Cultivating Questions Concerning the Bio-Extensive Market Garden
by Anne and Eric Nordell of Trout Run, PA
In the Winter CQ we described our longtime practice of mulching strawberries, medicinal herbs, and other short term perennials with wheat straw overwinter. For the past half dozen years, we have also used a heavy mulch of straw in the valleys of our minimum-till ridge planting system for long term EARLY planted vegetables, such as onions and garlic. More recently, we have begun mulching LATE planted vegetables, like fall broccoli and kale, established during the hottest and driest part of the growing season. A light mulch of straw in the pathways goes a long way toward preserving moisture from the increasingly sporadic summer rains.
For the same reason, we decided last year to mulch winter squash, a long term crop that does not tolerate moisture stress. However, for these sprawling cucurbits, we attempted to grow-our-own mulch rather than buying in more wheat straw. Even at the reasonable price of $2.25/bale delivered; mulching almost a third of our vegetables has become a significant expense for our low budget operation, undermining our original goal of relying on the internal resources of the farm as much as possible.
The photos document our trial run with on-farm production of rye mulch in 2007. On April 11, we applied half a spreader load (approximately one yard) of compost right down the middle of a fallow field where rye and red clover had been seeded September 16, 2006. We followed the spreader with the two-way riding plow, skim plowing the 12’ wide strip shown in the top photo.
We plowed early and shallow to prevent the over wintering cover crop from pulling the winter accumulation of precipitation out of the soil, to hold that moisture as close to the surface as possible, and to allow a 6-8 week period of additional moisture collection before planting the squash. Although killing the cover crop prematurely sacrifices a good bit of biomass production, this moisture preserving strategy turned out to be a crop save in ’07 which turned dry in our area the middle of May. We received only one soaking rain from then until the second week of August.
The second photo, taken on July 3, shows the three varieties of squash (delicata, butternut, and kabocha) direct seeded on May 28 and protected with floating row cover and a heavy mulch of rye straw. The warmer temperature under the row cover accelerates germination and growth of the squash in our cool climate. More importantly, the cover serves as a physical barrier to cucumber beetles which can transmit bacterial wilt to the squash. Removing the cover when the first squash blossoms appear is necessary for pollination.
As for the fallow year management of the cover crop on either side of the squash, we mowed the rye for the first time on May 9, creating a light mulch of 2’ long residue for the clover underneath. The second mowing took place on June 13 when the rye regrowth reached 3-4’ tall and full pollen drop. We knew from past experience that clipping the rye at this stage of maturity maximizes its biomass production without danger of producing viable seed.
We let the rye clippings dry for a few days before raking the long straw into a 4-6” deep mulch on either side of the row covered squash. It required a 20’ wide section of second-cut rye to produce mulch 4’ wide – roughly a 5:1 ratio. (In another fallow field where we repeated the experiment with a summer planting of zucchini, a 3:1 ratio was sufficient, but in this case we mowed the rye only once, on May 22, and raked all of the 4 ½-5’ tall biomass next to the zukes.)
As you can see in photos 3 and 4, the winter squash seemed to thrive despite the dry, and at times, very hot weather. Although the vines showed some heat stress, they never wilted. By contrast, the red clover, which was 8-12” tall at the time of the second clipping of rye, looked parched all summer long, reviving only after we received 5” of rain in August. We mowed the stressed clover every 4 weeks to prevent the prolific blossoms from going to seed.
The last photo was taken during the squash harvest on September 15. We were impressed with the number, size and quality of the fruit, a major improvement over our yields in similarly dry years. We grossed approximately $1400 from the 380’ row, more than enough to cover the taxes, opportunity cost (land rent) and management expenses of this half-acre fallow field plus a small profit.
Growing-our-own mulch turned out to be a convenient and economical way to improve un-irrigated squash production and offset the costs of taking land out of production. And we were able to take advantage of this moisture saving system without completely derailing the soil building objectives of the fallow year. The bulk of the fallow field benefited from a full year cover crop of rye and red clover, with the first clipping of rye and several later clippings of clover returned to the soil. The 12’ wide strip of squash in the center of the fallow field received compost plus the second cutting of rye. In addition, we seeded this strip down to rye right after the squash harvest.
