to have equal amounts, roughly by weight, of browns and greens. The ideal carbon-to-nitrogen ratio for decomposition is about 30:1. Dead leaves (browns) have a C:N ratio of approximately 40:1 to 80:1, while fresh grass clippings (greens) have a ratio of 19:1. But there's no need to obsess: your eyes, nose and common sense will tell you if you've got roughly the right balance.

The other ingredient you should add to the pile is soil; it supplies starter micro-organisms—bacteria and other microscopic organisms that digest and excrete organic materials, breaking them down. Soil also masks the odour of food waste, which discourages pests from visiting your pile—and it's easier to keep pests out than to dislodge them once they've arrived.

Store-bought compost accelerators are generally nitrogen-rich to balance the bulk of compost materials—dead leaves—that are heavy on carbon. But if you're already adding a balance of green and brown materials, there's no need to include supplemental nitrogen.

Recipe instructions
To achieve even greater balance and the speediest possible decomposition, layer the browns and greens, and build the pile all at once. This works well when you've got a lot of grass clippings for greens and dead leaves for browns. I always keep a big bag of dead leaves by my bin—that way, I have a ready source of browns even in spring and summer. But who wants to stockpile rotting vegetables? Add them for greens as they become available.

Begin with a mixture of dead plant stalks—this loose, lower layer permits air circulation at the bottom of the pile, which is important to controlled decomposition. (A densely compacted pile may start to smell bad.) Then, add a layer (approximately 15 centimetres) of greens, such as coffee grounds, vegetable peelings and grass clippings. Sprinkle a 2.5- to five-centimetre layer of soil over the greens, and add a thick layer (approximately 30 centimetres) of dead leaves, straw or dried garden clippings. Repeat this layering process of greens, soil and browns until the bin is full.

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