Lawn care calendar for Illinois: when to fertilize and seed

Dates shift with the weather; follow the signs in the text.

Which grasses grow where in Illinois

Illinois lawns are mostly cool-season: Kentucky bluegrass, perennial ryegrass, fine fescues and tall fescue. Illinois Extension also lists mowing heights for bermudagrass, buffalograss and zoysiagrass, which it describes as warm-season grasses growing in the state, but its fertilizing schedule is written for cool-season lawns and that is what most yards follow.

Tall fescue seed goes down at 6 to 9 pounds per 1,000 square feet, Kentucky bluegrass blends at 1 to 3 pounds. Extension suggests splitting the seed in two passes, one east to west and one north to south, and raking it lightly into the soil.

Frost dates from NOAA

Dates are the NOAA 1991-2020 normals for the last spring and first fall 32 F freeze at 50% probability, so about half of years bring frost later in spring or earlier in fall. At Chicago O'Hare International Airport the average last spring frost is April 16 and the average first fall frost is October 28. At Springfield (Abraham Lincoln Capital Airport) the dates are April 14 and October 20. At Carbondale (Southern Illinois Airport) they are April 9 and October 22.

Spring

Spring work is light. Crabgrass seed sprouts once soil stays above 55 to 60 F for 7 to 10 days, so a preventer goes down before that: late April to early May in the north, mid to late April in the middle and early to mid April in the south. In a cold spring, wait until the end of that window.

Illinois Extension asks for about 1 pound of nitrogen per 1,000 square feet in each feeding and about 3 pounds across a season for a lawn in full sun, with half as much in shade. Mow at 2.5 to 3 inches and never remove more than a third of the blade at once.

Summer

Cool-season grass slows down in heat and may go dormant. Extension says watering is optional: about 1 to 1.5 inches a week keeps a lawn green, and a lawn left alone usually recovers when fall brings cooler weather and rain. Pick one approach, because turning a brown lawn green and then letting it rest again drains the plant.

Water early in the day, thoroughly and not often, and keep mowing high. Avoid extra nitrogen as warm weather approaches.

Fall

Fall is the main season. Seed and the big feeding both belong in the window above, and a late-season feeding goes on about a week after the final mowing: late October to early November in the north, November in the middle and late November in the south.

How many feedings you give depends on how dense you want the lawn. One feeding in late summer suits a relaxed lawn, two add a spring feeding, three add the late-season feeding, and four add an early-summer feeding for irrigated lawns.

Illinois Extension and soil testing

Illinois Extension keeps a full lawn guide at extension.illinois.edu/lawns. A soil test tells you the pH and the phosphorus and potassium levels, which nitrogen math cannot, and Illinois soils often hold enough phosphorus that a starter fertilizer is unnecessary.

Illinois Extension says to use labs certified by the Agricultural Laboratory Testing Association, which keeps a list of commercial labs. The Illinois-Indiana Sea Grant Lawn to Lake website also lists labs, and several land-grant universities, including Missouri, Wisconsin, Kansas State, Kentucky and Minnesota, run soil labs.