By Ed Bruske
For 4,000 years prior to the advent of factory-made fertilizers, the Chinese used every bit of organic matter they could lay their hands on–including their own excrement–to return to the soil the nitrogen and other nutrients their vegetable crops removed. It was only through meticulous attention to the cycle of terrestrial rot upon which new life depends that Asian cultures managed to cultivate the same land intensively for centuries, and thereby sustain themselves.
Americans have never been quite so industrious. In colonial days, raising livestock and growing vegetables went hand-in-hand–but not always. Farmers who applied manure and cover crops to maintain fertility were called “improvers.” Other farmers, citing a shortage of labor for soil husbandry, simply tilled their land until the soil was exhausted of nutrients. They then moved to greener pastures, something the western frontier seemed to offer in infinite abundance.
Today the frontier is long gone and modern “improvers”–otherwise known as organic gardeners–are left to ponder where to get the materials they need to maintain soil fertility. I should know. I go to great lengths to make the compost I use to feed my hungry kitchen garden here in the District of Columbia: snatching leaves my neighbors put at the curb in the fall; begging grass clippings from landscaping crews; hauling bags of coffee grounds from Starbucks; shoveling buckets of horse manure froma riding stables; religiously collecting our own kitchen scraps. Yet, it never seems to be enough.
My guess is that most urban and suburban gardeners operate at a soil deficit, meaning they don’t generate enough compost or manure of their own to adequately fertilize their soil. Unlike the Chinese, our culture treats the organic matter we should be putting back into the soil as waste material, shipping it off to landfills or flushing it down the toilet. Thus, while we disdain industrially produced fertilizers and pesticides, organic gardeners remain largely dependent on fossil-fueled modern commerce to provide the soil amendments our crops require, be it compost, horse manure or fish emulsion. What’s more, there is no agreement on specific practices when it comes to deciding what amendments–or cover crops–to use and how much.
I recently asked readers of my personal blog, The Slow Cook, as well as garden blogger friends and subscribers to the D.C. Urban Gardeners listserv, how they approach the question of maintaining soil fertility. Specifically, what do you use to improve your soil, and how much? As you can see from their responses, there is a wide diversity of approaches. In fact, organic gardening remains a kind of home-grown alchemy for which there seem to be as many different formulae for success as there are practitioners.
Among the most precise responses was this one from Joshua Wenz, who operates a professional vegetable gardening service. He also is a partner in the Neighborhood Farm Initiative, which grows produce for sale on a plot near Ft. Totten NE and teaches neophytes how to garden.
“To replenish soil fertility in my gardens and my clients’ gardens,” Joshua wrote, “I use:
“Compost (an inch or so a year)
“Nitrogen (N): Alfalfa meal, sometimes (but rarely) chicken manure. Twelve pounds, or about 36 cups per 100 sq feet per year. Easy to find on-line, but I haven’t found it locally, which is where the chicken manure comes in handy
“Phosphorous (P): Colloidal Phosphate. FEDCO sells “Tennessee Brown” which is essentially gleaned from phosphate mining tailings. Purportedly has less heavy metals, and of course is recycled. Hard rock phosphate is all I’ve found locally. Colloidal phosphate seems to be preferred by organic growers to hard rock phosphate, but I can’t seem to find anything that outright shows one is more sustainable or environmentally friendly than the other. Amount added depends on soil analysis and I only add every three years.
“Potassium (K): Greensand, or sometimes wood ash if pH is low enough. Available locally. Amount added depends on soil analysis, and also once every three years.
“For trace nutrients, kelp meal, azomite, other rock dust would probably work. I do that every three years as well.”
On the subject of cover-cropping, or planting sacrificial crops that act as fertilizer, Joshua had this to say:
“Cover cropping is a bear. It requires following a strict schedule on when to mow
and till. You won’t be able to work it in by hand. I have tried vetch/cowpea/oats
mixes, ryegrass, clover in raised garden beds with loose fluffy soil and it was
too tough to cut and work into the soil without a tiller. I now just pull it up
and use it as a mulch or toss into the compost.
“Buckwheat’s easier, but done in six to eight weeks, and make sure to mow or till when you don’t want it to reseed anymore.”
D.C. gardener Patrick Polischuk, who maintains four garden beds, each six feet long and two to three feet wide, offered this:
“Compost. How much? As much as I can. Two to three inches at planting and if I have enough, another surface application part-way through a crop’s season…I make the compost in two big bins out of yard scraps, kitchen scraps, and most of my block’s fall leaves.”
Christa Carignan, who gardens behind her home in Rockville, Maryland, said this:
“I use homemade compost made from leaves and kitchen scraps, but unfortunately I never have quite enough to feed all five of my veggie beds sufficiently each spring/fall. I have two compost bins (one cubic yard each) and I am lucky if I get enough mature compost to put about one inch on all the beds once each year. Not enough.
