John R. Street
Susan K. White
A good lawn needs adequate nutrients for good growth. Lawns need regular fertilization to keep the grass growing and weeds out. The best way to determine a fertilization program for your lawn is to take a soil test. Your county Extension agent will advise you on how to take a soil sample and how to send it to the soil testing laboratory. The report from your sample will be returned by mail and will tell you what mineral elements your lawn needs.
Grass should be fertilized with nitrogen, phosphorus and potassium. Choose a fertilizer with the proper ratio of each of the nutrients to correspond to the soil test results. The fertilizer label must state the percentage by weight of nitrogen, phosphorus and potassium in that order. A 20-10-10 fertilizer has the mineral elements in the ratio of two parts of nitrogen, one part of phosphorus and one part of potassium (2-1-1), as does a 10-5-5. The difference is that weight for weight the 10-5-5 contains half as much fertilizer value as the 20-10-10, and twice as much would have to be used for the same results.
A 100-pound bag of 10-5-5 fertilizer contains 10 pounds of actual nitrogen (100 lb x 10 percent nitrogen = 10 lb), five pounds of actual phosphorus (100 lb x 5 percent phosphorus = 5 lb), and five pounds of actual potassium (100 lb x 5 percent potassium = 5 lb). The amount of nutrients in any other fertilizer can be determined in the same way. The amount of fertilizer product to apply is based on the percentage of nitrogen, the first number in the analysis (Table 1).
Generally, a 3-1-2, 4-1-2 or 5-1-2 ratio is considered best for Ohio lawns. The ratio need not be exactly 3-1-2, 4-1-2 or 5-1-2. For example, 24-6-6 analysis approaches a 4-1-2 ratio, and a 10-3-7 grade is close to a 3-1-2 ratio. Substitutions of this type can be made without concern.
How do you choose between products with the same nutrient content? The big choice is between fast and slow release of the nitrogen fraction. The percentage of the total nitrogen that is water insoluble and that which is water soluble usually is listed on the fertilizer bag. In the water soluble form the nitrogen is available quickly, and in the insoluble form it is available slowly.
A good turf fertilizer contains some of each kind of nitrogen. The slow release portion provides nitrogen over a period of time but is not available to the plant during cool weather. The soluble fraction, or fast release, will provide nitrogen almost immediately after application and during cool weather. Something approaching 30 percent to 50 percent insoluble or slow release (time released) nitrogen is suggested.
University research has shown that fall (August or September) and late fall (October, November or December) fertilization is ideal for home lawns. Fertilization during these times will benefit lawns more than any other practice. Most homeowners place too much emphasis on spring and summer fertilization. Some fertilizer is needed during the spring and summer, however, over-application of fertilizer at these times can cause disease and other problems and result in "summer lawn nightmares."
Disease and weed problems are usually less severe when fall and late fall fertilization are practiced. Heat and drought tolerance are usually better, thus enhancing summer lawn quality. Finally, the grass plant produces more root mass and a deeper root system, resulting in an overall healthier plant.
Lawns need to be fertilized periodically (several times) throughout the growing season. Fertilizations (feeding) should be made at eight to ten week intervals throughout the growing season. A general fertilization schedule for homeowners interested in a moderate to high-quality lawn is provided below.
Any fertilizer may burn the turf if applied improperly. Fast release nitrogen is more likely to burn than slow release forms. To avoid burn: 1) Do not apply more than 1 1/2 pounds of actual nitrogen per 1,000 square feet at one time; 2) Spread uniformly; 3) Do not overlap or spill fertilizer; 4) Apply fertilizer only when foliage is dry; 5) Water after application. Pulverized materials are more likely to burn than pelleted or granulated materials.
Lime should be applied only when a soil test indicates a need for it. Excessive amounts of lime in the soil may be detrimental to the production of good turf. When a soil test is made, apply the amount recommended. Liming will not reduce the need for fertilizing. The presence of moss in the lawn does not necessarily indicate a need for lime.
It is advisable to return grass clippings to the lawn because they
are a valuable source of nutrients. Research has shown that when
clippings are removed, a third more nitrogen fertilizer was necessary
to maintain the same color and density as areas where clippings were
returned. Furthermore, and contrary to popular belief, grass
clippings do not contribute to thatch accumulation if the turf is
maintained at its recommended cutting height and not more than a
third of the leaf surface is removed at one mowing.
|(Pounds fertilizer per 1,000 sq. ft.)|
|Examples of some fertilizer Grades/Analyses Available*||April May||June July||August September||Oct. Nov.** Dec.|
|10-6-4||5||5 to 10||10||10 to 20|
|15-3-3, 15-5-10||3||3 to 7||7||7 to 13|
|19-3-3, 19-5-10, 20-4-8||3||3 to 5||5||5 to 10|
|24-4-8, 24-4-12||2||2 to 4||4||4 to 8|
|28-4-12, 28-3-3, 29-3-5||2||2 to 4||4||4 to 7|
|34-5-5, 34-5-10||2||2 to 3||3||3 to 6|
|*Fertilizer ratios of 3-1-2 to 5-1-2 preferred|
|**Earlier date for northern Ohio and later date for southern Ohio|
All educational programs conducted by Ohio State University Extension are available to clientele on a nondiscriminatory basis without regard to race, color, creed, religion, sexual orientation, national origin, gender, age, disability or Vietnam-era veteran status.
Keith L. Smith, Associate Vice President for Ag. Adm. and Director, OSU Extension.
TDD No. 800-589-8292 (Ohio only) or 614-292-6181