By Manasa Reddigari and Bob Vila | Updated Sep 24, 2020 2:05 PM
Your lawn and garden need a variety of nutrients to grow and stay healthy. Soil is an important source of key nutrients like nitrogen (N), phosphorus (P), and potassium (K), but it doesn’t always contain them in adequate amounts. That’s why many homeowners rely on commercial fertilizers as a supplement. Fertilizers come in an extensive variety of types and nutritional profiles, each of which impacts your plants—and the environment—in a unique way. Read on to acquaint yourself with the types of fertilizers available on the market today, so you can shop your garden center for the right solution with confidence.
Fertilizer supplies plants with three primary nutrients: nitrogen, phosphorus, and potassium. This nutrient trifecta is so important to the health of plants that all fertilizers display an NPK value on their packaging. The NPK value represents the percentage by volume of nitrogen (N), phosphorus (P), and potassium (K) that a fertilizer contains. For example, a fertilizer with an NPK value of 16-16-16 contains 16 percent nitrogen, 16 percent phosphorus, and 16 percent potassium (the remainder of the fertilizer comprises filler ingredients). It also means that the fertilizer has an NPK ratio of 1:1:1; that is, it contains equal amounts of the three main nutrients. Similarly, types of fertilizer with the NPK value of 24-8-16 contain 24 percent nitrogen, 8 percent phosphorus, and 16 percent potassium—that’s an NPK ratio of 3:1:2.
Before choosing a fertilizer, determine the optimal NPK ratio for your soil by determining the existing nitrogen, phosphorus, and potassium levels using a soil nutrition testing kit (available for $8 to $25 at home centers, nurseries, and online).
With the proper NPK ratio for your soil in mind, you’ll seek out that set of numbers in one of the two main types of fertilizers on the market: organic and synthetic.
Plant, animal, or mineral remains that are packaged and sold either in their raw state or as pellets are called organic fertilizers. These environmentally-friendly fertilizers typically contain naturally occurring and therefore lower concentrations of individual nutrients than synthetic fertilizers. Home gardeners may pick them for this reason in order to help keep the fertilizer from building up in soil and either burning (i.e. killing) plants or contaminating local water sources via runoff.
Organic fertilizers—which include cottonseed meal, fish emulsion, bone meal, and blood meal—contribute beneficial microorganisms to soil that will assist in improving its structure over time, which makes it better able to hold water and nutrients. Organic fertilizers also water-insoluble, meaning they won’t dissolve with irrigation. One downside, however, is that organic fertilizer takes significantly longer to improve your plants than liquid or quick-release synthetic fertilizer does. Once spread over the soil surface, organic fertilizers must be organically decomposed by bacteria before releasing nutrients to the soil. Depending on the specific brand and mixture, most organic fertilizers supply nutrients for between three months and 10 years—so even though these fertilizers cost more than the average synthetic fertilizer (typically running anywhere from $.75 to $3 per pound), they generally require less frequent reapplication. Organic fertilizers work well for both garden or lawn applications.
Synthetic fertilizers are formulated with chemically processed compounds such as ammonium nitrate or urea. These fertilizers provide a robust source of primary nutrients but don’t contribute any microorganisms to the soil, and therefore the soil’s structure and water retention remains the same. Compared with organic fertilizers, synthetic fertilizers are more affordable (around $.50 to $2 per pound) and improve plants more quickly. The flip side to that fast action, however, is that they won’t supply nutrients to the soil for as long—only two to eight weeks, depending on the fertilizer—while organic fertilizers provide nutrients for as long as it takes the microorganisms to decompose them. While these types of fertilizers require more frequent application, over-application can lead to fertilizer burn, run-off into local water sources, and even the destruction of existing microorganisms in the soil. If you choose a synthetic option, always carefully follow manufacturer’s recommended amount and instructions.
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