Using a spade, remove the soil from a trench 1 foot deep and 1 foot wide across the width of the bed, and put the soil into buckets or a wheelbarrow for use in making compost and flat soil. If the bed is 5 feet wide, the soil will fill 7 5-gallon buckets. (The trench is being dug across the width of the bed.)
Sides of bed may be dug outward into path.
Sides of bed may be dug outward into path.
The goal of double-digging is to loosen the soil to a depth of 24 inches below the surface. The first year, you may only be able to reach 15 to 18 inches with reasonable effort. Be satisfied with this result. Do not strain yourself or your tools. More important than perfection the first year or two is going in the right direction. Nature, the loose soil, worms, and the plant roots will further loosen the soil with each crop so digging will be easier each year and the depth will increase 3 to 6 inches annually.
For all-around ease, D-handled flat spades and D-handled spading forks of good temper are usually used for bed preparation. (Poor tools will wear out rapidly while you are preparing your garden area.) D-handles allow you to stand straight with the tool directly in front of you. You must frequently hold a long-handled tool to your side. This position does not allow for simple, direct posture and leverage. When digging for long periods of time, many people find the use of a D-handled tool less tiring (though it will probably take the digging of 3 beds to
get used to!). However, people with back problems may need long-handled tools. In fact, people with back problems and those not in good health should check with their physician before proceeding with the physically active process of double-digging.
The flat spade has a particular advantage in that it digs equally deep all along its edge rather than in a pointed v pattern. This is especially important in the double-dig since all points in the bed should be dug to an equal depth. The blade on the flat spade also goes into the soil at less of an angle and without the usual shovel's curve. This means the sides of the bed can be dug perpendicular or even diagonally outward into the path, a plus for root penetration and water flow.
You should only dig when the soil is evenly moist. It is easier and also better for the soil. Digging a hard, dry soil breaks down the structure, and it is difficult to penetrate. wet soil is heavy and easily compacted. Compaction destroys friable structure and minimizes aeration. These conditions kill microbiotic life. The main reason for drying-out periods after watering the
3b(i). For compacted soil: While standing in the trench, loosen the soil an additional 12 inches with a spading fork by digging in the tool to its full depth and lifting out a tight soil section on the fork pan.
3b(ii). Then, by moving your arms upward in a small jerk, the soil will break apart as it falls downward, hits the fork tines, and falls into the hole below.
soil is to attain the proper moisture level and to make digging enjoyable and beneficial. Soil is too dry for digging when it is loose and will not hold its shape after being squeezed in the palm of your hand (in the cases of sands or loams) or when it is hard and dry and cannot be penetrated by a spade (in the case of clays). Soil is too wet when it sticks to the spade as you dig.
Double-digging is the term used for the process of preparing your soil 2 spades deep (about 24 inches). To begin, mark out a bed 3 to 5 feet wide and at least 3 feet long. Most people prefer a bed 5, 10, or 20 feet long, but the maximum is up to you. To double-dig, remove the soil from a trench 1 foot deep and 1 foot wide across the width of one end of the bed. Use a 5/8-inch-thick plywood board, 2 to 3 feet long by 3 to 5 feet wide, to stand on. Place it on top of the 1-inch compost layer you spread over your bed, and advance it along the bed 1 foot at a time as you prepare to dig each new trench. Move 7 5-gallon buckets of soil from the beginning of the bed to a soil storage area for use in making compost and flat soil.
You can move the soil with the spade, in buckets, or by wheelbarrow. Make as few motions and use as little muscle as possible in this process. This will conserve your energy and involve less work. In fact, as you dig the soil, you will discover you can use an Aikido-like economy of motion and energy in which you are virtually just shifting your balance and weight rather than digging. (For a visual representation of this, see the Dig It! video carried by Ecology Action's Bountiful Gardens international mail-order service.)
Now, standing in the trench, dig down another 12 inches (if possible) with a spading fork, a few inches at a time if the soil is tight. Leave the fork as deep as it has penetrated, and loosen the subsoil by pushing the fork handle down and levering the tines through the soil. If the soil is not loose enough for this process, lift the chunk of soil out of the trench on the fork tines. Then throw the chunk slightly upward, and allow it to fall back on the tines so it will break apart. If this does not work, use the points of the fork tines to break the soil apart. Work from one end of the trench to the other in this manner.
