Fertilizing gardens and landscape plantings is not a one-size-fits-all proposition when it comes to selecting the right combination for your yard.

Choosing a fertilizer based on price or the size of the bag is a recipe for disaster. A fertilizer’s value depends on the total amount of nutrients or plant food within the fertilizer.

Before buying any fertilizer, a soil test in the garden or landscape area is recommended. Soil-test mailing envelopes are available at County Extension Offices for $9.

The soil test can detect whether fertilization and lime application is even necessary. Too much fertilizer or lime can interfere with plant growth.

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

The percentage of nutrients is 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 of fertilizer, 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. 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. Leafy crops like lettuce, spinach, cabbage and even turfgrass benefit from higher applications of nitrogen, which means you should look for a product with a 2:1:1 ratio or higher.

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.

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. 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.

“Growing Green” is contributed by Lehigh County Extension Office Staff and Master Gardeners. Information: Lehigh County Extension Office, 610-391-9840; Northampton County Extension Office, 610-746-1970.