The only thing missing was our usual bare fallow period for weed control. In this field it was hardly necessary as evidenced by the lack of weeds in the un-mulched middle of the squash row despite the use of weed stimulating row cover and no cultivating or hand hoeing. If we had tried this experiment during our first years on the farm, we would have spent many hours hand weeding the squash to reduce crop competition and to prevent the weeds from going to seed.
We have set aside two fallow fields for repeating the squash experiment in 2008. This time we plan on including our usual summer fallow treatment to see if we can grow-our-own mulch and realize this weed depleting aspect of the fallow year management.
If we are successful, the next challenge will be somehow adapting this homegrown mulch method to the short term perennials, ridge planted alliums, and fall brassicas. Assuming a ratio of 3-5 acres of mulch-producing cover crops for every acre of vegetables, a super-extensive market garden might be required to realize this new goal for sustainable moisture control.
Doubling or tripling our land base may not be justifiable, especially when we remember that mulching is not the foundation of our dryland system for growing produce without irrigation, just the latest addition. To help put our use of straw mulch in perspective, we conclude this column with an article we put together for the Spring 2007 Natural Farmer, outlining in a step-by-step fashion our approach to moisture management.
MARKET FARMING AFTER PEAK WATER
Peak Oil sounded the alarm that in just a matter of years half of the easily extracted oil in the world will be consumed. We can’t help thinking that Peak Water should become the rallying cry of the new millennium as well. After all, half of the readily available potable water across much of the globe has already been used or polluted.
Agriculture has suffered as a result of this dwindling resource, especially in areas dependent on pumping fossil water. At the same time, farming has been a major contributor to Peak Water. Irrigation represents the lion share of the rapid increase in world-wide water consumption.
With an average annual precipitation of 42” here in north-central Pennsylvania, we can hardly complain about lack of moisture. In fact, when we moved to the area in 1982, the neighboring dairy farmers assured us there would be plenty of rainfall for growing vegetables. Not realizing the big difference in moisture requirements between field crops and produce, we naively decided against digging a well and purchasing irrigation equipment. Instead, we focused on preserving soil moisture.
For the past 25 growing seasons, we have used the dryland practices described in this article to direct seed and transplant vegetables all season long without irrigation. Of course, rainfall has been necessary to finish out some of our longer term crops, and yields have generally been better in wet weather. Nevertheless, we consistently get good stands of produce without precipitation or watering in the plants, and our income from dryland fruits and vegetables has increased every year without expanding acreage.
Although not a substitute for irrigation, the following moisture preserving ideas may possibly be helpful to growers making do with limited access to water or simply desiring to reduce the size of their hydrological footprint.
Like most organic growers, we try to maintain a respectable percentage of organic matter in the soil. Good levels of humus are particularly important for dryland market farming because organic matter acts like a sponge in the soil, absorbing excess moisture and holding it until the crops need it.
We maintain soil organic matter by taking half of the market garden out of production each year just to grow soil building cover crops. Although it may not be realistic to expect large increases in organic matter from cover crops alone, our experience suggests that growing two mature annual cover crops in the fallow year following each cash crop can offset most of the organic matter loss associated with intensively cultivated vegetables.
At least, regular soil testing indicates that the organic matter in the market garden averages 3.5% despite routine use of bare fallow periods and pre-plant tillage for weed control. By comparison, the adjacent permanent pasture, which has not been tilled in over 30 years, tests just one-half per cent higher in organic matter than the vegetable fields.
We can increase the moisture holding capacity of the land by making sure that water moves freely between the topsoil and subsoil. Deep tillage is often used for this purpose to improve infiltration and drainage. On heavier clay soils this sort of mechanical manipulation may be necessary. However, the improvement in moisture movement may be short lived. Intensive, deep tillage can also be counterproductive if it destroys the natural crumb structure or creates large clods and air spaces that impede capillary action.
