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Cultivating Questions High-Value Cover Cropping

Cultivating Questions

Concerning the Bio-Extensive Market Garden

by Anne and Eric Nordell of Trout Run, PA

Getting Started on Limited Acres with High-Value Cover Cropping

Our winter workshops seem to generate a lot of interest in bioextensive market gardening among young growers. However, we sense an undercurrent of frustration because many of the participants do not have access to enough land to fallow half of the market garden. We hope that the following list of speculative suggestions will provide some encouragement to new vegetable farmers who cannot afford to take land out of production but want to take advantage of the bioextensive principles of rotational cover cropping, minimum-depth tillage, and bare fallowing.

1. Stale seed bedding before or after each cash crop can serve the same purpose as the bare fallow periods we use to reduce the weed seed bank in the soil. If the production schedule does not allow enough time for regular stale seed bedding with a propane flamer or very light cultivation, consider using a quick succession of short term cultivated vegetables to flush weeds out of the soil as recommended in Crop Rotation On Organic Farms, edited by Chuck Mohler and Sue Ellen Johnson.

Weed control is often difficult in crops like onion and carrot because they are slow growing and cast relatively little shade. Although some weeds establish from the long-term seed bank in the soil, many of the weeds encountered in a given year establish from seeds shed in the previous year or two. Consequently, growing a crop in which weed seed production can be prevented before planting a poor competitor can reduce the amount of precision cultivation and hand weeding required for successful production of the poor competitor. Cropping strategies in which management prevents weed seed production include successive plantings of short-season crops, short-cycle cover crops alternating with clean fallow periods, crops grown with weed-suppressive mulch, and highly competitive crops that are intensively cultivated (for example, potato)….

One expert farmer uses intensively cultivated crops to control bad weed infestations. For example, infestations of bindweed and Canada thistle are followed by a triple crop of lettuce, which is high value enough to justify the costs of frequent cultivation. This is followed by a weed-suppressing cover crop of rye.

Crop Rotation on Organic Farms by Chuck Mohler and Sue Ellen Johnson

2. A limited land base also need not interfere with the practice of using shallow tillage to fiberize the seedbed and prevent bringing new weed seeds up to the surface. If time is of the essence, shredding the cover crops or crop residues into small pieces with a flail mower before shallow rototilling should significantly speed up decomposition and seedbed preparation compared to our horsedrawn minimum-depth tillage techniques. Where hand tools are employed, removing the crop residues from the field for composting may be necessary to facilitate tilling just the top two to three inches of the soil.

3. Research at Cornell and the University of Maine has shown that it is possible to produce as much, or even more, cover crop biomass when growing a cash crop every year as our every-other-year fallow system. The key is using a high percentage of early harvested and late planted vegetables in the rotation to open up large windows for cover cropping. Following early harvested vegetables with late planted crops the next year not only maximizes cover crop potential but also helps to reduce weed pressure by preventing different families of weeds from repeatedly going to seed.

4. If land and time constraints rule out cover cropping altogether, consider using the cash crops as cover crops and vice-versa. This suggestion may sound like a case of having your cover crop and eating it, too, but it is based on the experience of three innovative growers who made use of high-value cover crops for generating income, rebuilding soil structure and reducing weed pressure.

For many years Eero Ruutilla has routinely taken land out of production on his Nesenkeag Farm in New Hampshire to reduce weed competition for the following year’s direct seeded vegetables. During this fallow year, he grows two oat-and-pea cover crops back-to-back, intentionally letting the spring planting go to seed before tilling it in so that it will self-seed the second planting late summer. Not only does the first planting of oats and forage peas produce free cover crop seed, it also grosses over $30,000 a year in pea tendrils sold to upscale restaurants.

At the 2009 Great Plains Vegetable Conference, Klaus Karbaumer described to us his innovative solution for cover cropping in a land-limited situation. He broadcasts the seed of high-value vegetables, such as mustard, turnips and cutting lettuce, over portions of the market garden that need soil protection and weed suppression. His marketable cover crops shade out troublesome grasses, enhance soil tilth, and increase sales for the two-acre Missouri market garden. We asked Klaus to write up the details of this profitable cover cropping system for this column.

To the best of our knowledge, Eliot Coleman’s New Organic Grower provided the first comprehensive model for maximizing cover crop potential in an annual vegetable system. In this organic farming classic, Eliot describes the eight year rotation he used in Vermont to grow a vegetable crop and a cover crop every year by establishing small grain green manures immediately after early harvested vegetables or undersowing the long-term, late harvested crops with different types of clovers. Later, when he moved to Maine and began developing his year round production system, Eliot rotated mobile greenhouses to allow a full year of clover to build up the soil before a twelve month succession of vegetables grown under protection – perhaps the ultimate combination of bio-extensive and intensive practices.

