This comprehensive guide to composting covers everything from bin construction to applying the finished product.
Truly sustainable fertility arises from the very land it nourishes. This compost was made from grass, leaves, crop residues, and kitchen garbage, all sourced from the farm itself.
Photo by Will Bonsall
With more than forty years of experience redefining gardening's boundaries, author Will Bonsall shows how readers can eliminate the use of off-farm inputs like fertilizers, minerals, and animal manures by practicing a purely veganic, or plant-based, agriculture-not for strictly moral or philosophical reasons, but because it is more ecologically efficient and makes good business sense.
In Will Bonsall’s Essential Guide to Radical, Self-Reliant Gardening, (Chelsea Green Publishing, 2015) he offers readers in-depth information on growing, harvesting, and processing an incredibly diverse variety of food crops. The following excerpt is from Chapter 1, “Composting as if it Mattered.”
You can purchase this book from the MOTHER EARTH NEWS STORE: Will Bonsall’s Essential Guide to Radical Self-Reliant Gardening.
I make compost and lots of it, and not just because it’s something hippie homesteaders are expected to do, but because I get a kick out of doing it. No, really. In my lifetime (so far, that is) I’ve made easily 200 tons (181 tonnes) of compost. (Well, not easily; it was a bodacious amount of work.) I still think it’s more fun than a barrel of monkeys to take a mess of useless stuff and turn it into a valuable product.
Compost is not my exclusive source of fertility; I also use green manures on some areas, and last year’s layer of decayed mulch is a significant source of nutrients; often it is enough by itself. However, the compost is a biggie, especially on certain heavy-feeding crops. It is crucial that I make enough compost and that the quality be good. And making good-quality compost requires more thought and effort than simply making a pile and letting compost happen.
I’ve known very few gardeners whose compost making furnishes most of their crops’ nutrient needs. (How far can grapefruit rinds and coffee grounds go toward building up the soil?) Typically, gardeners say that their compost is a source of humus, a source of trace minerals, or a bioactivator. They rely on hauled-in animal manure or purchased lime and other mined minerals to do the heavy lifting. This is where my garden-without-borders is different: My compost, in conjunction with green manure rotations and mulch, is intended to supply all the needs of my crops and the soil in which they live—the humus, the NPK, the good cooties, and so forth. And the ingredients in my compost all come from my immediate neighborhood. I do not bring in significant amounts of other stuff from afar. The main exception is leaves from the nearby town of Farmington, which I could as well collect from my own forest (and do), but theirs go to the landfill anyway, and I like to prevent that when I can.
Of course, many gardeners go beyond that and add their yard waste—leaves and grass clippings—which is a huge improvement. (You can see how nicely these things fit in with that eco-efficiency business I was talking about earlier.) Even so, typical compost systems are often wasteful and counterproductive. The ingredients consist largely of weeds, crop residues, and kitchen wastes whose nutrients arise from the garden or the marketplace. They get piled in a nondescript heap in a corner of the yard. There are no precise boundaries around the heap, so the stuff at the edges kind of moulders into the ground (a net loss to the garden system). Since stuff is added in dribs and drabs, the pile never really heats up. The weed seeds, the pest bug eggs, the disease spores are all concentrated there where they can ripen, hatch, or fester in rich luxuriance. Meanwhile the rains leach much of the goodness into the soil beneath the pile, the very place it is least needed. It puts me in mind of Julius Caesar: “The evil that men do lives after them, the good is oft interred with their bones.” What’s really aggravating about this is that most of that lost fertility originated in the garden.
To avoid loss of nutrients from compost, I take great pains to keep all the materials well contained within a series of bins consisting of upright posts and parallel planks and poles. There are five bins in my system, which requires 12 posts, each 10 feet (3.0 m) long, to construct. The posts are set apart 8 feet (2.4 m) on centers for the length of the bins, and 5 feet 4 inches (1.6 m) between the near surfaces of opposite pairs. Each pair is connected at the top by a spiked 2 × 4, which prevents the posts’ tendency to spread when the bins are filled.
