Compost is decomposed plant material that helps improve your soil by adding organic matter. It helps soil retain water and provides nutrients in a form plants can use easily. Beneficial fungi and microbes in compost also help your plants absorb water and nutrients from the soil. The process of making compost is actually a speeded-up version of what happens naturally on the forest floor or prairie.
Compost starts with equal portions of "greens" and "browns". Organisms that break down plant material use carbon from browns for energy, and nitrogen from greens as food. Typical greens are: fresh grass clippings, chopped garden debris, coffee grounds or manure. Some browns are: fall leaves, straw, wood chips or sawdust (but don't use chips or sawdust from pressure-treated wood). You should be sure grass clippings come from lawns that were not treated with pesticides or herbicides.
Hot Composting
Hot composting is a method that creates compost very quickly. The bacteria that help break down plant material generate enough heat to raise the temperate to as high as 140-160 degrees. This kills most weed seeds and pathogens. A critical mass of at least 3'x3'x3' is needed to really get the decomposition process going.
To begin a batch, first find or build an empty compost bin. Many P-Patches already have bins just waiting for you! Gather and mix equal parts of greens and browns. Fill your compost bin to the top with this mixture, but don't overfill it and never compress the ingredients to try to make them fit. That squeezes out needed air.
As you transfer your mix to the bin, add enough water to dampen it well, but don't drench it. The fungi, microbes and other critters responsible for decomposition need water and oxygen to live. Too much water pushes out all the oxygen, leaving you with a smelly mess! If the batch is too dry, the composting process will slow down or stop. Your compost should be about as damp as a wrung-out sponge.
Cover the top of your batch with a few burlap bags to help retain moisture. Also cover the bin with a piece of plywood to keep out rain and sun.
Tending your Compost
After a few days your new batch of compost will heat up as bacteria start munching away at plant material, consuming oxygen in the process. Fungi will also feast on the fresh mix. These microbes and critters need air to do their work. About once a week, add more oxygen by turning your pile into an empty bin, or if you only have one bin, remove the contents and then put them back in. Try to move the stuff from the top to the bottom, and vice versa. As you turn, add a little water if the mix appears too dry.
Your batch will seem to shrink as the ingredients settle and rot. I like to top off the bin with more fresh mix the first few times I turn a batch.
Your hot compost is finished when it has mostly stopped decomposing, does not heat up between turnings, and looks and smells like dark soil. The initial ingredients should be unrecognizable in the finished product. In summertime, a batch takes about 6 weeks to finish. In winter, it may take as many as 12 weeks. So plan ahead for planting or transplanting time.
As you might have imagined, collecting ingredients for hot compost all at once, then turning the whole batch every week for 6-12 weeks can be tedious and backbreaking work. There's got to be an easier way -- and there is! It's known as cold composting.
Cold Compost
Any dead plant material will eventually rot back to soil. It may take weeks, months, or even years. The only question is how long you're willing to wait, and how much effort you're willing to add to speed up the process. The process where you add plant material as it becomes available (rather than all at once) is called cold composting because the ingredients don't heat up.
You don't need a bin for cold compost -- you can start a pile in a corner of your garden. As you have plant material to get rid of, just add it to the top of the pile. You can chop material by hand, or just throw it on whole. If you find that you have a lot of fresh plant material to add at once, it wouldn't hurt to add some extra browns. The same balance of greens and browns technically still applies to cold compost piles, but you usually don't have so many greens to add at once that restoring the balance becomes a necessity.
Your cold compost will be ready to use in 6 to 12 months. To get to the good stuff, remove the top layer of material that hasn't decomposed yet. Use that un-rotted material as the base for your next cold pile.
Since cold compost doesn't heat up to kill diseases, seeds and rootstock, you will need to be a little more careful about what you put in a cold pile. Don't add weeds that have gone to seed, diseased plant material, persistent roots from berries or vines, or vegetables like tomatoes or potatoes that may sprout in the wrong places.
Trench or Pit Composting
If you don't have a compost bin handy, or don't have room for a cold compost pile, why not try composting underground?
In trench or pit composting, ingredients are buried in holes or a long trench and covered with soil. When you anticipate you will have lots of garden debris to get rid of (like at harvest time), dig a round hole or a long trench between planting rows about 8-12" deep. As you accumulate green material, chop it and mix it with some browns like fall leaves. Drop the mix into your holes or trenches until they're about half filled, then cover it with the original soil you dug out.
It's important not to bury the plant material too deeply since most biological activity occurs in the top 12" of soil. Some gardeners recommend rotating your open and cooking trenches with plantings in a 3-year cycle. However, each pit or trench should be ready to plant over in a few months. If you wish to plant sooner, try peas or beans since they have shallow roots that won't be damaged by the rotting process happening deeper down, and because they help trap nitrogen that might otherwise escape from the decomposing material.
Sheet Composting
Sheet composting is easier than trench composting because there's no digging involved.
Start your sheet compost with a mix of equal parts greens and browns. I prefer mixing the ingredients thoroughly, but you can use several 2-3" layers of greens and browns if that's easier for you. Spread your mixture in an 8-12" overall layer and water it down. You can cover the mixture with burlap bags and wait a few weeks for decomposition to begin, or you can plant directly in the new mix. The layer of materials won't be thick enough to retain heat, so seeds or roots won't be damaged. You can also plant a cover crop over the compost materials. Nitrogen-fixing covers like crimson clover, vetch, or fava beans are the best since they will help capture nitrogen released in the decomposition process. Rye or other grasses won't capture the nitrogen as well as legumes will.
Using Your Compost
Compost acts as a slow-release fertilizer and you can add it to your garden at any time. Before planting in spring, dig lots of finished compost into the soil. As plants grow throughout the summer, mulch between rows with it every few weeks (but leave a little space around plant stems). In the fall, add compost before sowing a cover crop. If you cover your beds in the winter, add compost to let it age well before spring returns.
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