Gardeners should test soil before they plant

Preparing the soil is the most important step in flower or vegetable gardening, according to an extension expert in Penn State's College of Agricultural Sciences, who advises gardeners to have their soil tested this spring and to use the test results and recommendations as a guide.

"The soil in gardens changes, although it may look the same year after year," said Robert Berghage, associate professor of horticulture. "Growing and harvesting crops, leaching and erosion affect the availability of soil nutrients. A soil test is a valuable tool that guides gardeners."

A soil test measures nutrient amounts and pH, or level of acidity. Soil pH is measured on a scale of 0 to 14, with 0 being the most acid, 14 the most alkaline and 7 neutral. Most soils naturally have pH levels ranging between 5 and 8. "Many flowers do well in a range between 6 and 7, so chances are you won't need to change your soil's pH much," Berghage said. Don't guess when it comes to fertilizing and changing pH, Berghage cautioned. Overapplying chemicals can harm soil and plants, as well as pollute groundwater and streams.

"Excess lime raises the soil's pH above what plants can tolerate, makes it more difficult for them to draw nutrients from the soil and slows growth of beneficial soil microorganisms," Berghage said. "Some flowers prefer a more acid soil and can suffer from iron deficiency if you apply too much lime."

Soil test kits are available at Penn State Cooperative Extension county offices and larger garden centers for a nominal fee. County extension kits include instructions for collecting soil samples, and sending them to Penn State's soil-testing laboratory. Samples can be mailed or delivered to the laboratory.

Participants will receive test results in about two weeks. Results include levels of potassium, calcium, phosphorus and magnesium, along with the soil's pH. Also included are recommendations for the kinds and amounts of fertilizer to apply and how much lime -- if any -- to add to the soil.

"If you're planning to grow rhododendrons, azaleas, laurels or other flowers that prefer acid soil, you may need to apply a chemical such as sulfur, which lowers pH," Berghage said. "Apply no more than the recommended amount."

Till the recommended materials about 5 inches into the soil. While working the soil, remove stones, sod clumps, weeds and debris. "Incorporate several inches of organic matter," Berghage said. "There's little danger of adding too much. Composted kitchen scraps, well-rotted manures, lawn clippings and decayed plant material all are good forms of organic matter. They help retain water and supply some nutrients for all plants set into the soil."

Add 2 to 3 inches of organic mulch on top of the soil around your plants. Mulch helps keep soil moist, prevents erosion, discourages weeds and builds up the soil's organic matter. "Mulch also tends to be more attractive than bare soil in an ornamental garden," Berghage said. "It keeps mud from splashing on your flowers and gives the ground's surface uniform color and texture."

Several kinds of mulch are available at garden centers, including wood bark chips, shredded bark and peat. People who use grass clippings, leaves or well-decayed compost, should periodically loosen them with a hand cultivator or hoe to prevent surface crusting.

When plants begin to flower, use a high-nitrogen fertilizer on the soil about 6 inches away from the base of each plant. Follow product application rates. This will enhance flowering and give plants a boost for the rest of the summer. "If you fertilize too soon, however, you will delay the plants' maturity and decrease the number of flowers," Berghage said. "Wait until the first flowers open."

Finally, retest the flower garden's fertility and pH levels each year for several seasons. If reports remain similar, gardeners can reduce sampling to every three to four years. "Nutrient levels and pH gradually change over time," Berghage said. "It's important to keep monitoring the soil to keep levels optimum."

Soil test kits may be purchased for $9 from 8 a.m. to 4:30 p.m. Monday through Friday at Penn State Cooperative Extension offices or in 111 Agricultural Analysis Services Laboratory, Tower Road, University Park, PA 16802. For more information, go to the Web at http://www.aasl.psu.edu/SSFT.HTM