How to Make Compost
Garden compost is a crumbly, dark, organic material, processed from waste materials from the kitchen and garden. It is made by soil bacteria and other microorganisms, which break down and rot the raw materials. Grass clippings can be used “raw” as a mulch, but are much more effective once composted. Building the pile Your role in making compost is to provide soil organisms with warmth, moisture, and a good mix of materials. Placing bins on bare soil allows these organisms to get inside. Alternatively, add a spadeful of compost from an old pile, or soil, for every 12 inches (30 cm) of material.
Shredded materials will rot down faster than unshredded ones. You can chop most stems and leaves up with a spade, but it may be worth renting a shredder in fall to break down heavier woody material and leaves. It is best to store your compost in a bin; either buy one, or make your own using mesh or wood. A pit is another possibility, but it will be hard to empty and may become waterlogged in the winter. Whichever type of bin or pile you use, it will need a lid to keep out rain.
In theory, you should fill your compost bin with a good blend of materials in as short a period as possible. In practice, it is likely that the bin will take time to fill up. Therefore it probably won’t generate enough warmth for thorough composting; weed seeds and roots may survive, as may organisms in diseased material. Large-scale municipal composting reaches temperatures that eliminate these problems, but small volumes of homemade compost cannot match this, so be careful what you add to your heap.
If you cannot achieve the ideal blend of ingredients, you could try using “activators.” These nitrogen-rich materials help to break down woody materials, and can be useful when you have too little soft green material. Alternatively, add a thin layer of manure, mushroom compost, or a sprinkling of nitrogen-rich fertilizer to every 6 inches (15 cm) of woody material. Adding lime is sometimes recommended, but is usually unnecessary, unless you are composting lots of shredded conifer prunings or waste fruit, which can be very acidic.
Ready to Use?
Turning the compost can speed up the process. Empty the bin and mix the contents, adding water to dry material before returning it to the bin. To check the progress of your pile, pull back the upper layers to see if the fibrous material is breaking down. If not, it may be too dry, or it may need more soft, green material, such as lawn clippings, to add nitrogen. If you have a small household or modest garden, your compost may not turn out to be the ideal uniformly crumbly, brown material you had hoped for. Instead, it will probably have twiggy and semi-rotted parts mixed in with a dark brown mass that smells like damp woodland. Pick or sift out the unrotted components, and add them to your next compost batch; they will rot down eventually. Bad smells indicate compost is too wet—turn it and add fibrous material. A layer of well-rotted compost from another bin or a layer of spent potting mix will also help seal in odors.
Getting the right balance is important—ideally 20–50 percent green, leafy material, and the rest more fibrous, woody material. In practice, you will have different materials at different times of year; do what you can with what is available and the materials will balance out over time. The main point is to try to prevent the bin from being dominated by one ingredient.
Put It In:
- Vegetable kitchen waste
- Weeds that haven’t gone to seed
- Grass clippings (These provide nitrogen and other nutrients for the microorganisms. They are wet and soft, so must be mixed with fibrous material.)
- Shredded paper or cardboard
- Eggshells and carrot peelings
- Spent bedding plants
- Decaying stems of perennials
- Twiggy prunings
- Fallen leaves (These provide tougher, carbon-rich material with less nitrogen. If you don’t have time or space for leaf mold, fallen leaves can be included.)
Leave It Out:
- Material that is diseased, damaged or contaminated with weed killer
- Weeds carrying seeds or with roots that might survive composting, such as dandelions
- Cat and dog droppings, which may harbor harmful organisms
- Kitchen waste containing animal materials, such as scraps of meat, which can attract rats.