When to fertilize depends on if your lawn is made up of cool season grass or warm season grass. Cool season grasses (tall and fine fescues, Kentucky bluegrass, perennial ryegrass) look best when the weather is cooler: fall, winter and spring. In times of hot, dry weather they can go dormant. Warm season grasses (Bermuda, zoysia, centipedegrass) thrive in hot summer conditions, but go semi- to completely dormant in winter.
For cool season grasses, chemical fertilizer applications should stop between mid-March and mid-September, the ideal time of application being October, November and February. Warm season grasses should be fertilized from the time of green up in spring through September, with supplemental winter feeding if overseeded with a cool season grass.
But wait -- you've seen lawn services fertilize cool season lawns in summer. Why shouldn't you? Terry Fiks, manager of New Garden Select explains it like this: “Our process is similar to spoon feeding. (We use) enough N (nitrogen) to keep color without stimulating an abundance of new growth and promoting disease. I think it would be safe to say that many homeowners do not know how much N they are putting out and many believe a little is good so more is better.”
If you miss the window of opportunity in early spring, what options do you have to keep your lawn green in summer? One source of nitrogen that is often overlooked is the lawn clippings themselves. When left on the lawn to decompose, they return nitrogen to the soil, up to 25% of a lawn’s nitrogen needs. This requires frequent enough mowing that the clippings are not excessive. (Remember, nothing will revive color in a dormant lawn but cooler temperatures and irrigation.)
Another option is to apply lime to the lawn, which can be done any time. Many nutrients are easier for grass to take from the soil and use at a pH range of 6.0 to 7.0. As you can see on the chart to the right, any nitrogen in the soil will be more available at 6.0-7.0 range than 5.0-6.0. If a soil test shows your lawn’s pH dropping below 6.0, adding a quick acting calcium product like Turf Turbo from Bonide may give you some greening without excessive growth and risk of disease.
Finally, if you really feel need to feed your lawn in summer, consider using organic products formulated for lawns. With lower (yet still effective) levels of nitrogen in slow release form, you can get nice greening safely. Organics products work best when used as part of a year round organic program.