How’s that compost coming?
If you live in a New York City apartment, it may be on hold, because the city has suspended its composting program (although there are workable alternatives). But if you’re lucky enough to have a garden of your own, there’s no time to lose.
“The answer to so many gardening questions is, typically, ‘compost,’” said Daryl Beyers, the author of “The New Gardener’s Handbook,” published this year. “Whether you’re adding it to help improve fertility or water-holding ability: Compost, compost, compost. Until people truly grasp the importance of building healthy soil, they will struggle in the garden.”
Encouraging new gardeners to foster healthy, productive soil — and to recycle kitchen and garden waste into compost, as the crux of that effort — is Mr. Beyers’s favorite part of the class on gardening fundamentals that he has been teaching at the New York Botanical Garden for 10 years.
Mr. Beyers, who preaches the virtues of soil science in his class and in the free Zoom question-and-answer sessions he has been holding on Mondays at 6:30 p.m., admits there is a certain irony in that. When he took the soil course in college, it didn’t go so well. “I did really badly, and almost failed,” he said. “And then it turned out to be the most important thing.”
He shared some basic composting advice, as well as his favorite system: pit composting, which doesn’t require buying or building anything, but rather digging a series of holes in the ground.
Lesson No. 1: Compost Is Not Fertilizer
It is decayed organic matter, or humus, that improves soil structure and promotes fertility when added to the garden. It does this by making nutrients and water more available to plants, while creating a living soil hospitable to all the essential organisms whose (mostly unseen) job is to recycle.
“Humus happens — composting is going on in every field and forest in the world,” Mr. Beyers said. “To support our garden soil, we just have to learn to mimic that process.”
The Recipe Is Simple, but a Little Confusing
In short: Mix green with browns, in roughly equal measure. Green is shorthand for nitrogen-rich materials like fresh grass clippings or the lettuce plants about to bolt. Brown represents those higher in carbon, like dried leaves or twiggy prunings.
Of course, it’s not always so obvious, Mr. Beyers acknowledged.
“One of most important lessons is to start to understand what’s a green and what’s a brown,” he said. “The way I explain it to my students: If you let it sit on your kitchen counter for a week, does it start to rot? It’s probably green. If it dries up, it’s brown.” (A list of ingredients.)
Don’t put all of the green — or a mass of any single ingredient — in one big lump. Layer it, and alternate. When Mr. Beyers adds a bowl of kitchen scraps, he tosses a handful or two of shredded paper on top, and then a sprinkling of soil.
You’ll know the balance is wrong if compost isn’t happening fast enough. Then try adding green. But if there is a funky odor or you see flies, add brown.
Animals may take an interest in a compost pile. A shovelful of soil and some dry leaves or shredded paper on top of food waste is a deterrent, and tumblers (see below) are the most animal-proof device.
Don’t Include Everything
Any organic — in other words, living or formerly living — material can be composted, but some of those materials should be left out of home systems.
Don’t add meat, dairy, eggs or oily foods. Composted manures from herbivorous farm animals like chickens or cows are welcome; those of carnivorous domestic pets are not. Eggshells and fish bones are neither green nor brown, but they are mineral-rich and can be added.
Mr. Beyers does not add diseased plants or weeds with rhizomes that might re-sprout. “I do compost weeds with seeds,” he said, “because the heat of the process makes the seeds unviable.”
He also composts uncoated black-and-white paper, like newsprint, junk mail or computer paper, and corrugated cardboard (all considered browns), shredding or tearing it up first.
Coffee grounds — a popular additive among kitchen wastes — are doubly confusing. They’re brown in color and don’t decay if left sitting out, but are actually a green, rich in nitrogen. As Mr. Beyers said, it takes a little homework.
Any material will break down faster if it’s added in smaller pieces. A whole tomato vine will eventually break down, but cut up first, it moves along faster.
Other Key Ingredients
Air and just enough moisture are also essential to get microbes working. Sunshine provides the heat.
Site your composting setup “in a place that’s not superhot and sunny, but also not dank and shady,” Mr. Beyers said. During periods of little or no rain, moisten the compost slightly with the hose.