The posts are sunk 3 feet (0.9 m) into the ground, so the frost doesn’t heave them about (if you live on Oahu, that last line might be lost on you). Now, digging a straight 3-foot vertical hole in Industry, Maine, is apt to involve as much quarrying as digging, so once I place those posts I’d appreciate it if I didn’t have to replace them for a while. I use cedar, which I hew with either a broadaxe or a chain saw to 5 × 5 inches (12.7 × 12.7 cm) by 10 feet (3 m) long. Cedar is rot-resistant, but not enough for me, so I scorch the bottom few feet in my sap furnace to a depth of 1⁄8 inch (3.2 mm). (Guess; you can’t measure it while aflame.) I do this because I know that bits of charcoal have been dug out of ruins thousands of years old, the rings just as clear as the day they were cut. It will not rot. Moreover, if the posts are green-cut or wet when I scorch them, the heated resins will form creosote, which is boiled into the interior—something like pressure-treated telephone poles.
When I set the posts I don’t fill around them with dirt. Instead I use small stones (if you have a shortage, bring over your pickup) tamped in firmly. The frost will not shift them in stone as much as it will shift them in dirt, and the risk of decay is further reduced if the underground portion is not in direct contact with moist soil. By the way I make sure the scorched part comes up at least to the surface, but not too much above, lest I blacken my clothes every time I rub past it. A reason why the posts are 10 feet (3.0 m) long is so they end up 7 feet (2.1 m) aboveground once they’re set. Thus the attached top crosspieces don’t get in my way, especially when I’m transferring stuff from one bin to the next.
The planks that form the back wall of each bin are spiked to the inside of the back-wall posts. When the bins are full the compost pushes the planks outward against the posts. The front-wall planking slides into slots, so I can remove any part of them for easier filling and emptying. I made the slots by nailing a 11⁄2 × 11⁄2-inch (3.8 × 3.8 cm) square onto the face side of the 5-inch (12.7 cm) wide beam, leaving a 2-inch (5.1 cm) gap between them. The planks that form the interior walls between bins also slide into slots. I use 2-inch cedar planks, which I mill with my chain saw. Add up the two layers of cedar planking and subtract them from the 5-foot, 4-inch (1.6 m) gap between posts, and that leaves an interior space 5 feet (1.5 m) wide.
By the way I don’t use plank siding on the front of the bins for the entire height of the pile. Above 3 feet (0.9 m) poles that are 2 to 4 inches (5.1–10.2 cm) in diameter serve just as well. I have acres of them and they’re easily prepared. When they become too decayed to serve the purpose, I simply put them through the chipper/shredder and they join the next bin (don’t get sentimental, we all return to the soil eventually). Why don’t I use poles for the whole thing? Kinsman Tom Vigue opines that their loose fit allows too much drying of the outer several inches of the heap and impedes its thorough heating, and I have come to agree with him in part (more on this topic later). The posts at each end of the system are also planked across to form the end walls, which helps prevent spreading, too.
Why did I choose 5 × 8 feet (1.5 × 2.4 m) as the inside dimensions of my bins? Mostly because of hearsay. I heard it said that a pile less than 4 feet (1.2 m) in any dimension would tend to dry out and not have enough critical mass to generate enough heat (I explain later why heat is so important). On the other hand at least one dimension should be less than 5 feet or else air would fail to penetrate the heap and it might become anaerobic (that’s Latin for “air failing to penetrate the heap,” and it’s not good). Okay, so that explains 5 feet wide, but why 8 feet long? I discovered, by measuring many batches of finished compost, that they all averaged around 50 pounds (22.7 kg) per cubic foot (0.03 cu m). That meant that a 5 × 8-foot bin—an area of 40 square feet (3.7 sq m)—would hold 1 ton (907 kg) for every foot (0.3 m) of depth. How convenient to calculate my supply at a glance! Moreover, there’s the matter of turning the pile with a compost fork: How far did I wish to fling that stuff? Experience suggested 8 feet for a maximum. If you cannot assemble enough material to fill such a large bin in a reasonable time, you can build it smaller, but no less than 4 × 4 × 4 feet (1.2 × 1.2 × 1.2 m) to ensure critical mass for proper heating.
