Lawn care calendar for Minnesota: when to fertilize and seed

Phases are the university calendar: the best time first, a second-best time where it lists one. Local weather moves them a week or two.

Which grasses grow where in Minnesota

Minnesota lawns are Kentucky bluegrass, fine fescues, turf-type tall fescue and perennial ryegrass in various blends. The university groups five fine fescues together: strong creeping red, slender creeping red, Chewings, hard and sheep. A mix of strong creeping red, Chewings and hard fescue works for home lawns; hard fescue is the most drought tolerant, and creeping red and Chewings tolerate the most tree shade.

Fine fescues need less water, mowing and fertilizer than bluegrass and are mowed at 2.5 to 4 inches, with most of their nitrogen applied in fall. Tall fescue is a little coarser than bluegrass, slow to green up in spring, and the university notes that spring seedings of it survive the first winter better than fall ones.

Frost dates from NOAA

Dates are the NOAA 1991-2020 normals for the last spring and first fall 32 F freeze at 50% probability. At Minneapolis-St. Paul International Airport the last spring frost averages April 23 and the first fall frost October 18. At Rochester International Airport the dates are April 30 and October 6. At Duluth they are May 13 and October 1.

Counting the days between them, the Twin Cities average about 178 frost-free days and Duluth about 141 (our arithmetic).

Spring

Mowing starts in the last week of April. The university says not to add fertilizer too early, because it pushes growth when the grass should still be slow, and gives May through late June as the spring feeding window. Crabgrass preventer goes down from mid-April to mid-May, before crabgrass comes up, with the soil near 55 F; sprays against small crabgrass work from mid-May to early July.

Keeping the mower at 3 inches or higher shades the soil and lowers crabgrass germination. Aeration from late April through May is the spring option, with the main aeration in late summer and early fall.

Summer

Mid-summer feeding can cause lasting damage, so the university schedules none in July. Cool-season roots can be hurt when soil is above 85 F. The university suggests watering once a week or less with enough water to wet the soil 6 inches down, which can be as little as half an inch on some soils, and watering in the morning.

Kentucky bluegrass starts browning after about a week without water and recovers when rain returns. Tall and fine fescues can stay green for at least 28 days without water. In a drought, the university advises postponing mowing until moisture returns and keeping traffic off the lawn, since mower traffic can scar dormant grass permanently.

Fall

Early August to late September is the best seeding time, and fertilizing continues from early August through mid-October. Aerating runs from mid-August through mid-October and dethatching from mid-August through September. Broadleaf weed killer works best from September through late October.

The university's fertilizing guide sets nitrogen by how you care for the lawn and how much organic matter the soil holds. A watered lawn with clippings returned gets about 2.5 pounds a year on medium organic matter, in August, September and May or June. A lawn with some watering and clippings returned gets 1.5 pounds, in September and May or June. An unwatered lawn gets 1 pound in September. No single application should exceed 1 pound per 1,000 square feet.

The phosphorus law

Minnesota Statute 18C.60 says nobody may apply fertilizer containing phosphorus to turf anywhere in the state, with three exceptions. A soil, tissue or other approved test done within the last three years can show too little phosphorus for healthy turf. The property can be new turf from seed or sod, in its first growing season only. Licensed golf course managers have a third carve-out. Any permitted application has to stay within the University of Minnesota rates.

Extension adds that many Midwestern soils already hold plenty of phosphorus, established lawns respond little to more, and new turf may benefit because phosphorus moves slowly in soil. The middle number on the bag is the phosphorus.

The bag math

The extension rates are in pounds of nitrogen per 1,000 square feet, but a bag lists a percentage. The lawn fertilizer calculator on this site turns the first number on the label and your lawn size into pounds of product, so a 1 pound application takes the same effort every time.