Don’t Be Fooled Into Buying Compost Starter
“Inoculate your pile or bin for free with an occasional shovelful of garden soil, loaded with the microbes that do the work,” Mr. Beyers said. “Later, use some of your finished compost.”
Different Gardens (and Gardeners) Need Different Systems
The tumbler suits urban gardens, or those with limited space. The downside: You can’t just keep adding fresh material, or you will never get to harvest anything.
“You add material and tumble, and add more and tumble, but you don’t harvest until you’ve been tumbling a full unit for a few weeks, with no more additions,” said Mr. Beyers, who recommends a dual tumbler, or two tumblers. “You fill one up, start tumbling, and then start filling the second.”
Closed bins, also called composters, are another small-garden option. But don’t put a bin or a tumbler in all-day sun or the heat buildup will harm the microbes.
Open bins, made of wire, wood slats, pallets, concrete blocks or straw bales, are often set up as three compartments, allowing several stages of decomposition. Turning each periodically speeds breakdown. The downside: Unless you’re using concrete blocks, you will have to rebuild every few years.
Don’t Want to Look at the Pile or Use a Bin?
Then compost in a pit. Mr. Beyers started pit composting as a renter, worried his landlord would object to a heap of debris visible to neighbors.
Then he thought, “Why don’t I just dig a hole?’” he recalled. “And it ended up working so well that I’ve re-created it at my own home.”
Choose a spot where three pits or trenches of equal size can be dug alongside one another. Start with one, perhaps four by four feet, and two feet deep. Pile excavated soil beside the first pit. Begin adding wastes, like kitchen scraps, dry leaves and soil, then fresh weeds, shredded paper and soil, and so on.
“I continue every time: green, brown, soil; green, brown, soil,” Mr. Beyers said.
Start a second pit when the material in the first is about a foot above ground.
The average process in Mr. Beyers’s Northeast backyard: “If I start Pit 1 in April, and it’s full by July, I dig Pit 2,” he said. He fills that until about September, but more material is still to come, and Pit 1 isn’t ready yet. “So I dig Pit 3. I fill Pit 3 throughout the winter, and by spring, Pit 3 is full, I harvest Pit 1 and start filling it again. And so on.”
The method isn’t as fast as a pile you turn or a tumbler, but it can be made smaller or larger as needs change, and it isn’t an eyesore.
“Plus, the soil that you dug out is a whole pile of compost starter,” Mr. Beyers said.
The Laziest Way of All
Pile things up in an open heap — or, more passively still, do sheet composting or sheet mulching. In recent years, sheet composting has become known as lasagna gardening, but it’s an old technique, modeled on the way trees’ leaves drop and degrade slowly into the soil. Simply place the compostable material in existing or new beds — again, alternating greens and browns.
The Payoff: Using Your Finished Compost
Unless you have a very big garden and a very big system, demand for compost will exceed supply.
“I’m very particular about who gets the compost,” Mr. Beyers said, as even his three-pit system doesn’t yield enough homemade stuff. “I’ll top-dress my vegetable plants, my dahlias and other flowers, spreading an inch thick around the root zone of each.”
He happily harvests whenever finished material is ready. “It could be spring, which is great,” he said. “But it could be July, and I put it on then, too, focusing on problem areas, where I want to improve soil over time.”
Pit composting, step by step:
In spring, dig the first pit, maybe four by four feet, and two feet deep, in a spot where there is room for two similar pits alongside it. Pile the excavated soil to the side to use as inoculant.
Step 2: As raw material is produced, add it in alternating green and brown layers, with a sprinkling of soil each time. Shredded paper — recycled household or office waste — is a great “brown” ingredient.
Step 3: From summer into fall, when the contents of the first pit are a foot above soil level, start a second pit alongside it. Keep adding materials according to the green-brown soil recipe.
Step 4: In fall or early winter, dig a third pit that will carry you through to spring. This time, add the excavated soil on top of the middle pit. Keep filling in the second until its contents are a foot above grade. The first pit should be ready for harvest in spring, and then can be used again for incoming debris.
The reward: Finished compost, of which gardeners can never have enough. Layer an inch or so onto root zones of key plants, or spread in areas where the soil needs improving.