Instead of using deep tillage to improve soil structure, we rely on the extensive root system of the fallow year cover crops to aggregate the siltloam topsoil and open up the red clay subsoil. Conditioning the land with cover crops allows the rainfall to go deep in to the earth – and to return to the surface as the soil dries out.
THE SIX WEEK RULE
Taking half of the market garden out of production each year makes it possible to realize the full soil structuring potential of the cover crops well ahead of planting the vegetables. This is important because the cover crops can remove a lot of moisture from the soil during their peak vegetative growth. In fact the ground may be bone dry by the time the cover crops have produced the bulk of their above and below ground biomass.
For this reason, we make a point of killing the cover crops at least six weeks before planting the vegetables. Call us lucky, but so far we have been able to count on at least one moisture restoring rain during this six week period. In the future, it may be necessary to extend this moisture collection period to 8 or 10 weeks to compensate for the increasing extremes in the weather.
Killing the cover crops does not necessarily require intensive, soil drying tillage. For example, crimping, mowing, or shallowly undercutting the cover crop in early bloom is usually sufficient to kill the cover crop and prevent it from taking more moisture out of the ground. We use these noninvasive techniques to kill a cover crop of rye and hairy vetch the third or fourth week of May, six weeks before planting the first of the fall vegetables in the middle of July.
Killing cover crops at least six weeks before planting spring vegetables is even easier. We simply use frost sensitive covers that naturally die back over winter. Winter-killed cover crops, such as oats and Canadian field peas, or sorghum-sudangrass and forage soybeans, guarantee a dead root system and cover crop mulch well before spring arrives, in this way conserving the whole winter store of moisture. Our goal is to establish these cold sensitive covers the first part of August in order to maximize their top-growth and root system before the onset of winter at our Zone 5 location.
We limit tillage to the top 2-3” of the soil for three moisture related reasons. First, it only takes a week or two of hot, windy weather to dry the soil to tillage depth on our exposed, hilltop site. Consequently, we till only as deeply as necessary to form an adequate seedbed for planting and cultivating.
Second, restricting the depth of tillage keeps the soil structure developed by the cover crops’ root system intact, insuring that the subsoil moisture can wick up to the root zone of the vegetables via capillary action. Maintaining soil structure with surface tillage also allows the roots of the vegetables to grow quickly and deeply in search of water.
Third, working the earth shallowly concentrates the cover crop residues in the top two inches of the soil. The resulting cover crop mulch prevents the moisture moving up from the subsoil from reaching the soil surface and evaporating.
Shallow tillage also stops capillary action from releasing moisture to the atmosphere by creating a mulch of loose, dry soil. In our experience, the combination of a cover crop mulch and an earth mulch is much more effective at holding in moisture than relying on just one or the other of these moisture conserving practices.
We often compress the cover crop-earth mulch with a cultipacker to hold moisture within a half inch of the soil surface for planting vegetables. The disadvantage to firming the soil surface in this manner is reduced infiltration of rain and increased runoff. Recently, we have discovered that following the roller with a rotary hoe, or some other form of light tillage, seems to markedly improve infiltration while holding moisture close enough to the soil surface to direct seed and transplant market garden crops all season long without irrigation.
To transplant vegetables without irrigation, we use a one-inch wide shovel on the cultivator to mark a narrow planting furrow. We set the starts in this slit in the soil, making sure to firm their roots into the moist earth and to reestablish the dry mulch of soil and cover crop residues around the base of the plants. Using this simple method, we do not need to water in the plants, and we cannot remember ever losing a plug or bare-rooted start to transplant shock.
Direct seeding vegetables without irrigation is not as straightforward. During long stretches of hot, windy weather, it is often necessary to move the dry layer of cover crop-earth mulch out of the planting zone before shallowly planting small seeded crops, like carrots, spinach and salad mix.
One way we do this is to imitate the lister planting techniques developed in the arid parts of the U.S. We use a middlebuster-style furrower on the cultivator to move the dry mulch materials to the sides of the planting row. In the process, this extra-wide sweep exposes a narrow band of moist residue-free soil ideal for trouble-free seeding with the walk-behind Planet Jr.