My original system included a crude roof to shed excess rain, but it seemed those huge piles were always cooking themselves dry, at least in the early two stages—they needed more water, never less. When I eventually rebuilt the system, I didn’t bother to include roofs. Having said that, there might be a real advantage to some kind of protection in the finished stage, when there are more soluble nutrients and no heat is being generated. Someone suggested I use plastic tarps, which would also prevent blown dandelion or bird-dropped seeds from landing on the pile. Perhaps, but I’m trying to use less plastic (I call it ticky-tacky, from the classic Malvina Reynolds song), not more. Anyway, when my compost is finished I’m usually quick to spread it—organics aren’t meant to sit around.
So once it’s built what do I put into this system? The simple answer is: whatever I have and in whatever proportion I have it. Obviously not animal manure. Well, there will be plenty of worm poop and some droppings from the wild birds that eat them, but no domestic livestock manure. Since I’m not burdening myself or my land with domestic critters, why should I require it of others or their land? Anyway, I’m not big on moving lots of stuff around—eco-efficiency implies economy of energy as well as economical land use. Of course we are animals ourselves, and I certainly make use of our privy cleanings (night soil is the euphemism used by folks who don’t like to call something what it is), but I don’t use these in the general compost system I’m describing here.
I use all the usual crop residues and weeds from the garden; actually I’m embarrassed when weeds constitute a significant part of the pile, as it reflects poorly on my weed management ability. What I do appreciate about the weeds is the soil clinging to their roots, although I try to shake most of it off in the garden where it lives. A certain amount of soil in the pile is very desirable, much like the salt in a casserole, and since none of the other ingredients contain much of it, when I don’t have enough weeds I go dig up a few bucketfuls of dirt from the most organically sterile area I can find (it’s the minerals in the dirt I’m after; the rest of the pile is all about organic matter).
A visitor once commented with some hubris that she no longer wasted energy making compost; she just let everything rot where it lay in the garden. I didn’t venture to comment, as she clearly knew all she needed to know, but I continue to make compost nevertheless, thank you. Most of my compost material comes from outside the garden, and thus the compost I make provides a net gain in the garden’s fertility, not merely shuffling around what’s already there. But I should note, even that shuffling process is extremely important: Those old cabbage leaves and cornstalks, tomato vines and carrot tops, are often full of pest eggs, borers, blight spores, septoria, anthracnose, and so on, all of which may fester there on the soil surface, waiting to attack next year’s crop. Keep in mind that nearly all of our crop species are not native, and many of their pests are not found in the surrounding fields and forests, but only in our gardens. In a properly made compost heap, nearly all those pests and diseases will be destroyed by the heat generated by via aerobic fermentation (which does not occur in crop residues simply left lying in the garden), plus the myriad biologies that accompany accelerated decay.
The early stages of composting are totally dominated by thermophilic (heat-loving) bacteria, which cause most other bacteria, plus fungi and earthworms, to either leave the pile, go dormant, or die. Only after the pile cooks do the other decomposing agents go to work. Adding them to the pile before the fever has passed would be futile.
That being said, I don’t consider garden residues a mainstay of the heap—after all these plants are not very eco-efficient and their fertility arose from the garden in the first place. The heavy lifters in my pile, the stuff which brings fertility into the garden from outside, are the grass and tree leaves and ramial chips. Ramial chips is another name for small brush (under 3 inches, or 7.6 cm) which has been put through a chipper/shredder. It is distinct from trunk wood, which is mainly cellulose.
As I explained before these are the ingredients that make the overall system eco-efficient—make it work—since they build up long-term humus with a much smaller input of “earth-blessing” (space, nutrients, water, air, sunshine, et cetera). They do require something, of course—in particular, nitrogen.
Although I put all my garden residues and weeds through the compost system, that’s not always true of the grass and especially of the leaves and chips. As I said, they’re the mainstay of the heap—but I also use major quantities as mulch and in other ways (and that’s described later in the book).
Someone asked me once, in a theoretical vein I assume, whether I would use deer droppings in my compost piles if I chanced upon some in my woods. For one thing, since I’ve never known deer to poop in piles of any consequence, the time spent chasing around trying to gather it up would be much more profitably used mowing grass and shredding leaves. Moreover, I’m not sure how valuable a manure derived mainly from spruce and fir browse would be for cultivated crops. In fact the deer do occasionally loiter around my bins, nibbling on cider pomace that gets spilled there. If a deer were to inadvertently drop a few doe-berries in the pile, would I discard the whole batch as non-veganic? No, I think not.
