How Soon Can I Fertilize a Lawn After Already Fertilizing?

Nutrients For Lawn Grass

• While plants produce their own food by the process of photosynthesis, the elements they use as building blocks for proteins, carbohydrates and other compounds are absorbed from the soil by the roots. The main nutrients commonly needed in larger quantities than are found naturally are nitrogen, phosphorus and potassium, the macro-nutrients expressed as three numbers on a bag of fertilizer, the NPK ratio. Nitrogen is the most important for lawns, the one that promotes the growth of green leaves and the one that is most often in short supply. Phosphorus and potassium contribute to the growth of strong stems and roots.

Choosing A Fertilizer

• First, have your soil tested professionally to determine the amount of phosphorus and potassium you need to add. These nutrients are fairly stable in the soil and the results of your test will be valid for several years. The ideal time to add phosphorus and potassium is before seeding or sodding but later applications can also be useful. Choose a fertilizer with a low or high amount of these elements based on your soil test. The amount of nitrogen to apply depends on both your type of grass and the level of maintenance you desire. More nitrogen means more watering and mowing. An excessive amount of nitrogen or improper application, however, can cause fertilizer burn, a browning of the leaves.

Timing the Applications

• A high maintenance lawn, one composed of vigorous improved Kentucky bluegrass or improved perennial ryegrass and that is watered during hot spells without rain, will need three to four pounds of nitrogen per 1,000 square feet each year, spread in three to five separate applications. These can be one month apart, but late summer or fall is better than spring if you choose to put them on so close together. Fall fertilizing will give you a strong root system that supports steady growth the next year while spring applications weaken the grass by pushing out excessive new growth.

Proper Fertilizing Techniques

• Be sure the ground is moist but the grass leaves are dry before applying granular fertilizer to avoid burning. Water afterward to wash the granules from the leaves. Remove any fertilizer from your driveway and walkways so it won't be washed into the storm sewer and waterways, causing pollution. Leave grass clippings on the lawn to dry and work their way down into the soil. As much as 25 percent of your lawn's nutrient needs can be met by decayed clippings.