“Last year I got a truckload of mushroom compost from Pennsylvania (only $25 for a pickup truck full + the kindness of family members to deliver it here). I added about three to four inches of mushroom compost last spring and it really gave my garden a good boost. I will do the same again this year.”
Sylvie Rowand, who gardens in Rappahannock County, Virginia, had this to say:
“Compost, compost and more compost.
“I compost everything I can get my hands on. You could say I grow grass so I can make compost. When I used to live in the city, I would get several truckloads of shredded leaves from the city every winter, the grass clippings of neighbors who did not spray their lawn, coffee grounds from the office, and we’d take regular trips to Rock Creek stables (for manure).
“Today, I have grass fields, lots of garden debris, horse manure, straw, leaves – and as I say, whatever I can get my hand on. My best beds have four to six inches of compost on top. Actually my best beds used to be my compost piles. I have huge compost piles, and they change locations every year. When one is done, I just spread it a little and plant straight in. Now that the garden is reaching its physical limits – at least for a few years – I can focus on making compost to retop all the beds.”
Pattie Baker, who gardens behind her home outside Atlanta, Georgia, favors a complex scheme of cover cropping in her vegetable beds:
“I find gardening pretty hard and labor intensive—our red clay is such poor quality so it really takes a lot of time, effort and money to coax anything out of this land. My yields are never what I’d call bountiful. Perhaps we as a society have done so much damage and lost so much topsoil that we will never be able to replenish our soil enough. And not having enough on-site animal manure for continual renewal is a societal problem.
“I make sure every bed gets some cover crop action at some point every year. This doesn’t have to be the whole bed—sometimes it’s one edge of the bed, as with buckwheat or oats. As for sorghum, I usually plant a row of them along a fence or something as an edge, where it’s not going to interfere with veggies too much . For instance I have one small bed that’s very wet where I have mostly black-eyed susans, daisies and mint. I usually put a row of sorghum or Hungarian broom corn on the fence line in that bed, which I usually leave standing through the winter as birds eat the seeds and like to perch on the tall stalks. I usually throw a few seeds in other beds as well, and then grow beans up the stalks in late summer.
“With crimson clover (here we plant that in the fall and it grows all winter, flowering in May) and cowpeas (a summer legume cover crop), I usually do the whole bed and then till it in at various stages—the majority of the bed will get tilled in after just a few weeks of growth (then you let it sit for two weeks for the microbial action to do its job, then you either remove the debris to your compost pile, if you are planting seeds, or you plant directly into it, if you are planting transplants). With hairy vetch (which is an absolute lady bug magnet!), I pull it out and add it to the compost pile or let it decompose on the bed. I usually leave a small patch here and there of any cover crop I grow to flower and attract pollinators. Here is my BIG SECRET: rabbits don’t touch a THING if they have crimson clover to nibble on. They LOVE it. It grows like mad and they eat it like mad, so I make sure that I have some all over the place. Crimson clover and hairy vetch keep coming back, by the way, so you plant it once and then just manage it year after year, letting it grow here, digging it in there, adding it to the compost pile from over there.
“Fun crimson clover fact: It is relatively EASY for kids to find four-leaf clovers in a nice-sized crimson clover patch. (Keeps ‘em busy for a little while, too J)
“So, in short, here is the plan:
“Crimson clover and hairy vetch—plant in the fall (not sure if you can plant it now, but probably can) in any bed where you want to boost fertility for the summer crop.
“Sorghum, oats or rye (not winter rye grass), Hungarian broom corn—plant with first summer planting.
“Cowpeas, buckwheat—plant mid-summer for a couple weeks to boost fertility for second summer planting (you may not have a second planting like that in your climate) or to boost fertility for fall planting.
“Some people swear by winter rye, but I do find that one hard to pull up or till in by hand, so I’ve been avoiding it.
“The thing most folks don’t know about cover crops? They are BEAUTIFUL. They add height and movement and color to the garden. And they attract so many other living things. I now find a vegetable garden without them to be almost barren.
“Cover crops are also terrific for starting new beds.
“Do I sacrifice growing space for cover crops? Gladly.”
Eliot Coleman, the Maine production gardener and author, says that a one-inch application of compost is “very generous.” Coleman writes that once soil fertility is established, “a maintenance application of 1/4 to 1/2 inch per year should be more than enough to maintain and improve your garden’s productivity.”
Meanwhile, The Rodale Book of Composting advises applying “1/2 inch to 3 inches of well-finished compost over your garden each year,” preferably about a month before planting. Spring is ideal.
As you can see, even Eliot Coleman and Rodale do not agree. Me, I suppose I follow the Eliot Coleman approach. I work about 1/4 inch of compost into the soil in spring, then apply a little more with each new planting. My compost is made with ground leaves and straw, kitchen scraps, coffee grounds from Starbucks and horse manure. I have never been able to make enough, but I’m getting closer each year. I have lots of beds to cover.
Ed Bruske writes The S low Cook blog.
[Cross-posted from the DC Food for All.]
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