The importance of soil fertility Key to having healthy landscape plants

The importance of soil fertility

Key to having healthy landscape plants

by Timothy Daly, UGA Extension Gwinnett

Large sums of money are spent installing new landscapes, and sometimes the plants perish. Many problems can be the source of the difficulty, but one sticks out in particular: the condition of the soil, which is the most critical component of a plant's environment.

From soil, the plant obtains water, nutrients, and even air. The ideal type of soil for a plant is fertile, deep, well-drained, and has high organic matter. Many essential nutrients are necessary for optimal plant growth. The major nutrients, which the plants require most, are nitrogen, phosphorus, and potassium. The secondary major nutrients are sulfur, calcium, and magnesium. Then plants require micronutrients, which are only needed in small quantities. Zinc, iron, manganese, molybdenum, boron, and copper are some of the micronutrients. Regardless of the type of nutrient, if any are deficient, the entire plant will suffer. Different plants have differing fertility requirements.

The importance of pH

Of the many factors that affect nutrient availability, the most important is the soil pH, which measures the soil's acidity. The pH scale ranges from one to fourteen. Seven is considered neutral, and below it, the soil is acidic, and above it is alkaline or basic. The scale is logarithmic, meaning that a pH of six is ten times more acidic than seven, a pH of five is 100 times more acidic, and so forth.

Most plants require a pH of 6.0 to 6.5, which is the level at which most essential elements a plant needs are available and can be absorbed. Outside that range, their levels are too low for the plant to take up. However, several exceptions exist. Iron, zinc, and manganese are in higher quantities at a pH below six. Some plants

require higher amounts of iron thus grow better at a lower pH. Azaleas, rhododendrons, mountain laurels, blueberries, and camellias need more iron to grow properly. If the pH is too high, an iron deficiency develops, and the plants develop chlorosis, which causes the leaves to turn light green, yellow or white between the veins. If the pH is too low, the addition of lime will increase it. If it is too high, applying sulfur or a compound with sulfates such as ammonium sulfate or iron sulfate will reduce the pH.

Don't guess, test

Consider having the soil tested for a minimal fee through the University of Georgia Extension. Go to ugaextension.org or call 1-800-ASK-UGA1 to find the

Extension office that is most convenient to you.

The most critical step in soil testing is collecting the samples. Here is how to take a soil sample: 4 Using a small shovel, dig out a one-inch-wide soil core four inches long for turfgrass and six inches for other plant material. 4 Take at least ten to twelve random samples from the area and thoroughly mix them in a container. 4 Place two cups of the mixed soil into a plastic bag and make sure it is dry. 4 The samples should not include plant roots or other accumulated organic matter and need to be dry—separate samples for each type taken. 4 For example, if you have a property with fescue in one area and ornamental trees and shrubs in another area, take two separate soil tests: one for the fescue and the other for the ornamental trees and shrubs.

You will receive the results within 7 to 14 days by mail or e-mail. The soil tests results include pH, phosphorus, potassium, calcium, magnesium, zinc, and lime levels. It does not test for nitrogen since this element changes forms in the soil and can fluctuate widely throughout the season. The test gives recommendations for nitrogen based on what research has shown the type of plant material requires. It will indicate what types of fertilizers are needed. The lime and nutrient recommendations are given in pounds per 1,000 square feet or per acre. Test results will tell you what types of fertilizer should be applied, how much you need, and when to use it. These recommendations are specific to whatever kind of plant material you want to grow (as written on the soil test record sheet). If you have questions, contact your Extension Agent.

Go organic

Another essential component of healthy soil is organic matter, improving its fertility, moisture retention, aeration, and drainage. Several types of organic matter can be used, including peat moss, topsoil, animal manure, and compost. The organic material helps break up the heavy clay to allow improved air and water movement. It also helps improve drainage while retaining enough water for the plants to absorb. Organic matter encourages beneficial soil organisms, such as microbes, insects, and earthworms that decay organisms and release nutrients into the soil. It also reduces erosion and storm-water runoff while decreasing soil crusting and compaction.

Use care when incorporating organic matter into the soil to ensure the material is completely decomposed. Fresh wood chips, such as those produced by tree care companies, need to undergo decomposition by micro-organisms to make usable material. In the process, they will take nitrogen and other minerals required for plant growth out of the soil, thus potentially causing a deficiency.

However, the material can be used as mulch and placed on top of the soil. On completion of the process, which can take several months to a year or more (depending on the type of wood and environmental conditions), the wood chips can then be incorporated into the soil.

Do not incorporate any organic material into the planting holes of trees and shrubs. Just fill in with the existing soil that has been removed. The organic matter can inhibit water drainage and reduce the roots' ability to spread into the existing soil since the growing conditions are more favorable in the surrounding organic material.

The soil is one of the most critical components of growing healthy plants. It provides anchorage, nutrients, water, and other essential materials. By improving the soil quality, you will improve the quality and beauty of the landscapes you are installing and maintaining.

About the author Timothy Daly is an Agricultural and Natural Resource Extension Agent with UGA Extension Gwinnett. He can be contacted at 678-377-4011or tdaly@uga.edu.