One drawback to lister planting is that the crop ends up below ground level, making cultivation much more of a challenge. To minimize this problem, we like to establish the winterkilled cover crops on ridges. Moving the dry cover crop-earth mulch off the top of the ridges with the furrower results in a 10-12” wide band of clean, moist soil an inch or two above ground level. With either method of dryland direct seeding, some sort of crop protection, such as rolling or hanging shields, may be necessary to prevent burying slow growing vegetables with soil and cover crop residues during cultivation.
After planting the produce, we rely on the cultivator to maintain a moisture conserving earth mulch during the first critical weeks of crop establishment. The idea is to get in to the fields with the cultivator after each packing rain to loosen the sealed soil and reestablish the mulch of loose earth around the young plants. Not coincidentally, timing cultivation to follow shortly after each significant rainfall does a good job of weed control as well as moisture preservation.
Depending on the crop and the soil temperature, we stop cultivating to preserve soil moisture 2-6 weeks after planting the vegetables and turn our attention to creating more permanent forms of ground cover. In the case of long-term, high value produce, we think it is worth the time and expense to apply a thick mulch of straw between the crop rows. We may use as much as 4-5 tons of clean wheat straw per acre to provide full season moisture retention.
For short-term or low value vegetables, we find it more economical to apply a much lighter mulch of straw in the pathways. As little as one to two tons per acre is adequate to minimize runoff and partially shade the soil. Regardless of the depth of the mulch, we make sure not to place the straw close to the plants in order to maintain good air circulation and to guarantee that even the lightest of showers reaches the soil in the root zone of the vegetables.
Although not as effective at holding in moisture, we use living mulches to provide soil cover for most of our crops because planting the living mulches involves so much less labor and expense compared to applying straw mulch by hand. In some cases the living mulches provide additional services, like fixing nitrogen, attracting/distracting insects, and alleviating compaction in the pathways.
Our favorite living mulch is hairy vetch, seeded in a single row down the middle of the between-row area. This single-row interseeding system concentrates the vetch roots in the center of the pathways well away from the crop, in this way preventing the vetch from competing directly with the vegetables for either nutrients or moisture. At the same time, the prostrate vetch vines slowly-but-surely form a ground hugging mat, providing sufficient soil cover within 4-6 weeks of interseeding to shade the pathways and minimize runoff.
If the carpet of vetch threatens to climb up on top of the crop, then we simply attach coulters or disc hillers to the cultivator to trim back the vetch vines on either side of the row. Using the cultivator for this unusual purpose is a whole lot easier and faster than mowing living mulches between the vegetables.
LOW WEED PRESSURE
Good weed management is essential to insure the vegetables get the full benefit of all the preserved rainfall. Low weed pressure is also necessary for implementing many of the practices we use to conserve moisture. For example, utilizing shallow tillage and cultivation to create cover crop-earth mulches would not be possible if perennial weeds were a major problem. Likewise, high numbers of annual broadleaf weeds would rule out the economical use of living mulches or light applications of straw to provide ground cover.
Keep in mind that the six week moisture collection period between killing the cover crop and planting the vegetables opens up a window of opportunity to use shallow tillage to germinate and kill a generation or two of annual weeds before the produce goes in the ground. We also use this stale seedbed technique between cover crops in the fallow years. As a result, most of our fields are now virtually weed-free.
Low weed pressure, in turn, has made it possible to develop what we think is the ultimate minimum-till system for managing moisture in both wet and dry conditions. We begin in August of the fallow year by planting a winterkilled cover crop of oats on the ridges. Early the next spring, we plant the vegetables directly into the dead cover crop mulch on the ridgetops, adding enough wheat straw in the valleys for full season moisture retention.
For vegetables planted later in the spring or early summer, we lightly till the ridgetops with the rotary hoe to prevent the ridges from getting hard and drying out. Loosening the ridgetops also enhances soil warming and aeration while facilitating direct seeding and transplanting.
Based on five years’ experience with very extreme weather, we think this minimum-till ridge planting system provides the vegetables with the best of both worlds: a warm and well-drained root zone on the ridgetops during cold, wet weather; and a large reserve of soil moisture under the mulch in the valleys for the crops to draw on when conditions turn hot and dry.
