Fertilizer is a necessity in order to maintain a healthy lawn. There are many factors that go into determining how much fertilizer a lawn will need, including the age of the lawn, the climate and the soil type. Zac Reicher and Clark Throssell, turfgrass specialists at Purdue University, advise that the goal of nitrogen fertilizer is to produce a lawn with moderate growth and good density, not just a bright green color.
A nitrogen fertilizer's job is to provide the right nutrients for a lush and healthy lawn. The nitrogen itself is responsible for the vigorous growth of the grass and the deep, green color. Along with the two other components, phosphorus and potassium, a nitrogen-rich fertilizer will also help to strengthen your lawn, from the roots up, and protect it from disease. The strength of a lawn will also determine how well it survives over the winter, in the colder parts of the country.
Nitrogen fertilizer can be purchased in organic or inorganic varieties. Organic fertilizer must first break down in moist, warm soil, causing this fertilizer to release its nitrogen slowly over an extended period of time. While the results of applying this fertilizer are delayed, there is no risk of burning your grass due to excess nitrogen. The inorganic type is fast-acting and releases its nitrogen the moment water is applied to your lawn. The results, and improvement to your lawn, come much quicker, but with that speed also comes the risk of chemical burn if too much nitrogen is applied.
The amount of nitrogen fertilizer you apply to your lawn is determined by the type of grass and the growing conditions. Fast-growing grass varieties, such as Kentucky bluegrass and turf rye grass, require more applications to meet their nutrient demands. Slow growing grasses, such as fine fescues, require less fertilizer to meet their needs. Grasses growing in shaded areas also require less fertilizer, as they will grow slower without full exposure to the sun.
There has been some resistance to using nitrogen fertilizers, due to the perceived risk of the nitrogen leaching out of the soil or being carried away with ground runoff into local water supplies. This risk is all but eliminated, if proper application techniques are followed. When applied in the proper amounts, to dense turf, the lawn, its root system and thatch absorb all the nitrogen. The key to proper application is to calibrate the spreader to provide a uniform amount of fertilizer over the entire lawn.
The exception to the risk of runoff occurs when nitrogen fertilizers are applied to sandy soils. Sandy soils are, by nature, very porous and require more irrigation in order to provide enough moisture for the lawn. Due to the soil's porosity, and frequent watering, nitrogen fertilizers run a higher risk of being washed away. It is also recommended, no matter which soil type, to only apply nitrogen fertilizers in the fall. Spring and summer applications will result in a lawn with weaker roots but excessive leaf growth. The lawn will need more frequent mowing but will be less resistant to drought or disease.