4 Earthworms and soil bacteria continuously break down organic material to enrich the soil and help provide both good structure and texture. Earthworm tunneling creates pores for water and air to circulate, which in turn provides a healthy environment for soil microbes. Rich Soil or Poor Soil Rich soil is high in nutrients and contains a lot of humus; it’s typically dark and moist. The best way to maintain rich soil is to continuously add organic material, like compost, throughout the growing season. Most garden plants grow better in rich soil. Poor soil is also known as mineral soil, because it contains a low amount of organic material. Some desert and seashore plants actually thrive in poor, mineral soil; their roots would rot in the moist rich soil that most garden plants prefer. Soil Nutrients The three major soil nutrients are: Nitrogen (N), Phosphorous (P), and Potassium (K). Indeed, most commercial fertilizers are labeled according to their N-P- K concentration. A fertilizer that is labeled 10-10-10 contains 10% Nitrogen by weight, 10% Phosphorous, and 10% Potassium. (The rest of the weight is filler or carrier that facilitates spreading the fertilizer.) Nitrogen affects good leaf and stem growth; it also causes the quick greening of newly fertilized lawns. Too much Nitrogen, however, can “burn” plants and actually kill them. Phosphorous is important to root development and plays a key role in fruit ripening. Potassium’s key role is that it enhances resistance to disease. All other soil nutrients are called “minor elements” even though some are either very important or somewhat toxic to various plants. Copper (Cu), sulfur (S), and boron (B), for example, are very helpful for fruit trees; but, even small amounts of boron can be harmful to vegetable garden plants. Other micronutrients, sometimes called “trace elements,” include: Magnesium (Mg), Iron (Fe), Manganese (Mn), Zinc (Zn), and Calcium (Ca). Soil Chemistry – pH The standard measure of soil acidity is pH. The pH scale ranges from 1 to 14, with 1 representing the most acid, 14 being the most alkaline (or basic), and 7
5 being neutral. Very rarely will soil have a pH outside of the range of 4-to-8. The soil’s pH is very important, as it affects how well the soil microbes perform as well as how well the plants roots absorb nutrients. Areas with abundant rainfall typically have more acidic soils; and, all garden soils tend to become more acidic over time, as acids are created when organic matter decays. Thankfully, most garden plants tend to perform very well in slightly acidic soils … at about 6.5 on the pH scale, the point at which minerals are most soluble and therefore readily available to the plants as nutrients. Rhododendrons, azaleas, and blueberries actually prefer acidic soil in the 4.5 to 5.0 range, and most serious azalea and blueberry gardeners use special fertilizer for “acid-loving plants.” In more alkaline, or basic, soils, their leaves turn yellow because iron intake is impeded. Checking Your Soil’s pH If your lawn or garden is performing poorly, you may want to check the soil’s pH. While there are a lot of home test kits on the market, most of the soil experts recommend a professional test. The home test kits may not be very accurate, and obtaining a professional test is relatively easy and inexpensive. This is one instance where bad information may be worse than no information. If you’re going to amend your soil with anything other than good compost, make sure that you know what you have, and what you need! There are three main sources for soil tests: • Co-op or County extension services • University and Private soil labs • Most lawn care companies You simply need to order a kit (consisting of a container, instructions, and a return shipping box/envelope), and send a sample of your soil to the lab. Most simple soil tests cost about $10 to $15. You can find a lab or lawn care service in the yellow pages on the Internet. At Scottssoiltest.com, for example, you can purchase a kit for $15. Most tests will include both a pH reading and a nutrition analysis. If a soil test or your plants’ performance indicates that your soil is too acidic, the best remedy is to apply pelletized lime to move the pH upward. Of course, the amount of lime will depend on both how acidic your soil is and your soil’s structure. When making adjustments to soil pH, it is better to do so gradually; it’s better to make adjustments over two or more years.