All of a sudden, you find your lawn overall is turning more and more yellow-green rather than the deep green of a couple of weeks ago. Provided a mass pest or disease infestation hasn't occurred, chances are your lawn is lacking both proper soil nutrition and proper watering. Soils depleted of nitrogen, in particular, will turn yellow prematurely, but a lack of iron can also lead to yellowing. Insufficient watering in summer's heat can also cause grasses to fall into premature dormancy by yellowing. Seasonal temperatures can also cause grasses to yellow, such as cold temperatures on warm-season grasses like bahia grass or excessive heat on cool-season grasses like fescue or bluegrass.
Measure the area of your lawn area that is yellowing using a tape measure or pacing it off with your feet, toe to tip, or in walking steps. Multiply the length by the width of the area to determine the square footage requiring a fertilizer treatment.
Buy a quality, granular turf grass fertilizer. Choose one that is rich in nitrogen and is primarily slow-release. Nitrogen is the first number in the three-part ratio listed on fertilizers. For example, a high-nitrogen fertilizer for lawns may look like 24-8-16.
Note the weight of the fertilizer, for example 40 lbs., and the ratio number of nitrogen which is the first number in the three-part ratio on the bag's front. In the previous example, it was 24-8-16. The number 24 reveals the percentage by weight of nitrogen in the bag. Write down .24 and multiply it by the bag's total weight, 40 lbs. Use a calculator if necessary. The resulting number is 9.6 (the bag contains 9.6 lbs of nitrogen by weight).
Use the general guideline that only 1 lb. of nitrogen must be applied to every 1,000 square feet of lawn, never more, especially in the heat of midsummer. Continuing with the example from Step 3, divide 1 by 9.6 to get the answer of .104. Multiply .104 by the weight of the fertilizer bag 40 lbs., and the product 4.16 reveals that you must spread 4.16 lbs. of the fertilizer granules over a 1,000-square-foot area.
Modify the amount of the 4.16 lbs. per 1,000 square feet amount if your lawn area is not exactly 1,000 square feet. For example, if your area to fertilize is 250 square feet, multiply 4.16 pounds by .25; if your area is 1,500 square feet, multiply 4.16 lbs. by 1.5. This reveals the total weight of fertilizer granules you must weigh out and then evenly scatter across the yellow lawn area.
Weigh out the appropriate amount of fertilizer from the bag into a plastic bucket on a small household scale. Evenly broadcast it by hand or using a fertilizer-scattering device across the yellow lawn area.
Follow product label directions for recommendations on time of day for applications, need for gloves of other equipment and the need for watering after application. Use either an in-ground irrigation system or a garden hose and sprinkler head to water the lawn after you scatter the fertilizer.
Monitor the response of the treated lawn area over the next seven to 14 days. Water to keep the soil moist and allow the leaf blades to grow without a harsh, short mowing during this reaction period.