Ideally I build a new compost pile every three or four weeks during the season (April through November), and one challenge is to have enough material at hand to build a complete 5 × 8 × 4-foot (1.5 × 2.4 × 1.2 m) pile within a few days so that it will heat up thoroughly and uniformly. Again, I’m counting on the heat generated by the pile to: kill pest eggs, destroy weed seeds, and cook any disease spores, plus commence the breakdown of fibrous materials. The materials in a compost heap built up over time do also break down—slow fungal activity would be the driving force—but without the initial bacterial fever, there would be too little heat to wipe out the baddies.
A second challenge is to have a reasonably consistent balance of ingredients. There’s plenty of leeway here, but I would prefer that the summer piles not be only grass, autumn only leaves, and spring only leftover kitchen garbage. Therefore I stockpile certain materials: hay, leaves, and kitchen garbage.
I put lots of fresh-cut grass directly into summer compost piles, but I make plenty into hay for autumn and spring piles. By “hay” I do not mean that I carefully cure and bale it for long storage as a dairyman does. Rather, I let it dry enough before raking so that it will not be fire-fanged and half rotten before I compost it. I would mention that my concept of “grass” or “hay” is much broader than a dairyman’s. When fed to big ungulates “grass” should be mainly grass with some succulent legumes, as in a timothy-clover mix. My bacteria and earthworms are not so finicky, so if my pasture contains oodles of buttercups and milkweed and goldenrod, so much the better, as long as it’s oodles. I want a dense yield of not-too-woody biomass; eco-efficiency is more sought after than digestibility.
Tree leaves especially tend to come all at once—October—so I try to collect them soon after they drop, shred them while crispy dry, and store them, mostly in a deep 8 × 10-foot (2.4 × 3.0 m) rain-proof bin, where I can access them at any time of year.
Likewise during the winter we generate many buckets of kitchen garbage, with no place to put it. The tight-lidded buckets accumulate outside until snow-go, at which time I can start the season’s first pile using this stored garbage, stored leaf shreds, and stored hay.
Now that we have an ingredients, list let’s consider how to build a pile. It’s important to keep in mind that the main direction fertility moves in a compost pile is down. There may be upward loss through volatilization, especially of ammonia compounds, but most nutrients are held in a water-based solution that is susceptible to gravity. This is even more true if we add enough water to keep the pile cooking—the biological fires are stoked, not quenched, by additional water. Therefore there is some risk that soluble goodies in the bottom layers may be leached into the soil beneath, and that’s about as helpful as a screen door in a submarine. I minimize this by starting a new pile with a few layers of highly absorbent, high-carbon materials, stuff that will actually benefit from the nitrogen-laden leachate from above. A typical sequence is ramial chips followed by spoil-hay (that’s the trashy stuff that was mown too late or let lie too long), then ramial chips again or shredded leaves, and again spoil-hay, repeated three times for a total of six bedding layers.
By the way, when I say a “layer” of hay, I’m thinking of a jumbo-sized wheelbarrow as full as I can pack it and pile it. When I say a “layer” of shredded leaves, I’m talking about that wheelbarrow filled to the brim and mounded, or about 25 or 30 gallons (94.6–113.6 l). The hay will pile higher than the leaves, but it will also settle more in the heap, so they’re probably roughly comparable. When I say a “layer” of kitchen garbage, I picture from two to four 5-gallon (18.9 l) bucketfuls.
Lacking spoil-hay I might simply alternate ramial with leaves, but I really prefer to alternate “forest stuff” with “pasture stuff.” In fact I like to follow that general pattern throughout the heap-building, as it better reflects the mutual role of those two ecosystems in feeding me. As a rule the forest stuff is high-carbon and will be acted upon slowly by fungal agents; the pasture stuff is higher in nitrogen, which fosters feverish bacterial growth. I’d hate to live in a world without either one; apparently my compost heap and the crops it nourishes feel the same way.
After the initial bedding layers I switch to something richer—maybe clover or comfrey or kitchen garbage—but henceforth I add whatever I have, trying to alternate wet/dry, nitrogen/carbon, mineral/organic. I want to end up with a pile as diverse and self-complementary as possible.
