Practice No. 6. Minimize Subsequent Soil Disturbance
Soil disturbances can be caused by overworking the soil and by compaction. The downside is disruption in healthy soil structure and of the soil food web. Our model is nature itself. Look to the meadow, the prairie, the forest, alpine tundra or any natural ecosystem for keys we can follow.
Avoid Overworking Soils
Although garden and vegetable beds can be created by direct planting in the soil, initial amending of beds with correct amounts of organic matter and inorganic amendments for heavy clay and caliche soil yields far better and more reliable results. Our clay and caliche soils benefit from the aeration caused by working in amendments along with the inclusion of organics/inorganic amendments and leading to increased beneficial soil life. After establishing beds with adequate organic and/or inorganic matter, apply 2-4 inches of organic mulch depending on the type of plants used, usually for medium and high water-use and high feeding plants (low water-use plants prefer inorganic mulches). The mulch breaks down, adding organic matter to the soil. A mulch that breaks down more quickly than wood chips may be desirable for a number of years in newly worked soil. Compost added to the top of established beds before covering with wood chips is ideal.
Minimize subsequent soil disturbance by minimizing rotor tilling; no-till gardening is recommended. Yearly and especially excessive rotor tilling and digging, even annual tilling deeper than a few inches, upsets and kills earthworms and micro organisms alike, putting your soil in a constant recovery mode.
Mycorrhizal and other fungi produce fungal hyphae that can grow in length as long as feet or yards, bridging gaps to locate and transport nutrients and water to plants (http://soils.usda.gov/sqi/concepts/soil_biology/fungi.html). It takes time to develop a network in aiding trees and other perennials. Likewise, disturbance by using fungicides kill beneficial fungi as well.
The addition of oxygen and subsequent nutrient release caused by over tilling and repeated tilling is more than can be used by plants, resulting in the unused nutrients leaching out of the root zone, a wasteful process. This in turn causes excessive amending in the following years.
Like all good rules, there are exceptions. Fall cultivation is recommended as an organic remedy to break the recurrence of pests that overwinter in the soil, such as cabbage loopers, carrot weevils, certain species of fruit flies, beetles, earworms, borers, grasshoppers, harlequin bugs, leaf hoppers and others. Turning over the soil in the fall, particularly after a few frosts, exposes the larvae to frost and freezing temperatures. If faced with some of these problems and if planting a fall and winter vegetable garden, rotate your crops and/or periodically leave areas fallow for fall cultivation in lieu of fall planting.
Making Raised Beds
When faced with poor compacted soil, creating a raised bed may be the best solution. Raised beds can be planted more intensely than regular beds. Amend with composted and other organics by topdressing or lightly scratching the soil surface. Raised beds offer all the advantages that soil with great drainage offer:
- Adequate oxygen available for the root growth
- More water available for the roots
- Better root development
- Easier to plant, weed, and maintain
- Longer planting seasons due to earlier warming; heat is held in the soil longer in the fall
- Handicapped accessible beds allows horticultural therapy and enjoyment that is otherwise not feasible
- Raised beds allows the gardener a place to sit while gardening (this becomes more important the longer one gardens).
Raised beds should be at least 12-16 inches tall or taller. The width of raised beds should not be wider than twice your comfortable reach when you have access on all sides. Length is a matter of space, need and your energy to build it. Do not use treated wood in the construction of the bed, wood or products that contain chemicals than will leach into the soil. For growing any food, never use wood treated with arsenic (chromated copper arsenic or CCA), creosote or pentachlorophenol. If you currently have these materials, line the bed with a heavy enough plastic or non-permeable barrier between the material and the soil.
Lasagna Gardening Another method of starting a bed is to layer organic and inorganic material on top of the soil, called lasagna gardening or sheet composting. Fall is the best time of year to start allowing for the decomposition of materials and growth of soil life when planning for spring planting. Lasagna gardening will work any time of the year.
If you are planting over fescue or bluegrass turf, cut the grass (with a mulching mower, preferably). It's helpful to poke holes with a garden fork or loosen with a spade, (don't turn the sod) throughout the area, adding a thin layer of wormcastings, rabbit or chicken manure; watering it in good. The next day, place overlapping layers of regular newspapers, about 2-4 sheets thick, (not glossy magazines) or a sheet of corrugated cardboard over the turf with an inorganic amendment to hold the newspaper in place. Water this in. Add layers of composted manure, leaf mold and grass clippings 2 to 4 inches thick, watering these as well several times, to the consistency of a wrung out sponge. In other words, not flooded but moist all the way through. Add a 3-8 inch layer of straw. Water in. Top with an inch or two of composted plant or animal matter, topping with an inch or two of weed free straw, fine shredded bark or wood shavings, moistening each layer.
Allow six months before planting for best results. If you need to plant quickly, make little pockets about 3 inches deep filled with soil or compost. The bigger the plant, the larger your pocket. Gaia's Garden, A Guide to Home Scale Permaculture, by Toby Hemenway, (Chelsea Green Publishing Company, 2009), a reference used for this section, would be an excellent addition to any gardener's library. Filled with sustainable techniques that can be applied to our climate, Toby gardens in Oregon.
Hugelkultur On a lot with trees and shrubs, there are always twigs, branches, stems, even logs to dispose. In alternative to hauling them off to the chipper is to use these woody materials on site. Raised garden beds made with brush, hugelkultur, can be made by burying them in a few inches of soil, stacking up to a foot or two deep, stomping them down to compact the pile. Water this in before adding a layer of other compostable materials, moistening again. Add a thin layer of compost, then an inch or two of soil, moistening again.
I've not tried this method used in Eastern Europe and other forested regions where they claim only minimal, or no, subsequent watering. In our hot, dry and cloudless climate, I doubt this would be possible. We even have to water our compost piles! No fertilization is needed as the brush slowly decays, releasing nutrients. Hugelkultur beds are used initially for planting potatoes, squash and melons, then other crops over the years.
Avoid Soil Compaction
Avoid compacting the soil in beds and borders by walking directly on the soil. Especially do not walk in the beds after watering or rainfall when the soil is wet. Lay planks across the beds or heavily mulch soil with straw, even over six inches thick. Walking on wet soil destroys the soil structure you've worked so hard to build. If the beds are large, create permanent pathways with mulch or stepping stones.
Lawns are meant to be walked on, and can become compacted as well. Large heavy tractor and riding mowers that follow repeated mowing patterns create compaction. Aerate at least yearly, in the spring and again in the fall if necessary. Apply fine grade compost or other amendments immediately after aeration.
Doubtless, gardeners have applied variations to the soil building techniques and practices given, but the principles remain the same: creating healthy soil in some fashion to stimulate the growth of beneficial soil life and provide long-term nutrient release with minimal subsequent soil disturbance.