Many gardeners and homeowners harbor the misconception that more is better where fertilizers are concerned, believing that if a small amount causes greening or plant growth, then a larger amount will produce an even greater positive effect. In fact, the opposite is true, and in addition to the potential for harm to the local environment, fertilizer overuse can potentially damage your plants as well.
Fertilizers generally provide at least three major nutrients to plants: nitrogen, phosphorus and potassium. The nitrogen in fertilizer generally presents the greatest risk of burn potential, according to the Clemson Cooperative Extension. Although inorganic fertilizers are typically associated with fertilizer burn, nitrogen from organic sources can also burn plants if overapplied.
When added to the soil, fertilizers form salts, which draw water out of plants. Rapid dehydration causes leaves to wilt and turn brown, appearing burned. The salt index compares fertilizers to the salt content of sodium nitrate, according to Michigan State University Extension. Fertilizers with a higher salt index also have a greater burn potential because they pull more water out of the plant.
Although all nitrogen fertilizers have the potential to burn plants, the risk is higher with some than with others. Organic fertilizers tend to burn less easily than inorganic fertilizers. Likewise, slow-release fertilizers won't shock plants with a sudden spike in salts in the soil around their roots and are also less likely to burn.
However, following the instructions on the packaging is the best way to prevent fertilizer burn. Don't overapply fertilizer--it is definitely an instance where you can provide too much of a good thing. When applying lawn fertilizer, the Clemson Cooperative Extension suggests applying it during cool weather and when the grass is completely dry. Water the lawn immediately after fertilizing. When applying fertilizer to vegetable or ornamental plants, avoid applications that bring the fertilizer into contact with parts of the plant. Instead, work the correct amount of fertilizer into the soil around the plant.
In addition to the potential for harm to plants in your lawn and garden, overusing fertilizer has the potential to harm plants and animals far from your home. Fertilizer leaches into groundwater and runs off to pollute lakes and streams, causing aquatic dead zones and health risks due to tainted water, according to North Carolina State University.