I should emphasize the importance of using a good proportion of dry trashy stuff to rich succulent matter, like at least three to one. The usual concern is that too much high-carbon material might moulder along without enough nitrogen (remember, that’s hearsay) to spark the bacterial heat. A reasonable concern, although a little nitrogen goes a long way, but people tend to ignore the opposite extreme: a high nitrogen-to-carbon ratio will make a pile heat up fine and in fact will drive off the surplus nitrogen in the form of ammonia and methane. That wastes fertility while filling up the atmosphere with ozone-destroying gases. People fret altogether too much about nitrogen in the soil and not enough about humus, just as they overrate protein in the diet while ignoring fiber. Either produces a toxemia of the system.
Despite the need for minerals in a compost pile, I never add lime (which I don’t have in my system anyway) or wood ash (though I have plenty of that). In the course of all its chemical permutations, the pile goes through both acidic and alkaline extremes, and I don’t wish to have such a strong base (alkali) interfere with any of that. Moreover I intend to use my compost on any and all crops, including some—like potatoes—that might take offence at the alkali.
As the pile grows, usually over a period of several days, I insert poles into the slotted front so I can heap it ever higher. If I sense that my ingredients are all on the dry side, I add a few bucketfuls of water as I go along, rather than relying on a massive soaking at the end, which may not penetrate evenly. I have usually not paid much attention to aerating the piles; indeed, in the first stage there is sometimes a concern about them being too fluffy with all that coarse dry stuff. But after watering the air pockets settle out and the heap becomes much denser. Too dense? Cousin Tom practices a variant of the traditional Indore method of composting. (The Indore method incorporates poles laid sideways across one or more layers. As a pile is built the poles are pulled out, leaving passageways for air.) Tom creates two or three “chimneys” into the core of a pile by bundling several sticks together (a bit of crookedness creates more air passageway; that’s good) and placing them upright as the pile builds. I’m uncertain whether it’s worth it: That new internal exposure allows moisture and heat to escape, whereas adequate oxygen has never seemed to be a problem for me. Still, Tom knows a good thing.
Eventually my heap reaches a height of 6 or 7 feet (1.8–2.1 m), and I can barely reach up to pile more stuff on. But the heap will soon shrink down to half that height, mainly due to air spaces settling out.
One last step before I call it complete: I fork a last extra-big layer of hay on top and dump on 50 gallons (189.2 l) of water. I used to haul that in buckets from a nearby pond, but now I have a hose from an irrigation tank on the hill, lazy me. Lastly, I cap it all off with a few bucketfuls of sifted (pebble-free) soil for weight and moisture retention and, of course, minerals.
Soon after I’ve finished the heap, then watered and capped it, it begins to heat up in a very big way. You probably know that putting damp hay bales into a hayloft can set the barn afire. The same process is at work in a compost pile, but since the heap is not tightly enclosed (as in a stuffy hayloft), the heat can dissipate without combusting. If a pile doesn’t heat up, the probable cause is lack of moisture. Without moisture the bacteria that generate the heat just can’t get started.
One year we had an apprentice who made a scientific study of our process: He bored a hole in the end of a 4-foot (1.2 m) 2 × 2-inch (5.1 × 5.1 cm) cedar square and inserted a cooking thermometer. Every morning he took an iron pry bar and bored a hole into the heap, inserting the thermometer into the centre. Using graph paper he kept a “fever chart” of every pile we made that summer. It was remarkable how similar the lines were, given the varied content and timing of each pile. The temperature of every pile spiked within the first three days, from ambient to 162°F (72.2°C), then slowly it would slide back to around 140°F (60.0°C) over a week or so, then it would plummet to something under 100°F (37.8°C). At that point (always on Day 19) it would nearly level off and presumably might take weeks to reach ambience, so great is the insulating power of compost.
