UNIVERSITY PARK, Pa. -- Fertilizing gardens and landscape plantings is not a one-size-fits-all proposition when it comes to selecting the right combination for your yard, says an expert in Penn State's College of Agricultural Sciences.

"Choosing a fertilizer based on price or the size of the bag is a recipe for disaster," says J. Robert Nuss, professor emeritus of ornamental horticulture. "A fertilizer's value depends on the total amount of nutrients or plant food within the fertilizer."

Before buying any fertilizer, Nuss recommends testing the soil in the garden or landscape area. 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 can detect whether fertilization and lime application is even necessary," Nuss explains. "Too much fertilizer or lime actually can interfere with plant growth. With repeated annual applications of phosphate fertilizers, eventually the soil can accumulate high levels since phosphate is held in the soil unlike nitrogen and potash, which are either used up or leach out before the next growing season. This is one of the reasons it is important to get the soil tested regularly to determine what fertilizers are actually needed."

Nuss says that a complete fertilizer generally is best for most garden or landscape crops. A complete fertilizer contains nitrogen, phosphate and potash. Although fertilizer formulas are a bit daunting to the uninitiated, Nuss relies on several easy tips to help first-timers learn how to fertilize:

The percentage of nutrients is always listed on the bag in this order: nitrogen, phosphate and potash. For example, a 10-5-5 fertilizer would contain 10 percent nitrogen, 5 percent phosphate and 5 percent potash.

To see what kind of value there is in a package, determine how many pounds of nutrients there are relative to the rest of the package. "An 80-pound bag of 10-5-5 fertilizer would contain 8 pounds of nitrogen, 4 pounds of phosphate and 4 pounds of potash," Nuss points out. "The remainder of the package is filler and carriers for the nutrients."

How plants respond to fertilizer is determined by the ratio between the three nutrients. Fertilizer ratio is determined by dividing the lowest number in the grade into each of the numbers in the grade. By dividing 5, the lowest number in the fertilizer grade, into the 10-5-5 grade, the resulting ratio is 2:1:1.

"Fertilizer ratios are very important when selecting a fertilizer mix," Nuss says. "Leafy crops like lettuce, spinach, cabbage or even turfgrass will benefit from higher applications of nitrogen, which means you should look for a product with a 2:1:1 ratio or higher."

Nuss says landscape plants and fruit-producing crops do not need higher nitrogen levels and would benefit from fertilizers with a lower nitrogen level, such as the ratio 1:2:1. He warns that buying the biggest bag, even if it has the correct fertilizer ratio, isn't necessarily the best bargain.

"Calculate how many pounds of actual nutrients you are getting for the price," Nuss advises. "A large bag of fertilizer with fewer nutrients may be more expensive in the long run. Buying products based on quality rather than quantity can help your budget and make your plants happier."

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Contact: Jeff Mulhollem jjm29@psu.edu 814-863-2719 814-865-1068 fax #167