It’s difficult to wait to fertilize your grass in the spring when everything in the yard is turning green, but you should wait. Greening your lawn early in the spring may make you feel good, but it’s not recommended.
Wisdom about waiting comes from Dr. Peter Landschoot, the extension turfgrass management specialist at Penn State University. He points out that while marketers may call fertilizer “plant food,” the real food that fuels turfgrass is the carbohydrates that grass makes via photosynthesis. Like all green plants, grass uses light energy to convert water and carbon dioxide into carbohydrates.
While fertilizers are nutrients required for plant growth, carbohydrates provide the fuel for growth. Landschoot points out that these self-manufactured carbohydrates are stored in the stem and crown of the grass plant when more are made than are being used. Similar to many other perennial plants, the carbohydrates are stored in the greatest amounts in the fall as plant growth slows. These extra carbohydrates are kept in reserve to help the grass recover when stressed or injured in the coming growing season.
Carbohydrates are used at a high rate in the spring “especially under low mowing heights and high nitrogen fertility,” Landschoot says. That’s why you should not apply nitrogen fertilizer in early spring or mow below the optimum mowing height. (Washington State University recommends a mowing height of 1.25 to 2 inches for Kentucky bluegrass lawns.)
Turf experts at Cornell University also say that fertilizing healthy lawns in early spring “increases top growth (and mowing chores) at the expense of root growth.”
WSU recommends fertilizing your lawn no earlier than May 1 in Eastern Washington, unless nitrogen deficiency is apparent. Exceptions to the May 1 date are lawns that weren’t fertilized the previous fall or lawns that have sustained winter injury. However, fertilizer should not be applied until the soil temperature has warmed to 55 degrees.
It is important to note that the best time of year to fertilize your lawn is Nov. 1–15, when the soil is cooler and the grass plants are recovering from summer heat and growing new roots and tillers.
How much fertilizer should be applied? Kentucky bluegrass, the predominant grass in most local lawns, should receive 2 to 4 pounds of nitrogen per 1,000 square feet of lawn. Use the 2-pound rate, if you have an older lawn or if you are returning your clippings to the lawn with a mulching mower. The 4-pound rate is recommended for young lawns, lawns on sandy soils or lawns where the clippings are being removed. Apply only 1-pound of nitrogen per 1,000 square feet per application.
-- Marianne C. Ophardt is a horticulturist for Washington State University Benton County Extension.