The Slowcook at Spydog Farm The Slowcook at Spydog Farm

Profiles in Fertility: Maintaining Garden Soil Organically

March 15th, 2010 · 3 Comments · Posted in garden, Sustainability, urban agriculture

Shredding leaves for compost

Shredding leaves for compost

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 from a 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 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.”

El, who gardens in Michigan, described her solution:

“Moving to the country AND getting animals.  At first, I was gathering our pine needles until I realized there was poison ivy growing nearby, then I gathered bagged leaves from curbsides in town, then I asked a neighbor who had horses (and they gladly dumped pickup truck loads for me) and THEN we got the bagger for the lawn tractor.  Then, we got enough animals to make a difference. 

“Sigh. It’s all a process, and I am still of the belief that one can never have enough compost or mulch…temporary surpluses, maybe, but not enough.

“I’m testing that theory though with the goats’ output.  Pee is much more highly activating than dried chicken poop.  But!  It takes me almost two hours to haul out the goat shed, and that’s about 30 to 40 wheelbarrowloads of (mostly) straw.  And:  I do this monthly.  Yikes!

“I have raised beds into which I regularly add about a foot or more of compost and mulch every year.  (Compost:  mostly used chicken/goat straw bedding, kitchen/garden scraps, and–it’s true–all unusable guts/feathers/feet/heads of the poultry.  Mulch:  grass/leaf clippings the garden tractor picks up.)

“Other (more minor) practices:  I plant potatoes, tomatoes/peppers, squash seeds and onion-y things directly into compost in their holes, hills or trenches.  Everything else doesn’t need it nearly as much; in fact, root crops (carrots, etc.) and the cole family tend to hate super-nitrogenated soils of the composted variety so they don’t get anything.  And the squash is the only plant I baby with compost tea.”

Reader Luci Wilson offered this:

“Well, I’m kind of spoiled because I also keep a small flock of chickens and a handful of dairy goats, so I sheet mulch the straw bedding mixed with poop and ammonia from the goat pen on top of my (vegetable) beds each fall.  That way in spring it’s already partially composted, the winter rains have worked the nutrients into the soil and everything is already mulched.  I just have to lay in the drip lines and drop my plants and seeds into the planting holes.

“I do compost the chicken manure and use it sparingly around the landscape.”
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.”

And reader Amy described this system designed for a farm in Utah:

“We’re just starting to farm an eight-parcel piece of land. We are doing a few passive solar greenhouses and a lot of open field.

“Our plan is use a bit of new technology and combine it with Old World know-how. The new technology is greenhouse plastic. The particular plastic we use creates diffused light so that low-growing plants (green manure cover crops) can thrive when planted between tall growing plants like our tomatoes and peppers.

“The green manure (legume cover crops) fix nitrogen on their roots. The plan is to allow them to grow, then come through with a sod cutter to kill the plant. The plant has to die for the nitrogen to be released into the soil.

“We’ll be doing this both inside our greenhouses and in the field crops.

“When we rotate the crops we’ll plant where the cover crop has been growing and grow cover crop where the plants have been growing.”

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.



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  • Sylvie

    Ed – thanks for doing that. It’s great reading everybody’s practices. Alchemy indeed. But if the garden is continually doing well, then you’ve reach an equilibrium. SO much the better indeed if we could get all the stuff we need “on-farm”. I forgot… I also use chicken manure, now that we have chicken, in the compost pile.

    so… are you next doing a post on humanure? That’s where my husband draws the line. sigh…

  • Diane

    I attended a humanure talk last summer at the NOFA conference and the topic of Chinese farmers and human waste came up. The speaker pointed out that they don’t eat salads. In other words, if you grow vegetables with uncomposted, unaged human waste it MUST be cooked. Humanure is safe if treated properly for the requisite length of time but I would prefer to apply it to non-food areas of the garden.

  • Ed Bruske

    “The Humanure Handbook” is one of the best books on composting I know. It should be required reading for all gardeners. Or maybe for anyone who eats.