Choosing A Fertilizer
"Choosing a fertilizer based on price or the size of the bag is a recipefor disaster," says J. Robert Nuss, professor of ornamental horticulture inPenn State's College of Agricultural Sciences. "A fertilizer's valuedepends on the total amount of nutrients or plant food within thefertilizer."
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Before buying any fertilizer, Nuss recommends testing the soil in the gardenor landscape area. Soil test kits are available at most cooperative extensioncounty offices and at many larger home centers, garden centers and hardwarestores.
The soil test can detect whether fertilization and lime application is evennecessary, Nuss explains. Too much fertilizer or lime actually can interferewith plant growth.
A complete fertilizer that contains nitrogen, phosphate, and potash generallyis best for most garden or landscape plants. Although fertilizer formulas are abit daunting to the uninitiated, Nuss has several suggestions on fertilizing:
- 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. For example, 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 turf grass will 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.
