Building and maintaining soil fertility is the best thing you can do for healthy plants. With the proper soil, your vegetables will thrive and be able to fend off diseases and pests without much help. Fortunately there are many ways to prepare garden soil and the materials needed are common to each. Some however require expensive tools and others do not. We'll start with some common materials and then do a run-down of the methods for getting your garden started off right, from the ground up.
Soil Amendment Basics
Most important is to know what it is you want to grow and have some familiarity with your soil profile and depth. Testing the soil is free through Agricultural Extension offices found all over the country, so look up yours for specific directions.(1) Many residential areas, especially in the south, were stripped of topsoil by developers, and several of the methods will help with this.
No matter what kind of soil you have, you'll want to add organic matter in the form of compost. This can be bought or made. Many people make compost without thinking about the microbial needs, and it tends to be only half-finished.(2) The best mixture is 20:1 Carbon to Nitrogen. Dead and dried plant materials have more carbon than nitrogen. Newspaper for instance has an 800:1 ratio. Dry leaves are 50:1, and fresh leaves are 30:1. Vegetable waste, like scraps from the kitchen, are around 12:1. Toby Hemenway in Gaia's Garden (highly recommended) offers excellent tables of different compostable materials and suggestions on finishing compost.(3)
Organic fertilizers are useful and a soil report from your County Extension office an help you determine what the soil is lacking. The major nutrients are Nitrogen, Phosphorous, and Potassium. A mixture of bat guano, rock phosphate, and either greensand or wood ash will generally provide everything your soil needs by way of nutrients. Certain plants will send roots down to rock in the soil and bring up nutrients. Clovers, alfalfa, and comfrey are excellent plants for green manure, helping to build and sustain fertility over time. Green manures are cover crops that can be harvested for the compost pile or, in the case of clovers, left in the garden as cover crops and planted around.(4)
Finally, you'll want some balance in your soil profile. If it's too heavy with clay, organic matter will certainly help, but you may add some sand as well. If it's too sandy, organic matter is going to help a lot. Just take a look at what these permaculturists did in the desert of Lebanon for inspiration.(5)
Soil Preparation: Tilling
Traditional tilling certainly is not the most labor intensive of tasks, but look closer. It takes money to buy or rent that tiller and feed it with gas, money you had to work for. The soil also has to work harder, because tilling does a lot of damage to the lifeforms (microbes and fungi) that make for the best soil. Of course, tillers do mix soil amendments in well, and they do make quick work of aerating the soil, both bonuses. Many people can't imagine having to prepare soil with a shovel after using a tiller. I'm here to tell you, you can get away without using a shovel or tiller, and you'll have healthier soil. First though, let's see what the shovel can do.
The French method of double digging offers a way to increase your harvests off a small space. By providing the plants two feet of loose, aerated soil, their roots will go down instead of spreading out along the surface. This has the added benefit of protecting them from drought conditions.(6)
However, this method requires a LOT of work the first time you do it. Digging down two feet is hard enough, but a major goal is to also maintain soil structure. Certain microbes only live in the top inch of soil, others always live a foot down. If you change their places, then they will die and cost you soil fertility. This method requires a lot of attention to where each shovelful of dirt goes. You take it off the bottom, it has to go back on the bottom. Fortunately, most of the work is up-front. If you don't compact the soil with footprints, it will maintain the new structure and be much easier to dig next season. Double digging really works well for increasing production in small space and keeping plants healthy.(7)
Building the Soil Up: Sheet Mulching and Lasagna Gardening
Sheet mulching is not as tough on the back, since it's a no-till no-dig system, but it can take a little time. A very similar method is lasagna gardening, and your choice will depend on what materials, and how much time, you have available. The idea is to compost in the garden, and let the vegetables be part of the composting process, just like what happens in nature. Take a look at a forest floor, and see how the materials are layered on one another.
There are several recipes, but this is the easiest:
1. Put down six inches of food scraps, grass clippings, and/or manure (worm castings are very good, horse manure will warm your soil more quickly in the early spring);
2. Cover this with several layers of newspaper or a layer of cardboard, and make sure to get it all wet;
3. Finish with a six inch layer of mulch, make it high nitrogen material like straw, wood chips, and/or dry leaves;
4. You can plant immediately, or let it sit for a few weeks.(8)
Patricia Lanza, of lasagna gardening fame, suggests that any organic materials (excepting fat, meat, and bone) will work. On top of your wet bottom layer, add a layer of peat moss, then a layer of organic material (like compost, leaves, or manure) then another inch or two of peat moss.The more diverse materials used, the better. Between layers is a great place to throw kitchen scraps and fertilizers, and you can later peel layers back and add more. Keep doing this until you have a height of 18 inches or more. Mulch the top and sides to prevent erosion. Over time, your mound will shrink somewhat, and the many earthworms to come will loosen the soil beneath your mound, giving your plants even more room to root.(9)
Hugelkultur and the Dead Wood Swale
Hugelkultur (Hoo-gail-kool-ture or hoogle culture) and dead wood swales are the final and, to me, the most interesting techniques for preparing garden soil. They both make use of something we often have in abundance, particularly after storms, tree branches. Woody waste does not do well in the compost, so why not use it in the garden? Have you ever noticed how well rotting wood holds water? These methods use that to the gardener's advantage.
Hugelkultur is a pile of branches and twigs 1-2 feet deep, stomped down for compaction. Fill in space between the wood with material like grass clippings or straw. Add a thin layer of compost, an inch of topsoil, and plant your seeds immediately. You may want to correct the underlying soil pH balance beforehand, but it's unnecessary. These beds will slowly be fertilized by the rotting wood, and your plants will be happy without much else. Potatoes and vining plants have been noted to prefer and thrive with hugelkultur.(10)
The dead wood swale is quite similar, but it involved burying a log underneath the area you want to plant. This is best done for perennials that are not drought-tolerant, like berry bushes. The same rules apply, except more attention should be paid to soil pH, as much because berries like a more acidic soil than anything else.(11)
Once you've put in the more or less hard work of building a garden bed, don't let it go to waste. Any farmer worth her salt knows that the hard work is up front, and the little organisms living in the soil will do the rest. To help them out, always keep the ground covered with something. When tomato season is wrapping up, go ahead and plant hairy vetch between the tomato plants.(12) Vetch has been shown to increase tomato production when grown first, so you'll have a head-start on next year.
Finally, if you're soil has been abused like most residential area soils have, then you should look into a multi-fungal and microbial additive to jump start healthy soil processes.(13) One root zone addition is available from Bountiful Gardens and another from Fungi Perfecti. Whatever the source, these differing strains of fungus and bacteria have been shown to help plant roots absorb nutrients and find water. Healthy soil requires that the nutrients not only be available but also accessible. Happy Gardening!