The first week of September may be the most critical week of your entire lawn-keeping year.
So, take note. The work you do — or don’t — during the next eight or 10 days could have a serious impact on the quality of your turfgrass for many months to come.
Applications of pre-emergent weedkillers must be made no later than the first week of September. Year after year, I’ve spent a lot of time imparting this message to North Texas gardeners, but there are always folks who simply don’t believe it and get left behind. So, bear with me while I present the hard and fast facts.
Read through them a couple of times. Please. Your lawn will be glad you did.
The basics: what pre-emergents do
▪ “Pre-emergent” products are intended to stop germination of seeds before they emerge (sprout) from the soil.
▪ Pre-emergent weedkillers are not effective on perennial weeds such as nutsedge, dallisgrass and Johnsongrass — only on annual weeds that come up from seed.
▪ We have warm-season weeds such as crabgrass, grassburs and spurge. Those germinate in spring through early summer and grow during the hot weather. They are visible now. Application times for pre-emergent control of warm-season weeds would be (for Fort Worth and surroundings) the first week of March and repeated the first week of June.
Fall and winter weeds
▪ We also have cool-season weeds that germinate in early fall and become unsightly over the winter and spring. They are about ready to gear up, meaning that this is the time (now through the first week of September) to apply a pre-emergent to prevent their germination.
▪ Cool-season weeds you can prevent with this early September application include (grassy weeds) annual bluegrass, rescuegrass and ryegrass, and (broadleafed weeds) henbit, chickweed, dandelions and clover.
Reading the labels
▪ Pre-emergent products to prevent grassy weeds include Team, Dimension, Halts and Balan. You will need a Gallery product to prevent germination of broadleafed weeds.
▪ Many of the national chain stores either don’t carry these products for fall application, or they will try to convince you that the timing is wrong — that they should be applied later (once their ill-timed shipments arrive). I’ll stand by my guns: first week of September.
▪ Local independent retail garden centers usually have the best selection of products as well as staff on hand with enough knowledge to make recommedations.
If you want to prevent germination of both grassy and broadleafed weeds, you will have to make two passes over your lawn.
▪ Don’t be surprised if the products that are offered for sale say “crabgrass preventer” or something similar on their labels. Most of the sales for these products come in the spring (many people haven’t learned about the importance of this fall treatment yet).
However, the active ingredients are the same, so it’s fine to buy something labeled for crabgrass, even knowing that that’s not the weed you’re going after with your September application.
Treating for grassy and broadleafed weeds
▪ If you want to prevent germination of both grassy and broadleafed weeds, you will have to make two passes over your lawn. Do not try to mix the products in your fertilizer spreader. Their granule sizes will be different, and you will end up with terrible results.
▪ These materials are safe on any type of lawn grass, and they will not harm trees and shrubs. Most are not labeled for use in vegetable gardens. They are primarily intended for turf applications.
▪ These materials are almost all granular. Mow first. Apply them, then water your lawn modestly to spread them across the soil surface. By the time you’re ready to mow again, they will have soaked into the top quarter-inch of soil to do their job.
Mature lawns and organic alternatives
▪ Pre-emergent weedkillers should only be applied to mature lawns. Most manufacturers use the warning that they should not be applied until a lawn has been through its first winter. So any seed or sod that was planted this year would not be cleared for treatment until next spring or next September, depending on the need.
▪ People ask about organic alternatives, specifically corn gluten meal. I do not feel it is at all effective and it’s expensive to boot. If you care to access it, there is great information from Extension horticulturist Linda Chalker-Scott of Washington State University at http://bit.ly/1MOyYV6.
Ryegrass and bluegrass
▪ If you do intend to overseed your lawn with ryegrass this winter, no, you should not apply a pre-emergent weedkiller. Plant your ryegrass in early September and it will conceal the presence of most of the weeds.
As a side note, “perennial rye” is by far the better choice to overseed. It’s finer textured, it germinates more uniformly, and it’s more easily maintained. It is not perennial in our climate. It, too, will disappear once it gets hot. But for the fall, winter and most of the spring, it will give you a beautifully green lawn.
▪ If you have traditionally had a serious problem with grassy weeds such as the annoying little annual bluegrass (Poa annua) in your lawn, application of the pre-emergent in early September is your only chance to stop it. We have no product that will selectively kill it in an established lawn without killing the lawn.
Once temperatures fall in early September and the annual bluegrass begins its germination, you’ll have no other recourse for an entire year.
Neil Sperry publishes Gardens magazine and hosts “Texas Gardening” from 8 to 10 a.m. Sundays on WBAP/820 AM. Reach him during those hours at 800-288-9227. Online: http://neilsperry.com.