Gardeners can make compost at home in a corner of the garden. It is a very forgiving process—and as long as only things that should go into the compost pile do, eventually it will work. As long as the pile does not have too much high-nitrogen ‘green’ material in it, it should not smell bad or be a nuisance, either.

In an untended forest or jungle, leaves and other plant materials fall to the ground and decompose—this creates a rich and fertile layer of compost and humus for future growth and is all accomplished without any human intervention. It is not neat, fast or pretty, but it has worked in nature for a very, very long time!

If you took a bag containing leaves, lawn clippings and ripped up newspapers and spread it out on the ground, eventually it would decompose just as it would on a forest floor. It would also be messy and the neighbors might complain if you made a habit of it, so a tidier solution would be to put the material into a pile. Ideally, the pile should measure at least a yard or so on each side—this not only keeps things neater around the garden but also helps facilitate the composting process.

This mound of decomposing vegetation is referred to as a ‘cold’ compost pile and—depending on what’s in it—in anywhere from a few months to a couple of years it will become compost. Nature will do all the work if given enough time and some occasional rainfall. One very simple form of composting involves taking leftover leaves, stems and roots after a fall harvest, putting them in a pile and then digging out the compost that develops over the winter for use in the spring.

Depending on local conditions, this method might have to be modified to include a few different piles—each pile can then be allowed to sit for a year or longer. Ideally, each compost pile should measure about a yard or more on each side, because piles that are too small don’t heat up as well.

Large piles are hard to stir but they need to be stirred more often than small piles because it is important that the material at the core be rotated with the material on the outside for even composting.

There are ways to make the process faster and to avoid unpleasant aromas. While decomposing material in the forest can stink and no one will care, if you smell up your backyard you might have a problem. If too much ‘green’ material is added, the pile can start to smell. When plant material decomposes, it can be processed by either air-loving (aerobic), or air-hating (anaerobic) bacteria.

A wet pile of dark green spinach leaves (green material) will quickly become host to anaerobic bacteria and start to rot, giving off an unpleasant smell. If that same pile was mixed with fall leaves (brown material), then the moisture would be better distributed and the mixture would have better aeration.

Aerobic bacteria would dominate and the resulting mixture would give off a sweet earthy smell while it converted into compost. If too much brown material is added, however, decomposition will slow and the process will take longer. When in doubt, keep in mind that too much brown smells better than too much green!

Brown materials generally have a carbon-to-nitrogen ratio of greater than 30 to one. Leaves, newspaper, cardboard, sawdust, straw and anything tree- or sugar-related are usually considered brown materials and they will all take a long time to decompose if left in a pile without green materials.

If too much brown material is added to a pile composting will slow, but brown materials do help with structure and odor control. If your compost pile starts to smell, add more browns and stir the pile.

Green materials generally have a carbon-to-nitrogen ratio of less than 30 to one. In other words, they contribute more nitrogen for the amount of carbon that they contain than brown materials do. Grass clippings, vegetable or fruit food scraps, coffee grounds and green leafy material are all greens.

These will decompose quickly if left in a pile without brown materials, but they also tend to stink and rot in the process. Be careful not to put too much citrus in a pile at once, as the acid can hinder microbial action.

Putting a layer of browns over a new layer of greens will help keep the pile from smelling unpleasant. Ideally, the compost pile should have a light earthy aroma—foul odors are an indication that something isn’t right. Add browns and stir to help correct this kind of imbalance.

Leaves, stems, roots and used potting soil can all be put into the compost pile, but you should avoid any plant material that has had problems with insects or disease or that has been treated with pesticides. A cup of diluted molasses or any other sugar syrup can boost microbial growth, but it should be supplied to the center of the pile and buried to avoid attracting ants and other pests.

Eggshells and coffee grounds are two leftovers from the breakfast table that can be composted and gardeners can often pick up used coffee grounds for free from local coffee shops. Do not put any fatty, oily or greasy food scraps or material into the compost and avoid meat and meat products. Dog, cat and human waste can all carry dangerous pathogens and should not be used either.

To speed up the composting of brown material and to keep green material from stinking, use approximately equal amounts of each and mix well. Smaller pieces compost faster than large pieces do, in part because of the increase in surface area for the bacteria to work on—this is why even though a log and sawdust are made from the same material, sawdust can be composted in weeks or months while a decomposing log can take years or decades.

A pile of 50/50 brown-to-green material will compost faster and more pleasantly than a mix containing too much of one or the other. Due to differences in density and carbon values the ratio might need to be adjusted to some degree depending on what materials are being used—as a rule of thumb, if it starts getting funky, add browns and stir. If it isn’t doing anything, add greens and stir.

The biological agents involved in this process need air and moisture—the pile should be kept damp but not wet and to give the bacteria air you should stir the compost pile occasionally. Light watering and stirring will speed up the composting process.

If the pile doesn’t start to heat up in the next couple of days, it is an indication that something is off. It could be that there isn’t enough material in the pile, the composition of the pile is off, it isn’t moist enough, it’s too moist or it needs stirring. A compost pile that doesn’t heat up is called a ‘cold’ compost pile—it will still make compost, but it will take longer than a ‘hot’ one will. When in doubt stir the pile, as stirring corrects a multitude of problems and is an easy fix.

If the compost mix, moisture content and air supply are all okay (or at least close), a new pile should start to heat up and become a ‘hot’ compost pile. A pile with an internal temperature between 120 and 140°F is ideal, but temperatures might reach as high as 160°F. As composting continues the temperature will drop as more material converts into compost.

Hot composting does have some advantages over cold composting—it is faster and some pathogens will be killed from the heat generated—but temperatures that are allowed to become too high can kill beneficial bacteria and microorganisms as well, so hotter is not always better.

Once the compost is ready, it should be a dark, earthy-smelling material. To remove any debris (or walnuts—my compost pile is a favorite burying spot for the local squirrel population), the compost can be run through a piece of grating. The finished product should be very similar to commercially bagged compost. If there are still identifiable pieces in the mix the compost is still immature (or at least those pieces are).

Eventually compost will complete its decomposition and convert into its stable form, which is known as humus. Humus is so stable that it can remain unchanged for hundreds, if not thousands of years. However, since decomposition is complete humus contains little nutrient value, although it still provides for a less compact soil density and general soil improvement. Humic acid, fulvic acid and humin are all humus extracts.

Making compost is not difficult—nature does it all the time. If you help the process along by using a properly aerated and moistened mix of the correct proportions, a compost pile can easily be set up in your backyard. Making your own compost will certainly save you money on purchasing and transporting bags of store-bought product. A hot compost pile is a gardening accomplishment to be proud of, but even if it doesn’t heat up nature will eventually turn it into cold compost—it will just take a bit longer.