Thursday, August 23, 2018

Renovating the Lawn in Fall

Photo by Donna Duffy
Does your lawn have dead spots or thinning? Do you have sections that just aren’t thriving? Once you've ruled out irrigation problems, consider renovation of the turf - and fall is the perfect time to do it. Cool weather is optimum for growth of cool season grasses, and lower temperatures slow the drying of seeded areas, leading to better germination.  Following are tips for lawn renovation from Carl Wilson, CSU Horticulturist.

Photo courtesy

Consider three possibilities in deciding whether to renovate or totally replace the lawn.
  • Slightly thin lawns with few weeds will greatly benefit from late season fertilization, the most important fertilizer application of the year. Renovation likely is not needed in this case. In Jefferson County, fertilize in late September or early October while the grass remains green. This fertilization will increase winter survival, promote early spring green up and increase lawn density in the spring. At least one irrigation following fertiliztion is desirable.
  • If fifty percent of the lawn is grass, renovation through overseeding the existing turf may be feasible. Seed can be of the same grass species or a compatible one.
  • In cases with very thin or weed infested turf, complete replacement may be necessary. 
Remove weeds before overseeding, photo by Donna Duffy

Renovation procedure
The renovation procedure will vary with the amount and type of weeds. Annual or easy to kill broadleaf weeds can be selectively removed from remaining grass by hand or with a 2,4-D, dandelion-type herbicide. Renovation overseeding can follow after weeds have died. Allow 2 to 4 weeks after using 2,4-D herbicides before seeding (be sure to read and follow label directions.)  Broadleaf weeds such as thistle or bindweed will likely require several applications of an herbicide specific for hard-to-kill broadleaf weeds. In this case, consider fall as the weed control period in preparation for spring seeding.

Seed will only germinate where it contacts soil. Don't simply overseed an unprepared lawn surface of grass leaves or thatch. One method of preparation involves using a core aerator to expose the soil and help create good seed contact. Seed falls in the holes where it is protected from drying and is more likely to germinate.

Core aeration, photo courtesy

Frequent, light waterings (as many as two to four times a day), are necessary to germinate seed. The frequency will depend on daily high temperatures and the amount of sun and wind. Waterings may be required for only one or two minutes per application.   The purpose of these short but frequent waterings is to keep the top 1/4 inch of soil moist so germinating seeds don't dry out and die. Germination may take two weeks depending on temperatures and grass species.

Once seed has germinated, gradually cut back on the frequency of watering to twice weekly. Weed seeds are likely to germinate, but don't spray herbicides that can injure young grass until the area is mowed 5-6 times. Begin mowing when the grass is 3 inches tall and mow to a height of between 2 to 3 inches.

Although seeded areas may appear sparse at first, density will increase as grass blades grow and fill out. Note that seeding should be done by the end of September on the Front Range in order to allow time for grass establishment before cold weather sets in. New grass will benefit from winter watering in dry winters.

For more information, check out CSU Extension’s publications, Fall Lawn Renovation Offers a Jump on Spring. and Renovating the Home Lawn.