Renovating Cool-Season Lawns

Much of Virginia dealt with moderate to severe drought for most of the summer and in many places the drought continues into the fall. Some cool-season lawns have been dormant for weeks now and until they receive ample rain, one won’t be able to distinguish dormant turf from dead. This weather pattern has convinced numerous homeowners from Richmond and to the east that perhaps warm-season grasses (bermudagrass, zoysiagrass, centipedegrass, and St. Augustinegrass) really do have a place in a Virginia lawn. However, even with their superior tolerance to heat and drought, some of the warm-season grasses have shown signs of moisture stress and have entered dormancy themselves.  Still, the poorest quality warm-season lawns I have seen this year are far superior to any non-irrigated cool-season lawns that I have been asked to examine. Weeks of record heat and extended drought have taken their toll on much of our landscape, and the effects on all of our plant materials (lawns, trees, shrubs, and other ornamentals alike) will probably show the effects of this summer for months to come.

What should we be considering regarding the renovation of cool-season lawns when (if?!) the weather pattern finally breaks? Here are some ideas to consider as you plot your recovery plan.

How much renovation is required? If you have just a few spots around the lawn, concentrate solely on them, using a heavy garden rake to loosen the dead plant debris and disturb the soil surface prior to seeding. While you won’t likely be calibrating a spreader for such a small area to seed, don’t bury the soil in seed. Too heavy of a planting rate exaggerates disease pressure for the new seedlings. Apply fertilizer according to a standard fall fertility program (we usually recommend the “SON program”… up to 1 lb N/1000 sq ft per month of Sept., Oct., and Nov…. we’ll say a little more about this later) and keep any new seeding moist but not saturated. Don’t forget that sod in these problem areas is also a good option! If significant lawn renovation seems to be a problem for you just about every year (or you are just ready for a change in cool-season lawn grass), then perhaps the low quality lawn you have now justifies this as an opportunity to switch to a better adapted grass or variety for your situation. Most likely the loss of turf this year has been due to the heat and drought, but it would be a good idea to check your soil by testing if you have not done so in the past three years. In my mind, if you consistently lose more than 50% of your lawn due to summer stress, then there must be an issue in your grass selection. For those of you in the southern Piedmont and Tidewater regions, it might be time to walk away from the cool-season grass and plant a warm-season turf next spring (or sod it now—that will still work). Consider starting over again by applying a non-selective herbicide (something like glyphosate or glufosinate) to control all the vegetation in the lawn and plan on seeding or sodding the entire area. It will be beneficial to perform some type of soil surface disruption (perhaps a vertical mowing or a core aeration event) to improve soil to seed contact, but complete tillage is usually not necessary for seeding if you are satisfied with the slope of your lawn. For sod installations, a light tillage to remove the organic layer on the surface is desirable. Also consider that moderate to extensive renovation affords you the opportunity to make improvements in any surface or sub-surface drainage issues, and it is a great time to install an in-ground irrigation system or wiring for more outdoor lighting. You can find plenty of details on preparation and establishment practices in the attached VCE publication “Fall Lawn Care”.

We mentioned core aeration as part of a renovation program. This is a great tool to improve turf establishment, but remember that the soil must be reasonably moist to aerate, otherwise your coring machine will simply bounce around the surface and probably break a large percentage of the coring tines. Is there an easy way to know when a soil needs aeration? Give it the “screwdriver” test—if you can push the business end of a flat-head or Phillips-head screwdriver 3 inches into a moist soil without undue force (no jabbing, hammering etc.), then coring is likely not required. If my soil passes the screwdriver test, can it still benefit from a core aeration event? Sure. Coring stimulates soil microbial populations, organic matter decomposition, and the oxygen further enhances the health and function of your turf root system. It also is a great soil preparation technique for moving lime, fertilizer, seed, or compost applications into the soil.

What about fall fertility ideas for a renovation situation?  There is no point in applying fertilizer to a dormant lawn. It presents a possible environmental hazard and is a waste of money. So if you still haven’t received significant rain to promote turf recovery, don’t apply fertilizer just because of what the calendar says. The “SON” timing program very likely won’t work for cool-season turfgrasses this year. We might need to push our first fall application back 2-4 weeks from normal until we get some active turf growth. But when your turf does show some signs of life following fall rains, help it out by feeding it this fall. Your lawn will benefit not only now, but next spring as well.

What about weed control? For many of us, about the only thing that has done well in our cool-season lawns this summer has been crabgrass. There is still an opportunity to control crabgrass with the herbicide quinclorac (trade name, Drive), a product that can be used by homeowners that has very little impact on any fall seedings you might want to make (it is a specialty product that you likely won’t find at a big-box retailer). However, is its application justified? For most of us, I am going to say “no”. Remember, crabgrass is going to die with the first killing frost. I’d rather core cultivate and apply more desirable grass seed to fill in the voids that will be left behind by the dying crabgrass. Are you still going to have some weeds? Most definitely -- remember that weeds beget weeds! What I mean is that as one weed dies, it usually creates the space for another one to move in. This cycle occurs every year with the fall decline of crabgrass, goosegrass, foxtail, etc. only to be replaced in your lawn by annual bluegrass (Poa annua), chickweed, henbit, etc. Then it starts all over again next spring with the death of the winter annuals followed by the emergence of all the summer annuals. The best way to manage weeds in your lawn is through the establishment and maintenance of a dense turf that is achieved by proper seeding, fertility, mowing, etc. You can help break the cycle with chemistry by choosing the appropriate herbicides. As just mentioned, your choices in herbicides for fall applications can be severely restricted if you are going to seed. If you have a reasonably thick turf canopy that you can restore primarily through sound fertility, irrigation, and mowing programs, then you might want to use a standard PRE herbicide (same as for spring crabgrass treatments) for winter annual weed control. Or you might choose to wait and see just how many winter weeds emerge in your lawn and plan on treating them in a few weeks when they are still very young and actively growing. Again, just be sure that if you are doing any fall seeding that the chemistry you choose to use is safe for new seedlings. Complete information on what is available in pest control products in the lawn and landscape can be found in the Virginia Tech Pest Management Guide (just type in PMG on the Virginia Tech home page, www.vt.edu).

I hope this podcast has provided you the information required to restore your lawn to a level that enhances the appearance and functionality of your landscape. For further information on lawn care in your area, be sure to contact your local Virginia Cooperative Extension office.