From the data we concluded that Day 19 days was a good time to turn a heap into the next bin (usually we waited more like three weeks, to make sure). Turning the heap is important for several reasons, and I explain that below. It’s okay to wait longer than three weeks, but from the time a pile cools time’s a-wastin’, and we need that bin free to start another pile. For this reason I rarely start the first pile of the season in Bin #1 of my five bins. As soon as it is capped, I must wait 19 days for that bin to be freed up to start a new heap, and meanwhile grass and other ingredients are pouring in. If I start by building a pile at Bin #1, then for the next 19 days I am at a standstill, whereas if I start in Bin #2 or even #3 (out of five, remember), there is still room for everything to be turned at least twice. More important, as soon as the first pile (in #2, say) is built, I can immediately commence a new pile (in #1), delaying the holdup until perhaps there is a lull in the inflow of ingredients. This all may be of little concern to the backyard gardener who may be building only one heap for the whole season, but since I am typically generating between 12 and 20 tons (10.9 and 18.1 tonnes) of finished compost per year, I need to keep things moving. This is not a salad garden. Of course you can be much more casual about these matters when your food (and the fertility to produce it) comes from somewhere else.
To turn a pile I use a five-tined compost fork (I’m shocked to discover that my hardware store actually labels them thus, no longer as “manure forks”—a sign of who’s purchasing them?). It used to take me about 15 minutes to throw 1 ton (0.9 tonne) from one bin to the next, a forkful at a time. Now that I’m grown older it usually takes me a good 20 minutes or an hour for the whole heap. It’s not that I’m feebler; I just like to stop more often to contemplate how much fun I’m having.
There are several reasons for this turning, the main one being that the material on the top and sides of the heap was not wholly involved in the first round of heating to 162°F (72.2°C). The turning will incorporate all this stuff and there will be a second fever, though not as long or intense. However, that second heating is important to assure that everything is properly cooked. But is it indeed properly cooked? Cousin Tom has an interesting take on this: He thinks that covering the top and sides more tightly, to retain moisture and heat, would obviate the need for turning. Furthermore, he makes the excellent point that if the turning is supposed to leave the remaining ingredients cooked, it is of dubious value, since the secondary heating is definitely tamer and may be inadequate to kill some of the things we need killed. Whether or not that is true I have another compelling reason for turning: to create a more uniform product. Turning mixes all those layers while breaking up clumps of coarse junk so the agents of decay can better access it. That alone justifies the effort in my eyes.
If I turn a bin promptly every three weeks for a maximum of three times (or four stages), then the whole process takes twelve weeks, or less than three months, from beginning to end. Thus, a pile built in early June will be ready to apply in early September.
Three months from beginning to end does not of course mean that a pile commenced in late November will be finished in late February (except perhaps on Oahu). Obviously composting activity does not continue unabated through freezing weather, but neither does it come to a complete halt. I have commenced heaps in mid-December and had them seethe on into the New Year, melting the snow that fell on them to further water their interiors. This happens because even a bit of thawed stuff at the core will generate its mite of heat, which would be snuffed out by the surrounding chill were it not for the high insulating value of compost. Instead that little locus of living warmth thaws its surroundings a bit, generating yet a little more heat, and so forth until the whole heap is a steaming inferno. At some point, however, this process must succumb to the cold, at least where I live. Depending on the timing, this halt may come before the living heat can kindle; if a bunch of frozen materials are assembled in mid-January, it may be impossible for any microbial spark to catch, as even the bacteria drift into the suspended animation that is a northern winter. If the initial fermentation is able to begin and sustain itself through the first stage, once that cycle has cooled off, then it must fall into the icy grip of winter and be locked at that stage, even though there is lots more decaying to do.
Just as that insulating inertia keeps the pile cooking despite its bleak environs, that same inertia grasps the pile in its new permutation: a 3-ton (2.7 tonne) organic Popsicle. Nor will it hasten to relent, even when the sun is climbing and the robins are back. The ground has thawed enough so that plenty of earthworms are there for those robins, yet in the compost bins is a great gelid mass; it has made a contract with nature from which it is not easily released. If I’m in no rush, there’s no problem. But if I’m needing that bin free to build a new heap (yes, I’ve started piles in mid-April), or if that batch is finished and I want to apply it to early-spring beds, I speed things up by busting the stuff out with a maul or dull axe and spreading the chunks where I want them, where the sun and rain will thaw them much more quickly. Or I may scrape off the thawed layer on the top and sides, exposing the core to much quicker thawing. Otherwise I just wait.