Next, dig another trench behind the first one, moving each spadeful of the top 12 inches of soil forward into the first trench. Sometimes you will have to work over a trench a second or third time to remove all the soil and obtain the proper trench size. Repeat the subsoil loosening process in the second trench. Dig a third trench, and so on, until the entire bed has been double-dug. (When you are through double-digging, the aerated soil in the bed will be enough to fill in the last trench at the end of the bed, and you will have added some soil to the bed in the form of cured compost.) It helps to level the soil with a rake after every 3 to 4 trenches during the digging process.
When you are sliding the soil forward from one trench into another, notice two things. First, some of the compost layer you have added to the surface of the bed before beginning to dig slides 3 to 6 inches down into the trench creating a small mound of soil or landslide. This approximates the way nature adds leaves, flower bodies, and other decaying vegetation to the top of the soil, where they break down and their essences percolate into the soil. Second, the upper layer of soil—the top 12 inches—should not be turned over during the double-dig and succeeding double-digs. Most of the microbiotic life lives in the upper 6 inches of the soil. Also, the natural layering of the soil that is caused by rainfall and leaching, leaf litter, temperature, gravity, and other natural forces is less disturbed when the soil is not generally mixed, even though the soil is loosened up and disturbed somewhat. Aim for a balance between nature's natural stratification and the loosened landsliding soil. (As a goal, strive not to mix the soil layers. The goal is important even though it will never be reached and significant mixing sometimes occurs. Without this goal, however, excessive disruption of the soil layers will occur.)
TYPES OF DEEP SOIL PREPARATION
Ecology Action uses four basic types of deep soil preparation processes: the initial double-dig, the ongoing double-dig, the complete texturizing double-dig, and the U-bar dig. Following are simplified side views of each of these processes. The first two are described in the text.
The complete texturizing double-dig was developed to improve soil quality more rapidly and is used one time only. It is used usually in place of the initial double-dig, but it can be used
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at a later point in time. We have found this soil preparation process greatly improves plant health and yields immediately in poor, compacted and heavy soil. It is often worth the extra digging time involved. However, it does use an insustainable amount of organic matter.
The U-bar dig can be used as a substitute for the ongoing double-dig in soil that is in reasonably good shape. This usually means after one normal double-dig or more. The 18-inch-long U-bar tines (see page 13) do not prepare the soil as deeply as a spade and a spading fork used to double-dig 24 inches deep, but the lower 12 inches of the growing bed compact more slowly over time than the upper 12 inches. Also, the U-bar appears to have the advantage of mixing up the soil strata much less than double-digging with a spade and a spading fork. It aerates the soil less, however. This is an advantage in looser, sandier soil and can be a problem in tighter clays. If you use a U-bar regularly, do a normal double-dig as often as increased compaction
A primary difference between the ongoing and the initial double-dig is that the compost is put on after the digging process in the ongoing double-dig.
After the lower trench has been loosened, potatoes may be placed on its surface on 9-inch centers using offset spacing (see "Seed Propagation," pages 63-65). The soil from the next trench's upper level may then be moved forward onto them. This is the easiest way we have found to plant potatoes. (Mark the location of the potatoes with stones or sticks in the outside paths before covering them with soil. This will indicate where potatoes should be placed on the surface of each succeeding lower trench.)
12 inches deep.
See Backyard Homestead, Mini-Farm and Garden Log Book on the proper techniques for using a U-bar.
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Once the bed is prepared, you will truly appreciate its width. The distance between the tips of your fingers and your nose is about 3 feet when your arm is extended out to the side. Thus a 3- to 5-foot-wide bed can be fertilized, planted, weeded, and harvested from each side with relative ease, and insects can be controlled without walking on the bed. A 3- to 5-foot width also allows a good miniclimate to develop under closely spaced plants. You may wish to use a narrower bed, 11/2 to 21/2 feet wide, for plants supported by stakes, such as tomatoes, pole beans, and pole peas, for easier harvesting.
