Nothing does more for a garden than good compost. It's the best way to improve soil and create a perfect home, teeming with life, for the roots of your plants. But what is compost, exactly? And how do you get it?
If you've walked in the forest, you've probably kicked up leaves and seen the layer of light, fluffy, brown humus -- decayed plant and animal matter --at the top of the soil. It is essential to plant life, in forests and everywhere else.
Compost is humus too, but created from the leaves, weeds, grass clippings and other plant waste that every garden provides. The actual compost-makers are the same bacteria, fungi, arthropods, insects, earthworms and other living things that make humus in nature. All we gardeners do is set them to work in a compact space that's convenient for us and provide them with supplies of food, water and oxygen.
If you carefully manage the community of composters, you will get usable compost faster and more reliably. But if you don't bother, compost will happen anyway. It will just take longer.
So, let's get started:
Choose a spot. Make your compost where it's handy, both for adding material and for harvesting the finished product. Since a compost pile is rarely the loveliest thing in the garden, tuck it away in a far corner, in back of the garage or behind a hedge or shrub. In a small garden with few nooks, consider a tidy covered bin (which will also deter animals). You will need a space at least three feet square and high; smaller piles don't reach critical mass. The process will take less square footage and be more efficient in a bin that encloses it on at least three sides. But be sure that there is room at the opening for you and your wheelbarrow when you dig finished compost out.
Provide a balanced diet. Different creatures in the compost pile have different food preferences. Some consume material higher in carbon, such as dead leaves and twigs; others go for material higher in nitrogen, such as fresh green foliage and grass clippings. Compost scientists have determined that the most efficient ratio is about two parts carbon-rich material to one part nitrogen-rich material. For garden purposes, exact proportions aren't essential. Just bear in mind that you want more brown stuff than green stuff and aim for variety.
Collect your leaves. A fine source of carbon-rich material arrives free every autumn: the leaves that fall from the trees. Dead leaves alone are a good start on a compost pile, though you'll get more action if you mix them with grass clippings and other green stuff. Since gardens create so much green waste during the rest of the year, many gardeners collect leaves in fall and keep a stash near the compost pile for spring and summer. Keep leaves in a pile or in plastic garbage bags (where fungi may start breaking them down).
Forage in the kitchen. A lot of kitchen waste is fine food for a compost pile: fruit and vegetable peels, cores and trimmings; coffee grounds (including paper filters) and tea bags; too-old produce from the refrigerator drawers; eggshells (which eventually release useful calcium). But don't include meats or dairy, bread or oils (which rules out dressed salads).
Add dirt. The organisms that will make your compost -- or their eggs -- are already present in healthy soil. A couple of shovels full will get a new pile going. Bacteria and other creatures that find a food supply will start to reproduce and create a community of breakdown artists. For an extra good start, beg a good gardener for a gallon or so of already-busy compost.
Add water. Start your pile off with a good soak and try to keep it about as moist as a damp sponge. Rain will help, but plan to water the pile when it's dry or hot.
Add air. The compost-makers need oxygen to reproduce and feed. An airless compost pile caters to the wrong kind of bacteria, which stop the useful decay and produce a stink. So to aerate the pile, turn it over with a garden fork, mixing it and fluffing it, every few weeks or more often. This also will assure that all the material gets broken down.
Wait. It will take several months for the whole array of composting creatures to work over a new compost pile. The time will depend on the climate (the process slows or stops during cold weather or when the pile dries out), the mix of ingredients, how much you fuss and many other factors. Start checking the interior of the pile for doneness after about four months. Once you have some composting experience, you'll get a feel for how long it takes in your garden.
Harvest. Compost is done when it is dark brown and fluffy and most of it is no longer recognizable as the leaves, stalks or rinds you started with. It should have a clean, earthy smell. You should find earthworms, millipedes and other bugs that are at the top of the compost-pile food chain. In open piles that aren't turned often, the good stuff will be in the middle. You will always find undigested chunks; just toss them back in for further work. Some people sift compost to a fine, regular texture, using a special compost sifter (or a milk crate). Others are content to use chunky compost.
For more information on composting, see the University of Illinois Extension's compost web site.
Fine-tune your compost pile:
If you are willing to tinker, there are a number of ways to make the composting process faster and more efficient.
Turn more often. More oxygen permits more reproduction for faster decay.
Add smaller pieces. Bacteria -- the first shift of composters -- feed and reproduce on surfaces. Smaller pieces have more surface area for their volume. So if you shred or cut up the materials you add, they will start breaking down faster. Large sticks and chunks of wood may not break down for years.
Make a bigger pile. More volume supports a larger population of bacteria and fungi. It also holds heat more efficiently. A large, moist, airy pile of fresh material may actually start to smoke; that's because in the early stages, fast-reproducing bacteria generate heat as they feed. Only a large compost pile is likely to get hot enough -- at least 160 degrees Fahrenheit -- to kill weed seeds or kill disease organisms. But don't make the pile so big you can't manage to turn it regularly.
Expand your empire. Some composters, not content to make one batch at a time, keep three rotating bins: one "current" pile to which they are adding material; one that is full and "cooking"; and a third that is finished and ready to use.
Get the gadget. To maintain the range of 110 to 160 degrees Fahrenheit in which composting bacteria work most efficiently, a hard-core tinkerer will want a $20 compost thermometer.
Do add to the compost pile:
- Dried Leaves
- Grass clippings
- Flowers, leaves and stems from deadheading, pinching back or tidying up
- End-of-season annuals and vegetables
- End-of-season straw mulch
- Weeds (but only if they have not set seed)
- Vegetable and fruit scraps, cores and peels
- Coffee grounds and tea bags
- Manure from cows, goats, horses or chickens
Don't add to compost pile:
- Dog or cat waste
- Fats and oils (including salad dressings)
- Baked goods (including pizza)
- Dairy foods
- Weeds with seeds
- Diseased plants
- Sticks or woody branches more than 1/8 inch in diameter