So you can imagine our surprise when reading his new The Winter Harvest Handbook (Chelsea Green 2009) to find out that Eliot Coleman and Barbara Damrosch have dispensed with cover cropping altogether in order to keep up with growing demand for their superior, “deep organic” produce. This is the most attractive and enlightening book on sustainable vegetable production we have seen, and page after page of Barbara’s stunning photos of their densely-planted patchwork of non-stop produce convinced us that they have not given up on cover cropping, but taken it to the next level by practicing almost continuous cover cropping with vegetables. Their rapid succession of intensively seeded high-value cash crops provides few opportunities for weeds to get established or go to seed and protects the soil with live vegetation and a dense root system virtually year round.

Eliot and Barbara’s Four Seasons Farm illustrates so well that the time tested practices of rotation, cover cropping, shallow tillage and stale seed bedding can be adapted to very intensive, land-limited production. In our minds, the choice between growing intensively or extensively is not so much a question of which method is most biologically efficient or effective, but a practical consequence of the farm’s most limited resources.

For example, Eliot concludes the chapter on “Marketing and Economics” by noting that after many years of research and development they now gross an incredible $80,000/acre from the 1-1/2 acres they have reclaimed from the rocky, impoverished pine woods land. Including the quarter-acre in greenhouses, producing as many as six cash crops in a twelve month period, they average four crops a year across the 1-1/2 acre land base. Each intensive planting grosses, on average, $20,000/acre.

By comparison, our gross income from the 6-1/2 acre bio-extensive market garden is only $75,000. That’s just over $24,000/acre for the three dryland acres single-cropped in 34″ rows each year plus the approximately 3300 square feet of intensively planted and irrigated portahoopies and herb beds in the house gardens. Including the fallow lands, gross income per acre drops below $12,000. Clearly, an intensive approach to market gardening, as exemplified by Four Season Farm, would make the most economic sense if land is the limited factor.

However, if labor is the most limited resource, intensive may not always be better. The Winter Harvest Handbook indicates that Barbara and Eliot hire five employees in the summer, fewer in the winter. The actual size of the work force is difficult to determine because, as Barbara explained over the phone, “it has been a moving target,” changing with their goals for the farm, time devoted to research and writing projects, and the mix of winter crops (requiring more labor) and summer crops (which they are focusing on now). Assuming the equivalent of three to five full-time workers covers the range of labor scenarios in recent years, Four Season Farm grosses somewhere between $24,000 and $40,000 per person.

Beech Grove Farm is artificially labor-limited by our quality-of-life goal of keeping the farm a two-person operation. In reality, it has morphed into a two-and-a-half person operation over the years if we take into account the friends and neighbors we now hire on a part-time basis to keep up with work in the packing shed and demand at the farmers market. Our return on labor is $30,000 per person.

Compost is also a somewhat arbitrarily limited resource on our farm since we decided to limit our compost-making capacity to the manure generated by our four work horses. We can get away with just four tons of compost per acre per crop because we grow our vegetables in widely spaced rows and devote a whole year to soil building cover crops before each cash corp. From the unusual viewpoint of return-on-soil inputs, each ton of compost generates over $5,000 in gross sales.

Continuous, intensive vegetable production, on the other hand, often requires higher fertility inputs. At Four Seasons Farm, Eliot applies 15 tons of compost/acre per crop to insure high yields of quality produce and to maintain “potting mix quality” planting conditions so essential to managing dense seedings. Each ton of compost grosses under $1500.

We fear that this economic comparison between two farms at either end of the intensive-extensive spectrum may be very misleading due to a whole host of variables, such as markets, prices, soils and climate. These factors may have a greater influence on the gross return per acre, per person and per ton of compost than the method of production. Nevertheless, the experience of many beginning farmers we know support the comparison and highlight why it is so important to design the market garden with the most limiting resources of the farm in mind.

We have met new growers who have tried to implement our bio-extensive system and finally had to give up for several, different resource-related reasons: they simply could not generate enough income when taking half of their limited land base out of production; they had enough acres available for bioextensive management but not all the land was suitable for vegetable production – when they rotated the produce into the poorer, less well-drained parts of the farm crop yields and quality suffered; they had access to enough prime vegetable land for bio-extensive market gardening, but did not possess the appropriate tools or power source for managing all the acres in a timely and efficient manner. All of these farmers achieved greater financial success and personal satisfaction by intensifying production on fewer acres.

By the same token, we have gotten to know beginning growers, who, for purely philosophical reasons, chose to utilize just a small portion of their land base for very intensive production. Not only did they greatly underestimate the labor requirements, but crop quality and size was not satisfactory to establish thriving markets until they intensified fertility inputs and extensified production over more acres.

We trust readers realize that designing the market garden with the farm’s most limiting resources in mind does not have to be an either/or proposition. In many cases, a combination of intensive and extensive practices may be the ideal solution during the first years on the farm. Likewise, the mix of intensive and extensive management may change over time.

