Preparing Your Garden's Soil
March is the month that gardeners become eager to start planting. You can dig up and work your soil as soon as it is dry enough. With sandy soils you can start whenever you like, but test clay or silty soil to see if it is dry enough.
Squeeze a handful of soil into a ball in your palm. If the lump falls apart easily when you tap it, it's ready. If it dents but holds together when you tap it, let it dry out some more. Working wet soil will hurt its structure and make clods that will dry like bricks.
Good soil is 50 percent solids and 50 percent porous space, which provides room for water, air, and plant roots. The solids are inorganic matter (fine rock particles) and organic matter (decaying plant matter). The inorganic portion of the soil can be divided into three categories based on the size of the particles it contains. Clay has the smallest soil particles; silt has medium-size particles; and sand has the coarsest particles. The amount of clay, silt, and sand in a soil determine its texture. Loam, the ideal garden soil, is a mixture of 20 percent clay, 40 percent silt, and 40 percent sand.
To test the sand, silt, and clay content of your soil try this simple test. First collect a sample of dirt from your garden. Add about 1 cup of dirt to a 1 quart Mason jar, fill the jar 3/4 full of water, and add a drop of dish soap to help break up the particles. Then shake the jar to mix up and break apart the soil. Finally, let the jar set for a few hours so the particles can settle to the bottom. The heaviest sand will be on the bottom, silt will form the next layer, and clay will be on top. This should help you judge the contents of the soil.
When you work your soil, add organic matter and fertilizer, as well as lime, if needed. Compost, manure, peat moss, grass clippings and aged sawdust are the kinds of organic matter that will help build your soil. Add as much as you can now and keep digging it in through the season. If you have a very sandy, or a heavy clay soil, organic matter is your best friend. It will improve the worst soil and make an average soil a joy to work.
For the fertilizer, use whatever you have or can buy inexpensively. The three numbers (15-10-10 or 6-10-7) on any fertilizer package give the percentages of nitrogen, phosphate and potash. Make sure your fertilizer has some of all of these elements. You could start with about three pounds (pints) of 5-10-10 per 100 square feet. If your fertilizer is stronger (10-20-20), use less.
Don't forget to add lime. It's best to apply lime when the soil is as dry as possible, allowing it to be mixed in well. Ideally, lime the soil in the fall. It will have adjusted the pH by spring planting time. Most veggies (potatoes are the exception) would prefer a pH between 6.5 and 7.0. A soil test will give you specific recommendations. General guidelines are: for every 100 square feet of sandy soil--4 pounds, loam--6 pounds, clay-like soil--8 pounds. Reapply lime every 2 years (3 years for clay soil).
After fertilizers and soil amendments, like compost, have been added it is time to till up the soil. For large gardens I recommend using a gas powered rotary tiller, but for small gardens and flower beds, double-digging works best. This method of creating planting beds is similar to raised beds in some ways. In this approach, the soil is deeply worked not with a plow, rotary tiller, or harrows, but with shovel and/or pitchfork. The approach works best when combined with planting beds as opposed to single-row or wide block plantings.
The double-dig method is aptly named because the simplest technique is to dig down two spade or shovel blade depths (see diagram below). The first spade depth is actually lifted and removed from that section of the planting bed (and returned later either into the previous section, or at the end of the bed). Then once that first spade depth worth of soil has been lifted, a second spade depth (or pitchfork depth) is worked loose to allow extremely deep root penetrations.
Maintaining healthy soil requires work, but it is worth it when you bite in the first tomato or see a perfect bloom emerge. As many gardeners know, the hard work put into creating your garden only makes the reward more worthwhile. Using these simple methods you should be able to produce a soil that is healthy and will only grow more fertile as the years pass.