Compost is simply organic material broken down by microbes, fungi and worms into a dark, crumbly, nutrient-rich material you dig back into the soil. Getting a heap going that actually breaks down well, rather than turning into a smelly, slimy mess, comes down to a handful of basics that hold true in most New Zealand backyards.
The core of it is balancing "greens" and "browns". Greens are nitrogen-rich, wetter materials: vegetable scraps, coffee grounds, grass clippings, fresh garden trimmings. Browns are carbon-rich and dry: fallen leaves, shredded paper and cardboard, straw, twigs. A rough rule of thumb is roughly equal parts by volume of each, leaning slightly toward more browns if anything, since a heap that's too green-heavy turns wet, compacted and smelly, while one that's too brown-heavy breaks down very slowly. Layering the two as you add material, rather than dumping all of one type in at once, makes it easier to keep the balance right.
What to leave out matters as much as what goes in. Meat, dairy, fat and cooked food attract rats and other pests and smell bad as they break down, so they're best kept out of a standard home compost heap entirely. Diseased plant material, especially anything with blight, clubroot or similar, should go in general waste rather than compost, since home compost heaps rarely reach a high enough temperature for long enough to reliably kill off plant pathogens. The same goes for weeds that have already gone to seed: an average backyard heap won't get hot enough to kill the seeds, so you end up spreading them right back through your garden in the finished compost.
For a small garden or apartment without much outdoor space, a tumbler bin is a good fit: it's enclosed, easy to turn, which speeds up decomposition and keeps it aerated, and doesn't need a big footprint. Turning a tumbler two or three times a week keeps oxygen moving through the material, which is what keeps the process aerobic and smell-free. Bokashi is the option for genuinely space-constrained situations, like an apartment with no outdoor access at all: it's a sealed kitchen bin system that ferments all food scraps, including small amounts of meat and dairy that wouldn't normally go in a compost heap, using a bran inoculated with effective microbes. It doesn't produce finished compost on its own; after a couple of weeks of fermenting, the contents still need to be buried in soil or added to an outdoor compost system to fully break down.
How long it takes depends heavily on method and effort. A well-managed, regularly turned heap or tumbler with a good green-brown balance can produce usable compost in as little as two to three months over a warm season. A heap that's left alone, rarely turned, and gets whatever scraps show up regardless of balance can take six months to a year, and won't heat up enough to break down tougher material like woody stems quickly.
A healthy heap smells earthy, not sour or rotten, and it should be damp like a wrung-out sponge, not soggy or bone dry. If it smells sour or slimy, it's usually too wet and too green: add dry browns and turn it. If it's not breaking down at all and smells like nothing, it's usually too dry: add water and some fresh green material. A heap that's genuinely working generates real heat in its centre, noticeably warm to the touch, which is a good sign the microbes are active.
A healthy heap smells earthy, not sour or rotten, and it should be damp like a wrung-out sponge, not soggy or bone dry.
Finished compost is a soil improver, not a growing medium on its own. Dig or mix it into garden beds and containers to improve structure, water retention and nutrient content, rather than trying to grow directly in pure compost, which is generally too rich and unevenly textured to support seedlings well by itself.