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Learn how to compost—which is decomposed, well-rotted organic material from yard debris and kitchen vegetable scraps. This crumbly, nutrient-rich organic matter improves soil in a number of ways. We’ll show you how ot make “cold” and “hot” compost, and avoid any compost problems.
What Is Compost?
Compost is a nutrient-rich, soil-like material comprised of decomposing organic matter—most often made up of your own fallen leaves, grass clipping, plant debris, vegetable scraps, and yard waste. The key idea behind composting is that the materials and waste that you might normally throw away can actually be recycled to help plants grow, delivering better harvests and flower blooms.
Also, compost fixes soil problems. If the key to a successful garden is good soil (and it is), compost is the gardener’s secret weapon. It has been lovingly called the gardener’s great equalizer because of its ability to amend soil. Is your soil too sandy? Compost will hold sand particles together so they can absorb water like a sponge. Troubled by hard clay soil? Compost attaches to particles of clay, creating spaces for water and nutrients to flow to plant roots. Even in perfectly loamy soil, compost brings something to the table: a ton of nutrients.
In community gardens, you may see a series of several bins filled with organic matter in different states of decomposition, but don’t let a professional system like that intimidate you! It’s a common misconception that you need to have a large outdoor space in order to practice composting. You can make your own compost in a space as small as a patio or balcony.
Are Compost Bins Necessary?
At its most basic, a composting system doesn’t need to consist of anything more than a pile in the corner of your yard. As long as the pile ends up being about 4 feet high, 4 feet wide, and 4 feet deep, it should be successful at decomposing everything you throw at it.
Most compost piles, however, have a dedicated structure that keeps it all contained—something like a cube made of wood pallets or even a purpose-built plastic compost bin. Here’s how to make your own compost bin! Fancy bins with multiple layers and sifters are nice, but not necessary.
Most organic materials can be composted. As mentioned above, this includes things like fallen leaves, grass clippings, shredded newspaper, wood chips, vegetable scraps, and so on.
In addition to the ingredients mentioned above, any of these items may be added to a compost pile:
Coffee grounds and loose tea or compostable tea bags (note that most tea bags are not fully compostable, so tear or shred them before adding to compost)
Dry goods (crackers, flour, spices)
Pasta (cooked or uncooked)
Bedding from chicken coops or from small mammal pets (guinea pigs, rabbits, hamsters, etc.)
What CAN’T Be Composted?
Materials that you should NOT put in your compost pile include inorganic materials (rock, glass, metal, plastic, etc.) and animal products, like bones, seafood, meat scraps, dairy products, and grease. (Eggshells are an exception, since they break down easily and are a good source of calcium!) Additionally, don’t add dog or cat waste (nor kitty litter) to your compost pile, as these may contain parasites or other nasty things that may not get completely decomposed.
Also, if you’re collecting grass clippings from the neighbors, make sure they don’t use weed killers on their lawns. Those chemicals take forever to break down and will negatively impact any plants you use your finished compost on.
4 Essential Ingredients of a Healthy Compost Pile
A productive compost pile needs four things:
Brown matter (“browns”): This is carbon-rich material such as straw, wood chippings, shredded brown cardboard, or fallen leaves.
Green matter (“greens”): These are nitrogen-rich materials like grass clippings, weeds, manure, or kitchen scraps. Greens should have carbon-to-nitrogen ratio of about 30:1.
Water: The pile should be kept consistently moist, especially important if you add lots of dry leaves or hay. Usually rainfall is enough to keep it damp, but in a dry summer you might have to spray it with water.
Air: Oxygen is necessary for aerobic micro-organisms to survive. They are the ones doing all the work of turning your garden waste into black gold.
Keep in mind that color isn’t always a reliable indicator of what is a green or a brown. For example, fresh grass clippings—even when spread out and left to dry—are still considered a “green” ingredient even though they’ve turned a brownish color, because really all they’ve lost is water. On the other hand, straw is always considered a “brown” because before the main stems had died and much of the plant’s nitrogen had gone into the seeds as protein before it was harvested.
Compost decomposes much faster if you chop the ingredients up, so shredding woody materials and tearing up cardboard speeds up the process because there is then more surface area exposed to the microbes that decompose the organic matter.
Air is vital to the composting process, so it’s important to mix the ingredients in together, and never squash them down. Many people turn their compost piles several times over the summer. Turning your compost helps speed up the process of decomposition, but is not necessary as long as the pile isn’t completely compacted. It will all rot eventually!
Composting Methods: Hot vs. Cold Composting
1. Hot (or “Active”) Composting
The most effective way to produce rich garden compost is to create a hot, or active, compost pile. It’s called “hot” because it can reach an internal temperature of up to 160°F (71°C) and “active” because it destroys—essentially by cooking—weed seeds and disease-causing organisms. A temperature of about 140°F (60°C) is what you should aim for in a hot, active compost pile. (The size of the pile, the ingredients, and their arrangements in layers are key to reaching that desired outcome.)
Use the Right Ratio
When making a hot compost pile, you want to have 2 to 3 times more brown materials than greens, at least initially, although some more greens can be added as the compost cooks.
