Amending Garden Soil
The structure and quality of your garden soil is the foundation of your garden. It determines whether your plants will get the right amounts of what their roots need to grow: water, oxygen and nutrients. "While not all gardens have perfect soil, each one can become an ideal growing environment with the addition of amendments and by choosing the right plants," says Mike Maddox, director of the University of Wisconsin-Extension Master Gardener Program.
Soil status check If you are digging into your soil for the first time, take a good look at what your shovel turns up. Is the soil wet and sticky? Does it smear like clay on the spade? Is there sand right below the surface, with grainy soil on top? Is it so hard you can barely get the shovel in? Does it come up in rock-like chunks? If your answer is yes, read on. Garden soil should be damp and crumbly and full of earthworms—a sign there is the right amount of water, air and microorganisms in there.
Shape up with soil amendments Whether your garden soil is sandy, clay, or compacted, the best way to get it in shape is by adding organic material such as compost. This can be backyard compost you create with leaves, grass clippings, yard waste and kitchen scraps, or manure compost from the garden center. "Organic matter loosens things up, adds air space so roots can grow, and allows it to drain. It also will help hold moisture in sandy soil," Maddox says. How do you actually amend soil? Add an inch or two of compost on top, then using a shovel or heavy garden fork, turn it over up to the depth of the shovel blade. Keep turning it over and over in this manner. You can also use a rototiller to work in soil amendments, but don't overdo it, Maddox warns. "Rototilling will actually destroy your soil if you do it too much. It can pulverize it." Maddox says it is best to amend your soil in the fall. But if you didn't, wait until the soil is dried out in the spring. In addition to texture, soil also has other properties you might want to measure scientifically to see what you are working with and what your garden or lawn might need in terms of amendments and fertilizer. Things such as nutrient content, acidity and alkalinity can be measured by a soil test. What's your NPK? According to the University of Wisconsin-Extension, a soil test will tell you what nutrients your plants or lawn need and will recommend the amount of fertilizer (N-P-K) to add to your soil. The N stands for nitrogen. Nitrogen encourages fast, green growth. The P stands for phosphorus. Phosphorus stimulates root development, rapid growth, and quality flowers. The K stands for potassium and promotes disease resistance, strong stems and winter hardiness. Test the pH A soil test will also tell the current pH of your soil. Soil pH is a measure of soil acidity. Acidic soils have a pH lower than 7.0. Neutral soils have a pH of 7.0. And soils with a pH about 7.0 are called alkaline. Most plants will grow adequately up to a soil pH of 7.5. Some plants, such as blueberries and azaleas, love acidic soil (low pH) while other plants, such as tomatoes and carrots, prefer alkaline soils (high pH). In reality, most garden plants and flowers tolerate a range of pH, Maddox says. You can change the pH level in your soil by adding soil amendments. For example, adding sphagnum peat makes soil more acidic. Adding pulverized limestone, or lime, makes soil more alkaline. "If you are going to attempt to change the pH level of your soil, do it a year in advance and retest it," Maddox suggests. You can buy a soil test kit in garden centers, or contact your local university extension office. They usually offer soil testing to homeowners for a small fee. Match your plants to your soil type Ultimately, it might be best to simply work with what you have, and match your plants to your soil, Maddox says. Search online for plants that grow in your type of soil, use university extensions from your region as a resource, or call your local botanic garden or arboretum, he suggests.