UNIVERSITY PARK, Pa. -- As chillier temperatures usher in an end to your vegetable garden, warm up to the idea of testing your garden soil to ensure that the soil pH is up to snuff, says a gardening expert in Penn State's College of Agricultural Sciences.

"If you're starting a new garden or have just moved to a new home and want to start a garden, you have to take a soil test to get an idea of how the site was used," says Pete Ferretti, professor of vegetable crops. "Some experts can tell if soil is acidic or alkaline by looking at the weeds growing, but that kind of expertise is beyond most of us."

Ferretti recommends testing the soil in late summer or early fall to allow enough time to apply soil additives if needed. Soil test kits are available at all Penn State Cooperative Extension county offices and at many larger home centers, garden centers and hardware stores.

"The soil test will come back with a written recommendation," Ferretti says. "It will give the consumer a rate of application and list any additional soil amendments."

Ferretti says all test results will give application rates in pounds-per-100 square feet. In most cases, soil tests will recommend applications of lime to raise the pH of garden soil. Other soil amendments include calcium and magnesium.

"Most of the soils in the state are naturally acidic because Pennsylvania gets a lot of rainfall, which percolates into the soil raising the acidity level over time," Ferretti says. "That's why gardeners should test soil the first two years of the garden's existence and every third year after that."

Ferretti says bags of lime are widely available at any garden center, hardware store or home store. He warns gardeners not to blindly choose the first bag of lime they see, however. He recommends finely ground limestone, which has the consistency of talcum powder.

"Finely ground lime is of the right consistency to work into the soil over the winter," Ferretti explains. "Coarse limestone -- which has the feel of play sand -- will eventually work into the soil, but it will take a few years."

Ferretti warns consumers never to buy limestone-based products called "quicklime," "burnt lime" or "slaked lime," all of which are so finely ground that they feel like powdered sugar. "These products are used in the construction industry, primarily by masons," he says. "An application of these products will raise the pH of the soil, but it is so caustic that it burns roots, and the increased pH level will not last more than a few weeks."

Ground limestone products also are available with added magnesium or calcium. The percentage usually is listed right on the bag, Ferretti says. "If you use lime with the correct amount of magnesium or calcium, it saves you a much more expensive individual application of Epsom salts, which contain magnesium, or gypsum, which contains calcium."

If soil test results deliver a recommendation of more than 6 pounds per 100 square feet, Ferretti suggests applying half in the fall and half in the spring to prevent overapplying lime. "The best time to apply is from September to early December," he says. "Any time is fine, but make sure the ground is not frozen, or the application will be washed away."

Ferretti says there are a few crops that require acidic soil to thrive, including blueberries, bramble fruits such as blackberries and raspberries, mountain laurel and rhododendron. "Strawberries grow best in slightly acidic soil," Ferretti adds.

Once the garden soil has reached the desired level, Ferretti recommends applying between 5 and 6 pounds per 100 square feet every three years to maintain proper pH. "Make sure you weigh it accurately," Ferretti says. "If you don't have a small scale, use your bathroom scale. You can measure into a 3-pound coffee can or similar clean container and mark the 2.5- or 3-pound level on whatever container you use to apply the compound. That way, you can use that container year after year without measuring each time."

Ferretti says gardeners should not expect an application of lime to completely cover the garden. "The garden should look like a dusting of powdered sugar on a cookie or cake," he says. "If it looks like a field of snow, you probably over-applied."

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EDITORS: For more information, contact Pete Ferretti at 814-863-2313.

Contacts: John Wall jtw3@psu.edu 814-863-2719 814-865-1068 fax