Compost good! Must have more compost! If you've been following our blog, or any gardening blog for that matter, you've spent considerable time digging the earthy-smelling gardener's "black gold" into your flower and veggie beds. You're not just behaving like a mindless garden zombie—you're aware that decomposing matter is good for plant nutrition. You might not know exactly why, but you don't have to be a biochemist to understand that compost loosens up compacted soil, helps retain moisture, and releases nutrients that feed your plants. Here's an overview of how to compost, how it’s made and applied, and how it helps our gardens grow.
Digging up compost's dirty past
First, let's take a look at the name. Compost is a derivative of the Latin "com-" or, more specifically, compositus, meaning "placed together." Appropriate, since we add all sorts of stuff to a compost pile...so it can decompose. But even as the individual materials break down, they come together once again to create a community of microscopic organic life.
Latter Medieval English and French languages applied the root comp to compost ("mixture of leaves and manure"). "Compote" and "Compost" were once interchangeable. (Come on, admit it! Whenever you see "compote" on the menu at a fancy restaurant, images of crumbly soil, rotting leaves, and poop dance through your thoughts. Amirite?)
There's a bit of confusion as to who first used the term as a verb (Etymonline.com isn't perfect) or when the term "manuring with compost" was bandied about, but the intentional act of enriching crops using decomposing biological matter predates so-called modern language. ("Manuring" is an interesting application, implying that manure isn't so much a word for livestock waste as it is for natural soil improvement.)
According to the University of Illinois Extension, "The Bible and Talmud both contain numerous references to the use of rotted manure straw, and organic references to compost are contained in tenth and twelfth-century Arab writings." But a thousand years before baby Moses came down the mountain with God's iPod prototypes, Sumerian clay tablets made mention of manure as an agricultural amendment.
The purpose of garden compost
Garden compost is a vegetable-based matter that's been exposed to conditions suitable to host an ecosystem of bacteria, bugs, and fungi. As these microbes and critters feed off the decaying material, they produce nutrients that benefit plants directly, or that encourage the growth of new organisms that help plant roots better access and absorb nutrients and water. Compost builds a web of life in the soil, and that web actually binds soil elements together.
You need less compost than you think
Good soil has humus—old, inert, broken-down organic matter— and minerals, and nutrient-rich, mature compost. If you're establishing a new garden, it might be heavy on the first two, requiring more "fresh" material.
The general rule is to till one to four inches of finished compost into the top six inches of your soil; less if you have a lot of clay, more if yours is loose, depleted sandy soil. You can also side-dress growing plants with smaller amounts of compost, gently working it into the surface with your fingers. Compost takes many years to break down fully, and as long as it's still present in the soil, it continues to prevent compaction and improves drainage. It's most effective in its first two years when it's still actively contributing to the microcosm in your soil. After it peaks out, it's time to add more.
Creating a balanced compost ecosystem
The four main components of a compost pile are nitrogen, carbon, oxygen, and water. A healthy balance reduces odors, catalyzes proper core temperatures, and speeds up decomposition. In "garden-speak," nitrogen-rich materials are referred to as "green" ingredients, where the bulky, high-carbon matter is "brown."
Brown materials tend to be dead, dry organic matter, and decomposing "green" stuff turns into a slurry as it rots. Brown materials add "loft" to compost piles, preventing large masses of dense, rotting green stuff. A ratio of two or three parts brown to one part green is the go-to recipe for a well-balanced compost pile. Areas with high humidity might hold tight to the 3:1 ratio, while gardeners in the Gobi might start at 2:1 and add dry matter as needed.
Nitrogen-rich "green" compost ingredients
- Compost-friendly animal manure
- Fruit (though leathery peels are often categorized as brown)
- Green leaf and lawn trimmings (shred tougher, larger leaves)
- Cooked vegetable scraps
- Coffee grounds
Carbon-rich "brown" compost ingredients
- Untreated sawdust or wood chips
- Shredded newspaper, paper bags, or cardboard
- Chopped straw
- Dog and cat hair
- Tea bags and coffee filters
- Brown deciduous leaves
Note, some guides will refer to a C:N (carbon to nitrogen) ratio, which would be between 25:1 and 30:1 in an ideal compost system, but this formula is best used to understand the ratio within a given ingredient. For example, wood chips have a 400 to 1 C:N ratio, while fresh lawn clippings are 20 to 1. You'll need a lot more high-nitrogen material to balance an overload of wood shavings, but only a few handfuls of dead leaves (60:1) to balance a handful of cut grass.
But none of this takes into account moisture balance or the fact that most of us aren't going to separate our soggy alfalfa sprouts from our peanut shells, so the 2:1 brown/green ratio by volume is the easiest to use and understand.
Why compost piles need turning
The best finished compost has the same consistency, at the same stage of decomposition. Turning your pile loosens the material for better oxygenation, and ensures the stuff on the edges passes through all the right microbiomes.
Bacteria metabolism raises the pile's internal temperatures as high as 160°F. Some bacteria species are specialists, creating conditions ideal for specific fungi and more advanced beneficial insects (called decomposers). If you want a very readable but detailed explanation of the organisms that help turn your yard waste into nutrient-rich plant candy, check out this page.
