Healthy lawns are not only beautiful, they are beneficial. They filter rainwater runoff and conserve topsoil that can dry up and blow away if not covered with grasses. Fertilizer is used to increase the health of lawn grasses. The effects of applying fertilizer to a lawn can be both positive and negative.
Increase in Growth Levels
When fertilizer is applied in the correct amounts at the right time, it benefits the growth of the grass by supplying important nutrients to the plant system--such as nitrogen and phosphorous. Applying the correct amount of fertilizer that contains nitrogen gives the grass a dark green color and faster top growth. Phosphorous helps the grass grow an extensive and healthy root system.
Ability to Handle Environmental Stress and Disease
Lawn fertilizer often contains potassium. Potassium helps the grass by strengthening the cellular walls that make up the grass leaves and roots. This helps the plant remain healthy during periods of extreme heat and cold. Also, potassium increases the grass's ability to resist some diseases and recover after being attacked by damaging insects.
Leaf Burn and Plant Damage
An over-application of fertilizer causes a variety of problems. Some of those problems are leaf burn, decrease in plant growth, susceptibility to disease and environmental stress, and sometimes death of the lawn. The risk for damage is higher when fertilizers containing high levels of nitrogen or phosphorous are misapplied. Always obtain a soil test before applying fertilizer on the lawn so you do not over- or under-apply the nutrients your lawn needs. Obtain a soil test by contacting you local County Agricultural Extension Office.
Stream and River Pollution
Over-application of fertilizers is a problem when it runs off the lawn and enters streams and other waterways. Nearly all water entering a storm drain after it runs off a lawn eventually makes it to a waterway. As it carries the excess nitrogen and phosphorous from the fertilizer to the waterway, it causes an increase in algae levels. After the excess algae growth, commonly called an algae "bloom," reaches an unsustainable level, it dies and consumes large amounts of oxygen as it decays. The decrease in oxygen in the waterways leads to the death of fish and other aquatic life. This is another reason a soil test is important, so fertilizer is not applied indiscriminately.