If, starting out, building soil fertility is the most pressing issue, it may be a good idea to follow Eliot Coleman’s example, during the early years in Maine, of alternating intensive vegetable production with twelve months of clover. Then, as the soil improves and markets develop, the shift to continuous, intensive production may be possible.

If weeds are the primary challenge, it might be better to divide the production area into two separate sections as described in the Spring, 2007 CQ on “Bio-Extensive Weed Management for the Land-Limited Market Gardener.” The one part could be devoted to an annual vegetable/cover cropping system a la Eliot’s 8-year Vermont rotation. Only vegetables that are naturally weed competitive or easy to cultivate would go in this area.

Less weed competitive crops would be slated for the second section where our every-other-year fallow system would be implemented to reduce weed pressure. The savings in labor for hand weeding should justify taking half of this section out of production. Over time, it may be possible to double and triple-crop the section dedicated to bio-extensive management and to take advantage of high-value cover cropping in the fallow lands.

Cultivating Questions High-Value Cover Cropping

Excerpts and photos from Eliot Coleman’s The Winter Harvest Handbook, photos by Barbara Damrosch


“If farmed intensively, a small area of land can be very productive. The key to increased productivity is to make better year-round use of every square foot. The most impressive skill of the old Parisian growers was their ability to develop techniques for maximizing output from their one- to two-acre holdings. When looking to expand production on our own farm, given our limited land base, we refer to finding the “hidden farm.” Whenever a section of our land is empty of crops and something could have been growing there, that is the hidden farm.

“In our quest to find the hidden farm, the intensity of our cropping has reached the point where we grow almost no green manures anymore because we are growing commercial crops so early and late. Yes, we lose the organic matter contribution from a green manure, but we gain the organic matter contribution from the root residues, outer leaves and stems of the harvested crop in addition to the financial return from selling it. We double-crop and triple-crop most of our outdoor fields. We also sow at much closer in-row and between-row spacing than used by large-scale field growers. Not only do we sow twelve rows of baby leaf salads and radishes or carrots on a 30-inch (75 cm) bed in the greenhouses, we use that same close spacing in the field.”

Cultivating Questions High-Value Cover Cropping


“We spread a layer of our well-finished compost on the soil before each succession crop at the rate of one 5-gallon bucket to each 10 feet of 30-inch-wide bed. If you weigh it out, that comes to a rate of about 15 tons per acre. Since we plant and harvest at least four succession crops per bed in an average year, our yearly compost application works out to about 60 tons per year. Although that is a lot less than the 100 to 400 tons used by the Parisian growers, it might seem high to some readers. If we had access to unlimited horse manure supplies as the Parisian growers did we would probably use more ourselves. Soil organic matter, whether from composted manure or composted vegetable wastes, is what powers this system. Intensive growing and intensive harvesting means intensive maintenance of soil fertility. You need high fertility for high production.”

Cultivating Questions High-Value Cover Cropping


“We wanted a well-designed electric tiller for greenhouse use, but since I could not find one I designed one myself and convinced a local manufacturer to produce it. We name it the “Tilther” since it is designed to work only the top 2 inches of the soil. I decided on 2 inches based on weed research indicating that weed seeds rarely germinate from more than 2 inches deep in the soil. Shallow soil working has always seemed desirable so as not to disturb soil structure, and the 2-inch depth made sense because it would avoid disturbing those dormant weed seeds that were unlikely to germinate as long as we did not move them closer to the soil surface.”

Cultivating Questions High-Value Cover Cropping


“It is always a better idea to prevent weeds rather than confront them. So our first approach is to see that no weed ever goes to seed. We hand-weed in the fields and greenhouses whenever necessary. We have even hand-weeded green manures to prevent weeds from producing seed, or tilled the green manure under and started again when there were too many weeds. Studies have shown that the serious weed-seed load in a soil can be greatly reduced over three to five years if no new seeds are introduced. However, even under the best of conditions weeds will appear.

“Given that reality, our second approach is to dispatch the weeds after they germinate but before the crop appears. The best way to accomplish that goal is with pre-emergence flaming, which means using a propane flame to kill the weed seedlings on a seeded area just before the crop emerges. The not-yet-emerged crop seeds are insulated from the heat of the flame by the soil. Timing is the key. In practice we like to prepare the area up to two weeks, if possible, before the sowing date, but any length of time is helpful. We will irrigate the area during the pre-sowing time, if necessary, to ensure weed-seed germination. We seed that area without further cultivating, wait the ideal number of days, and then flame off the small weeds. This is especially important for the crops planted in rows 2-1/4 inches apart for which we have never found a cultivating tool that works well.”

– Eliot Coleman, The Winter Harvest Handbook, published by Chelsea Green, 2009

Cultivating Questions High-Value Cover Cropping