By Carl Wilson, Colorado State University Cooperative Extension
The arrival of cooler weather in September may signal the perfect time to tackle renovating thin lawns. Cool weather is optimum for growth of cool season grasses, such as bluegrass, and the lower temperatures slow drying of seeded areas, leading to better germination.
In addition to cool temperatures, water is required on a daily basis for successful seed germination. If water restrictions limit your ability to water several times daily, seeding is not an option and sodding should then be considered. In cool weather, sod requires watering once every two to three days until its established, a process that takes 2 - 3 weeks. If water restrictions in your area include an early cutoff date for lawn watering, the chances of winter survival for newly seeded or sodded lawns are reduced.
In addition to lawns thinned by drought, other candidates for renovation include lawns plagued by winterkill and those suffering from too much shade and thus requiring a change to a more shade tolerant turf type.
Consider three possibilities in deciding whether to renovate or totally replace the lawn.
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 or slit seed machine (these can be rented at many garden or home centers) 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.
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. Hand pull weeds if needed. Begin mowing when the grass is 3 inches tall and mow to a height of between 2 to 3 inches.
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
If lawns are sufficiently thin and weedy to require replacement, sodding is an option to consider as an alternative to seeding the entire area. Before laying sod, consider whether the weeds growing on the site will be a problem. Tenacious perennial weeds such as thistle and bindweed can punch through and prosper in new sod. Take the time to repeatedly treat and eliminate these weeds with systemic glyphosate type herbicides to kill the roots before laying sod. Heavy weed infestations may require a fall weed treatment program to be followed by later sodding.
bluegrass sod may be laid in all but the coldest months of the year. In
advantage of the complete replacement to prepare the soil thoroughly. Poor soil conditions
are the primary cause of lawn failure in
Prepare soils by thoroughly mixing in a minimum of 4 cubic yards of organic soil amendment per 1,000 square feet of soil. Use amendments such as sphagnum peat, compost or well-rotted manure. Mix this in to the top 6 inches of soil. A better option in tight clay soils is to double the amount of soil amendment and incorporate it at a 12-inch depth using special deep ripping equipment. See the fact sheet on Choosing a Soil Amendment or request it from the Colorado State University Cooperative Extension office in your county.
After installation water the sod thoroughly and repeat every 2 to 3 days in cooler weather (more frequently in warm weather) for 2 3 weeks. Check moisture in the sod and soil beneath before watering to avoid under or over-watering. Sod should knit, or begin to root, into the site soil within 2 weeks. Gradually cut back on watering after this by increasing the number of days between applications. Also, plan to winter water on a monthly basis during dry winters.
More information on seeding, sodding and renovating lawns can be found on the Colorado State University turf Web page Newlawns.
While renovation or replacement work in September will add to your list of fall chores, the reward next spring of a lush and healthy lawn will make it all worthwhile.
Photo: Judy Sedbrook
© CSU/Denver County Extension Master Gardener 2010
888 E. Iliff Avenue, Denver, CO 80210
Date last revised: 01/05/2010