Try not to step on the growing beds once they have been prepared. To do so compacts the soil and makes it more difficult for the plants to grow. If the bed must be walked on, use the double-digging board. This will displace your weight over a large area and minimize the damage. Plants obtain much of their water and nutrients through the contact of their root hairs with the soil. If they do not develop an abundant supply of root hairs, less water and nutrients are taken in. The root hairs are more numerous and vigorous in looser soil, so keep your soil loose.
When weeding, note that the entire weed root usually comes up out of loosened raised-bed soil. This is a welcome change to weeding, and, if you get all the root, you will not have to weed as often. Also, you do not need to cultivate the soil of raised beds as much as other gardens. The living mulch shade cover provided by mature plants helps to keep the soil surface loose. If the soil compacts between young plants before the mini-climate takes effect, you should cultivate.
Soil in the path is subject to compaction; soil in the bed remains loose.
Soil in the path is subject to compaction; soil in the bed remains loose.
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Once this beautifully alive bed is prepared, it should be kept evenly moist until and after planting so the microbiotic life and plants will stay alive. The bed should be planted as soon as possible so the plants can take advantage of the new surge of life made possible by bringing together the soil, compost, air, water, sun, and fertilizers.
A good growing bed will often be 2 to 10 inches higher than the soil's original surface. A good soil contains 50% air space. (In fact, adequate air is one of the missing ingredients in most soil preparation processes.) Increased air space allows for increased diffusion of oxygen (which the roots and microbes depend on) into the soil, and of carbon dioxide (which the leaves depend on) out of the soil. The increased "breathing" ability of a double-dug bed is a key to improved plant health. Thus, the prepared depth will be as much as 34 inches in clayey soil. A sandy soil will probably not raise as high as clayey soil at first.
If the bed raises higher than 10 inches as you are double-digging, be sure to level it out with a rake as you go along. Otherwise you will end up with a very wide and deep trench at the end of the bed. Then you will have to move a large amount of soil from one end of the bed to the other to even it out when you are tired. This would also cause a disproportionate misplacing of topsoil into the subsoil area. Whenever you re-dig a bed (after each crop or season), the 24-inch depth of the bed should be measured from the top of the bed, rather than from the path surface. We currently reprepare the soil after each
For different types of ongoing soil cultivation practices to use after digging, refer to the "Cultivation" information sheet in the Gardening Techniques information packet (see page 228).
crop, except for autumn compost crops. Some people prefer to do this only once each year. As your soil improves and the large clods disappear, your bed may not raise as high as initially. Do not worry about this. It is just a sign that you and your soil are successful. The goal of double-digging is not the height of the bed, but the looseness and good structure of the soil.
Once a good structure has been established by double-digging, it may be better to use surface cultivation (the loosening of the upper 2 inches of the soil with a cultivating tool) for several years. In this way, the developed structure and soil organic matter are better preserved. One simple way to determine whether your soil has good structure follows. Squeeze a sample of reasonably moist soil firmly in your hand. Then open your hand. If the soil falls apart easily, it does not have good soil structure. If it holds the shape of your hand even when you press it gently with the fingers from your other hand, it does not have good soil structure. If the soil breaks apart into small clumps when you press it with your fingers, it probably has good soil structure.
When surface cultivation is used, compost made without soil will be used, because soil will not be removed from the bed during the soil preparation process. Whenever the lower soil becomes compacted, the bed may be double-dug again to encourage reestablishment of a well-aerated structure.
The soil's texture is determined by its basic ingredients: silt, clay, and sand particles. Its structure is the way its ingredients hold together. With your assistance, "threads" exuded by microbial life and "glue" exuded by plant roots help to loosen a clay soil and improve a sandy soil. The goal is to create a sumptuous "living sponge cake." Bon appétit!5
5. For more information on growing soil quality and soil structure, also see "Table 20.1— Qualitative Soil Health Indicators," in U.S. Department of Agriculture/Agriculture Research Service, Soil Quality Test Kit (Washington, DC: U.S. Department of Agriculture/Agriculture Research Service, 1999); and Fred Magdoff and Harold van Es, Building Soils for Better Crops, 2nd edition (Burlington, VT: Sustainable Agriculture Network, 2000).
Good soil preparation makes grow biointensive fertility possible—up to 4 times the productivity per unit of area!
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