With the gardening season picking up speed, it’s time to think about composting. And it’s not very complicated: any organic material will decompose when exposed to a little moisture and heat, either in a compost pile, a compost bin, or just spread around among your garden’s plants (surface composting).
However organic matter decomposes more quickly when there is about the same quantity of carbon-rich materials (called brown materials) and nitrogen-rich materials (called green materials although they are not necessarily green). It’s therefore useful to know whether a product is “brown” or “green” when you add it to the compost so you can blend in about equal amounts.
- fall leaves (preferably shredded);
- dead plants;
- used potting soil (from houseplants, container gardens, etc.);
- peat moss;
- wood chips and sawdust (in modest amounts);
- pine needles;
- nuts and shells;
- wood ash (in limited quantities);
- buckwheat hulls;
- cardboard egg cartons;
- coffee filters;
- hay and straw;
- paper (preferably shredded);
- cotton/wool/silk scraps.
- garden waste (tree and shrub prunings*, vegetables, herbaceous plants, deadheaded flowers, etc.)
- kitchen scraps (vegetable and fruit peelings, rotten fruit, etc.);
- leaves, stems and flowers of weeds;
- roots of annual weeds and perennial weeds without creeping rootstocks;
- lawn clippings;
- wilted cut flowers;
- coffee grounds;
- tea bags and herbal teas;
- aquarium water (from fresh water aquariums only);
- hair, fingernails;
- human urine (in limited quantities)
- animal fur;
- manure (cow, horse, chicken, etc.);
- ground up eggshells;
- bread, rice and other cereals.
*You can put even poisonous leaves, like rhubarb leaves, in the compost.
As green materials are usually far more abundant during the summer months than brown ones, many gardeners store up a good supply of bags of fall leaves, collected the previous autumn, to mix with green materials during summer and thus maintain a good balance. An alternative is to add shredded newspaper.
Don’t Compost These
There are products that can’t logically be composted: metal, plastic, glass, coated paper and cardboard and hazardous waste like chemicals and antifreeze. They should be recycled where possible or put out with the trash if not.
There are also organic materials that could be theoretically be composted if you are doing so on a large scale (such as in commercial and municipal composting), but that it’s better to avoid in the home compost pile/bin. There are two reasons for this. One is that small-scale composting doesn’t necessarily heat up enough to destroy all possibly harmful microbes or plant parts. The other is that some materials just decompose too slowly to be worth using. This is the case of the following products:
- animal fat;
- human and pet excrements;
- weed seeds;
- dairy products;
- roots of weeds with creeping rootstalks (horsetail, goutweed, Japanese knotweed, quack grass, etc.)
- logs and large branches;
- corncobs (unless ground up);
- oyster shells (unless finely ground up).
A Crash Course on Composting
There isn’t much to composting. It’s a pretty basic practice.
Composting can be carried out almost anywhere and any way, but for things to go smoothly, it’s best if the bin or pile is in sun (cool climates) or partial shade (hot ones) and placed directly on the soil (to allow earthworms and beneficial microbes easy access).
Ideally you need a large pile or bin (at least 35 ft3or 1 m3, more, if possible): the more material you have, the faster it will decompose … and thoroughly remix the contents every two to four weeks for aeration, as this boosts the oxygen level and speeds up decomposition.
There is no need for a commercial compost activator, but you can add a handful of soil collected in the garden to the pile when starting it: it will contain all the microbes necessary for good decomposition to begin.
Add water as needed: the compost should never be completely dry or sopping wet, but rather have the consistency of a moist sponge.
When the compost pile heats up (it may even release water vapor!), you’ll know it’s going full steam ahead. Many commercial composters are too small to reach the critical mass needed for intense heat to be produced: their materials will still decompose, but more slowly.
It can take as little as three to four weeks to produce a finished compost from a pile that heats up considerably (and that you turn to oxygenate every few days!), but for most gardeners, calculate it will take six months to a year to produce the final product.
You’ll know the compost is ready when you no longer recognize the components and it has the look and texture of dark brown garden soil. Also, it will smell like humus, that is, like a forest after the rain.