Ultimately, whether sooner or later, despite your clever ploys and your stupid blunders, you will end up with compost. It’s really quite hard to prevent; it’s just a question of how long it takes and how valuable is the finished product.
So then, what do you do with it? The living community within it will continue feeding upon itself, mould becoming earthworms, centipedes becoming bacteria (and ultimately vice versa); life and death continue, decay marches on. Not, however, without a net loss of energy at each stage. If you added no fresh matter, I suppose the decomposition theoretically would result in ash, the mineral residue from which all the organic energy has been wrung out. For that reason if no other, compost should be put to work in the soil as soon as it reaches a finished condition (obviously it never reaches a finished condition—nor do we—but when the necessary biology has rendered it useful for cultivated plants). I call it finished when it is broken down into uniformly small particles that are unidentifiable.
An obvious way to use compost is to incorporate it into the soil shortly before sowing the crop that is to benefit from it. Further decomposition should occur in the soil, where the crop plant rootlets are prepared to take up the nutrients as they become available.
For example, if I start compost in June and it’s ready in early September, there is usually an open space where I’ve removed an early crop and another late crop is about to replace it. That’s a fine time and place to spread the new compost. But if that late-succession crop is to be a green manure, then the compost might be more prudently used elsewhere, or it might be spread in late fall for a spring crop. An advantage of this is that if the compost does contain some viable weed seeds, say due to inadequate heating, then they may sprout and get done in by late tilling or by winter. Again, I don’t like to have finished compost sitting around when it could be in or on the soil, powering a community of microbes whose services will be wanted anon.
My favorite way to incorporate compost is with a wheel hoe, using the crossbar or stirrup attachment, although the tines could also do a good job. This stirring in—as opposed to turning in (as with a plough)—has the advantage of keeping the organic matter in the top few inches, rather than burying it away from the life-giving air.
You can also use finished compost without incorporating it, but rather spreading it on the surface and letting earthworms and the rain incorporate it. An advantage of this is that it also serves as a mulch, protecting the soil surface from the elements. Of course, what then protects the compost from the elements? I believe it largely protects itself by trapping the nutrients until they can be moved downward (worms, rainwater, et cetera) and appropriated by crop plant roots. A possible disadvantage is that the more volatile nutrients (like ammonia) may evaporate, especially in direct sunlight. I usually avoid this by immediately adding a thin mulch of shredded leaves. Thus the first mulch is more for fertility; the second more for protection.
This double mulching is especially useful when I want to use unfinished compost: stuff that has been thoroughly heated by two cycles in the bins, yet still contains plenty of recognizable material. Of course many crops resent growing in such crude stuff—wouldn’t you?—but at least one crop loves it: tomatoes. Those semi-weeds revel at having their feet in near-garbage and will be disgustingly healthy, provided the compost contains no diseased tomato plants from last year. Another crop that seems to appreciate this rude treatment is squash, but not cukes or melons, which take themselves far too seriously. Ever notice which plants grow happily right in raw compost heaps? Certainly none that has any sense of decorum.
Take care if you decide to use finished compost to top-dress crops that are already up and growing. At best compost may spatter all over the plants to their detriment (lettuce and broccoli?—forget it); at worst, young plants may get buried or broken over.
I never make enough compost to adequately fertilize all my crops, but fortunately I don’t need to. Areas that were last in a green-manure rotation should need none, nor crops following a crop companion that included a living mulch. Most of mine goes on the intensively spaced veggie crops. When a legume is one of the companions, I use much less compost, relying on it more for humus than for specific nutrients. I’m far more generous with members of the cabbage family, which are over domesticated shallow-rooted crops requiring spoon-feeding—if only I didn’t love them so much.
Although I make all the compost I can, and of the best quality I can manage, I do not rely on that alone for my garden’s fertility. I also use green manures, mulches, and living mulches, and that’s the subject of the next chapter.
Reprinted with permission from Will Bonsall’s Essential Guide to Radical, Self-Reliant Gardening by Will Bonsall and published by Chelsea Green Publishing, 2015. Buy this book from our store: Will Bonsall’s Essential Guide to Radical, Self-Reliant Gardening.