For most gardeners, the biggest challenge is therefore collecting enough brown materials and not just piling in loads of greens, which will result in a soggy, smelly mess. For example, never add lots of grass clippings in one go, as they will just form a slimy, matted layer.
On the other hand, avoid adding too much brown matter at once, too. Dumping your fall leaves into the compost heap all at once can really slow things down! Add them in modest qualities along with fresh green ingredients. Or, compost them separately over one or two years as leaf mold. See how to make leaf mold here.
Alternate layers of brown and green matter when building your hot compost pile and add a few shovels full of garden soil to contribute those essential soil microbes. The more green matter, the hotter the pile will get and the faster it will decompose. Heat also helps to kill off disease spores and weed seeds.
How Big Should the Compost Pile Be?
A hot compost pile should be at least 3 feet in diameter, though slightly larger (4 feet) is ideal. The pile will shrink as the ingredients decompose. Consider keeping the contents in place with chicken netting; wooden sides would be even better to keep the pile contained.
Making a Hot Compost Pile
Cutting up or shredding materials helps speed up the process.
Pile the ingredients like a layer cake, with carbon-rich materials (browns) on the bottom. Placing twigs and woody stems here will help air circulate into the pile.
Next, cover the layer with soil.
Add nitrogen-rich materials (greens), followed by soil. Repeat the alternating layers of greens and browns until the pile reaches 2 to 3 feet high.
Soak the pile at its start and water periodically; its consistency should be that of a damp (not wet) sponge.
Add air to the interior of the pile by punching holes in its sides or by pushing 1- to 2-foot lengths of hollow pipe into it.
Within a week or so, your compost pile should start cooking. Check the temperature of the pile with a compost thermometer or an old kitchen thermometer. A temperature of 110°F to 140°F (43°C to 60°C) is desirable. If you have no heat or insufficient heat, add nitrogen in the form of soft green ingredients or organic fertilizer.
Once a week, or as soon as the center starts to cool down, turn the pile. Move materials from the center of the pile to the outside. (For usable compost in 1 to 3 months, turn it every other week; for finished compost within a month, turn it every couple of days.)
See our new video on making super-fast compost!
2. Cold (or “Passive”) Composting
Cold, or passive, composting requires less effort than hot composting. You essentially let a pile of organic matter build and decompose, using the same types of ingredients as you would in a hot compost pile. The difference is that you don’t spend time turning the pile or carefully managing the ratio of greens to browns.
Cold composting requires less effort from the gardener, but the decomposition takes substantially longer—a year or more!
Making a Cold Compost Pile
To cold compost, simply create a pile of organic materials that you add to as you find or accumulate them. If possible, alternate layers of browns and greens, mixing in a few shovelfuls of garden soil, too. Since they’ll take longer to break down, bury kitchen scraps in the pile’s center to deter curious insect and animal pests.
NOTE: Avoid adding weeds or diseased plant materials to a cold compost pile, as the pile will not reach the high temperatures capable of killing weed seeds and diseases. (In fact, weeds may germinate in a cold pile.)
3. Vermicomposting (Composting with Worms)
Yet another composting method is something called “vermicomposting,” which employs worms to do the hard work of breaking down your organic waste and scraps. Vermicomposting is probably the most space-saving composting method, since it can be done in something as small as a 10-gallon plastic tub. Getting a vermicomposting system started is the hardest part, since you’ll need to buy materials and get yourself a sufficient number of worms to begin with (and not all worms are suitable!), but after that, all it takes to maintain a vermicomposting system is feeding it regularly with kitchen scraps.
Composting doesn’t have to be messy, stinky, or complicated, but sometimes problems do arise. Usually, it’s easy to get your compost pile back on track.
What Should I Do If My Compost is Too Wet?
Too much green matter can result in slimy, wet compost piles. Avoid soggy piles by alternating wetter ingredients (such as fresh grass clippings) with drier and more fibrous ingredients (such as dry leaves, cardboard, and woodier crop residue). The resulting mix should be damp but not sodden. You can also sprinkle wood ash onto your heap but, importantly, it must be wood ash and not coal ash.
Why Does My Compost Smell Bad?
If a foul odor emanates from your compost bin or pile, flip the compost to introduce more air. Mixing the compost not only gives it plenty of air but results in a finer end product that is easier to spread. A good compost heap has a slightly sweet compost-y smell. If it smells sour or rotten, then it either has too many greens or is too wet.
How Do I Keep Pests Away From My Compost Pile?
Avoid cooked food waste and animal products like meat and dairy, which attract rats and other pests. Try burying veggie scraps or other food waste in the center of your pile so that it’s not as accessible to pests. If rodents are a problem, ease off adding potato peelings, which are a favorite snack.
Can I Compost Weeds?
Composting weeds is fine as long as the weeds haven’t yet set seed. A hot compost pile should be able to cook the seeds to make them inert, but it’s still a risk. In any case, avoid invasive perennial weeds such as bindweed and black swallow-wort—these are better off disposed of in the trash!
See how video on how to fix composting problems.
Take the plunge and get composting! You’ll feel great doing it. Or, if you’re already composting, share your tips for supercharging your compost!