The best time to seed a lawn in Minnesota is late summer (mid-August to mid-September) due to favorable conditions for germination and growth. In addition, fewer weed seeds are germinating that might compete with the grass seedlings. Lastly, there is ample time for the plants to become well established before winter. Seeding can also be done in early spring. However, weeds and high summer temperatures often reduce the chance of success. If a turf-type tall fescue is being considered for a lawn, the best time for seeding that grass in Minnesota is in the spring (late April to mid-June). U of MN research has shown much better success with winter survival when turf-type tall fescues are seeded in the spring rather than late summer.
Most annual weeds that compete with new grass seedlings germinate in spring. Only the selective preemergent herbicide siduron, (trade name Tupersan), may be used on newly seeded lawns. It will help reduce problems with crabgrass competition while the newly seeded area is getting established. In addition, the short growth period in spring allows less time to develop a root system to survive the summer heat stresses. A newer herbicide available to the commercial lawn care industry is quinclorac (trade name Drive) can also be used close to the time of seeding. It is a postemergence herbicide that will help control both annual grass and broadleaf weeds that may have germinated or started to grow during the lawn grow-in process. How close to the time of seeding it can be used will depend on the specific grass species used either separately or in a mix. As always, applicators should follow label directions exactly - it's the law.
Germination among the different cool season lawn grasses is quite variable. For example, Kentucky bluegrasses can take 14 to 28 days to germinate while perennial ryegrasses will germinate in as little as 5 to 7 days. The fine-leaved fescues generally require 14 to 21 days to germinate. Thus, perennial ryegrass, like annual ryegrass, can seriously compete with the Kentucky bluegrasses and fine-leaved fescues. This can significantly reduce the amount of these two types of grasses in the established lawn. To help reduce that impact, mowing of a newly seeded area should begin when the perennial ryegrass reaches the desired height rather than waiting for the slower germinating grasses to reach that same height. In this way, the perennial ryegrass won't overtop the slower germinating grasses potentially killing them due to excessive shading and hence reduce their presence in the final stand. It should be noted that summer germination times are usually those toward the lower end due to warmer soil temperatures while the longer times are more typical of spring sowings.
Proceed to Dormant Seeding.