Perhaps our most controversial moisture conserving practice is planting all of the vegetables we grow in single rows 32” apart. However, in our situation, moisture is a more limiting resource than land, so it makes sense for us to provide every crop, even small canopied vegetables like cutting lettuce and spinach, with a large reservoir of soil moisture. The payoff is we can grow heads of leaf lettuce to market size without rainfall or irrigation as long as the temperature does not get too extreme.
Planting all the crops at the same row spacing also simplifies cultivation so we can quickly and efficiently cultivate the whole market garden after a packing rain to slow down evaporation. In addition, widely spaced rows makes it much easier to cultivate tender vegetables surrounded by lots of cover crop trash, to apply straw mulches by hand in the pathways, and to take advantage of the minimum-till ridge planting system.
Many of our reasons for using single rows would be negated if the cover crops were chopped into small pieces with a flail mower and then rotovated shallowly into the soil. This simple change in the mechanics of field management should make it possible to plant and cultivate vegetables in multiple-row beds and still conserve enough surface moisture for good crop establishment despite long periods of dry weather. Where irrigation is an option, this combination of multiple-row plantings and dryland practices might represent the most efficient and sustainable use of both natural and man-made water.
MULCHING FALL VEGETABLES
Mulching fall vegetables with clean wheat straw the second week of August. The dryland practices described in this article made it possible to transplant and direct seed the alternating rows of brassicas, spinach, beets, beans and salad mix during an extended dry period in July. The mulch in the pathways preserved an abundance of late summer rains so these fall crops could really thrive during the unusually mild and dry weather the last half of September and October.
A rate of 120 lbs. of wheat straw per 380’ pathway (roughly 2 ½ tons to the acre) provided more than adequate ground cover to prevent runoff and slow down evaporation from the generous rainfall we received the latter part of August and beginning of September. Note that we do not apply the mulch next to the row, leaving at least a 12” band of open soil to insure that even the lightest of showers moisten the root zone of the vegetables while they are getting established and to maintain good air circulation when they reach maturity.
Alternating the rows between long term, large canopied brassicas and low growing, short-term crops like lettuce, spinach and salad mix, facilitates harvest and plays a role in moisture management. By the time the short term crops have been harvested, the roots of broccoli, collards and kale have already extended into these beds in search of moisture and nutrients. For this wide diversity of crops, we have found a straw mulch in the pathways provides better moisture retention and soil protection through the fall and over winter than our usual single row interseeding of rye or hairy vetch.
MINIMUM-TILL RIDGE PLANTING SYSTEM
A heavy blanket of winterkilled oats and field peas holding in the winter accumulation of moisture. Planted on August 15, 2005, this mix of Leonard oats (3 bu/acre) and Maxum peas (60 lbs/acre) produced over two tons of dry biomass by November as determined by Cornell researcher, Meagan Cocke.
Chopping cover crop trash on the ridgetops with the residue cutter in April. Note the sliding hitch on the forecart has been offset for the second pass to cut the residues into small pieces.
Following the residue cutter with this old pull-type rotary hoe does a beautiful job of lightly tilling the ridgetops while popping out small weeds. The ridges give this cultivating tool more purchase, turning the rotary hoe into a primary tillage implement.
Two or three passes with the rotary hoe, going in opposite directions, creates an ideal cover crop-earth mulch for preserving moisture and…
…sheds a lot of the cover crop trash into the valleys, enhancing soil warming on the ridgetops, reducing runoff in the valleys and facilitating direct seeding and transplanting. Note the moist, crumbly soil for hand setting bare-rooted onions the third week of May without irrigation in the dry year of 2006.
For long term moisture preservation, we apply straw mulch to the valleys, as much as 4-5 tons/acre.
Curing onions on the ridges in a field with poor drainage in 2004. On a couple of occasions we received so much rain there was standing water in the valleys while these onions were getting established. Then it turned hot and dry right when the onions started to bulb up and moisture demand was the greatest. Judging from the size and health of the crop, the minimum-till ridges provide a well-drained root zone for the crop while maintaining a large reservoir of moisture under the mulch.