In the meantime, here's the TL;DR:
Compost goes through several heat stages each time it's turned. Once the last of the fresh material has spent time at the pile's core, the temperatures will stabilize, but the process continues, making way for different decomposer species to set up shop. At this stage, the compost is in the "maturing" phase, and for the most part, should be left alone until you're ready to apply it to your garden.
Layer cakes and garden salads: Composting styles
You're probably wondering when we're going to get to the fun part when we talk about DIY compost bins and store-bought tumblers. Hold onto your horse manure, kids; first, you'll need to know how different composting techniques affect the speed by which the material breaks down.
- Requires separate levels of green and brown materials in equal amounts
- Must be mixed up anyway to incorporate outlying areas
- Difficult to evenly distribute moisture and heat
- Requires less-frequent turning
- May require nearby storage of brown material to offset green in the growing season (and vice-versa)
- Perfect for the anally-retentive gardener or Jenga enthusiast
Freeform passive piles
- Brown and green material is added somewhat willy-nilly
- Prone to imbalances, but easily corrected
- Rarely (if ever) turned
- Takes longer to break down
- Finished compost can be screened out, and the rest returned to the pile
- Separate piles for fresh, "cooking," and curing compost
- More organized
- Less (or no) time waiting between "batches"
- Takes up more room
- Some assembly required
Hot, accelerated piles
- Great for reducing harmful microbes in manure
- Maintains a fairly consistent heat period
- Fast turnover (literally and figuratively) time
- Some gardeners feel this method destroys too many beneficial microbes
- Regular turning required
Find the right compost containment system for your (yard) work ethic
There's nothing wrong with keeping a free-ranging, commando-style loose pile of duff somewhere on your property, but a little structure can (and sometimes can't) keep your yard tidy. Here are the most popular off-the-shelf or do-it-yourself "composters."
Hardware cloth cylinders
You can make one of these in minutes. Drive three or four rigid stakes into the ground, and run a course of 1/4" hardware cloth around the inside. Secure the mesh to the stakes with sturdy wire or cable ties, lining up the edge of one end to a stake to serve as a "door." Add compostables as you go, and when it's full, start another cylinder. You can open them up to rake out, mix, and refill as needed.
These are usually molded plastic square or somewhat pyramid-shaped containers with a lid, ventilation holes, and some way to access the finished compost at the bottom. They're a pain to maintain, but they tend to heat up rather quickly, so even if you can't easily turn your compost, you won't wait around forever to reap the rewards. But what sifts down to the bottom tends to be pretty soggy, as the condensation on the container's interior walls drips downward. If you can't turn the compost, go for the layered technique.
Three-stage compost bins
These require the most up-front work, but in the end, are the most efficient. The classic design calls for a 12-foot long wood-slatted rectangle divided into three bins. The front of each is walled off by slide-in boards. New material goes into the first bin; when this is full, the material in the third is usually ready to "harvest." The second bin, full of "rested" material, gets moved over, and the fresher stuff takes its place. The three-bin system works great if you only want to bother turning your compost as you transfer it, but if you want to be more hands-on, it's reasonably easy to get in and get it done.
Okay, these are pretty cool. Built from plastic barrels which either rest on the ground or suspend from frames, these babies rely on heat and frequent turning (every 72 hours, give or take) to produce finished compost in as few as three weeks. Some gardeners feel that the sustained high-temperatures over 160°F kill off too many beneficial microbes and that there are fewer habitat zones and less biodiversity.
With these "single batch" systems, you'll need to store fresh material until the tumbler is ready for another load. Still, hot systems—especially when kept in direct sunlight—are perfect for gardeners who want to kill off weed seeds and quickly process garden-safe animal manure. They're also good "jump-starters" for inoculating larger, less active compost piles.
Choose a convenient spot for your composting system
Place your compost system where it's convenient for you. Keep it in a sunny area if you live in a cool summer climate, and the afternoon shade if you're in the Mojave desert. It's a good idea if you have easy access to a hose sprayer; when you're turning your pile, and it appears to be too dry, you can spray a bit of water into the mix. You want it moist, but not to the point at which you can squeeze drops out of it—the ideal moisture content is 50 to 60%.
- DO protect your compost system from rain. Soggy compost will smell, and the water will compact the materials.
- DO turn your compost every seven to 14 days. It will maintain consistent core temperature and allow outside material into the center.
- DO protect your compost system from bears, possums, rodents, and raccoons. Plant peppermint and oregano around your compost piles to discourage mice and rats.
- DO add a bit of aged or half-baked compost to new piles; this will inoculate the fresh material with essential beneficial microbes.
- DO chop up fresh materials whenever possible to hasten their decomposition.
- DON'T put diseased plants in your compost system. Burn or throw them away.
- DON'T compost meat, fat, or grease. There are separate systems for composting animal proteins and plant-based cholesterol products.
- DON'T compost pig, dog, and cat feces with compost intended for your garden. Same goes for human poop! Check out the Humanure Handbook by Joe Jenkins for practical advice on composting "dangerous" dookie.
Your garden will appreciate even the most basic composting strategy, and you might even find the process as enjoyable as your favorite gardening activities. Fresh compost always beats store-bought stuff!
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