When to Apply Pre Emergent is Google's most searched question about pre-emergent herbicides. Then it is followed by the following: What Month do you put down Pre Emergent? In our North Texas area, When to Apply Pre Emergent in North Texas is the next most chosen search phrase. But before we can answer any of those questions, we need to discard one of the most incorrect perceptions related to the application of pre emergent on Texas lawns: pre-emergent is only applied one time per year.
In 95% of Texas (not counting the far north edge of the panhandle), Louisiana, Mississippi, Alabama, Georgia, Florida, South Carolina, southern New Mexico, southern Arizona, southern Oklahoma, southern Arkansas, and anyplace else growing warm-season grasses in USDA Hardiness Zones 7-13, you apply, then water-in preemergent twice per year, unless you are overseeding with winter ryegrass.
What Month do you put down Pre Emergent in North Texas?
Answer: the first time to apply pre-emergent in North Texas is January 27th - February 20th (or a little later during really cold winters). This pre emergent weed control application is primarily made to stop crabgrass, goosegrass, dalisgrass, and most other broadleaf weeds in the early summer months. Important note: This is not a situation where "the early bird gets the worm." I see some homeowners putting it down on nice North Texas days around New Year's, and I see some unscrupulous (because they are not busy) lawn spray and fertilization companies putting it from Christmas to mid-January. If you put down pre-emergent in North Texas before the end of January, you will probably end up with crabgrass and spurge in June to August, along with throwing away a portion of your chemical cost.
The second time to apply pre-emergent in North Texas is August 27- September 15 (unless you are overseeding with winter ryegrass or a commercial applicator spraying special pre-emergent homeowners can't buy in bags). In our opinion, this application is more important than the known winter application. Why? Because your lawn is brown in the winter. And nothing looks worse than having a dormant, brown lawn full of green weeds. This summer application of pre emergent will stop most ugly winter weeds like poa annua (annual bluegrass), dandelions, chickweed, clover, etc.
How Long After Pre Emergent can I Fertilize or Apply Fungicide?
Some detail-oriented homeowners want to know how long after pre emergent can I fertilize. Answer: you can apply fungicide or fertilizer immediately. Several retail pre-emergents are actually blended in with fertilizer (which we don't choose to use, but nothing is wrong with it). Note: You must pay close attention to the "water in" requirements for the pre emergent vs the fungicide/fertilizer. Some chems require 1/10th of an inch of water, and some require 1/3 inch of water to "set" them. Ensure you follow the label if you want the application to work correctly.
How Long Does Pre Emergent Last in the Soil?
Most name-brand pre-emergents claim to last "up to 6 months." Whether it effectively stops the germination of weed seeds for the entire six months is based on the following factors:
- Most pre emergents have three application levels - minimum, average, and maximum. The thickness of the invisible soil barrier directly applies to how heavily you apply it.
- Did you lightly water it in to get it set into the topsoil layer? Or did you get heavy rain or overwater, which diluted/washed it from various areas in your lawn?
- After you applied the pre emergent, did you do any lawn aeration, topdressing (with sand or organic matter), or deep dethatching? If you did, you ruined most of the pre emergent "barrier."
- Are you using the same pre emergent every year? It is essential to mix up the brand of pre-emergent you use every couple of years. Weeds can become immune to "medicine," just like fungus in grass and viruses and bacteria in humans. That does not mean you need to stop using your favorite pre-emergent forever; rotate in a new pre-emergent herbicide every few years.
How long pre emergent will last is directly attributable to the abovementioned factors.
Will Pre Emergent Kill Grass Seed? Will Grass Seed Grow After Pre Emergent?
Will pre emergent kill grass seed? Will grass seed grow after pre emergent application? Those are intelligent questions.
Answer: pre emergent creates an invisible barrier in the top inch of the soil. The pre emergent herbicide will not technically "kill" grass seed. However, it will kill the sprout and the baby tap root as soon as the seed cracks. Therefore, the grass seed won't grow, and all seeds that come in contact with the soil, whether weed seeds or grass seed you planted, will die for about 4-6 months.
Will Pre Emergent Kill Bermuda Grass?
Will pre emergent kill grass? Answer: not established turfgrass. Note: I was at one of my wholesale fertilizer and herbicide suppliers last August. And I overheard an elderly, walk-in homeowner looking to fix all of the dead spots in his St. Augustine and, to quote, "prevent that darn bluegrass from being all over my yard this winter." The assistant manager of this location was working the desk and shockingly told him, "You really don't want to put down pre emergent as it might kill your St. Augustine." The homeowner said, "Really? I used to put out pre emergent all the time at my old house." So, the assistant manager changed course and said, "Well, you don't need to waste money on pre-emergent as a 'healthy stand of turfgrass is the best defense for weeds.' Let's put out some fertilizer and get your yard healthy." Separate from the fact that this assistant manager hurt his business by refusing to sell a product to a customer wanting to buy it, most of what he said was patently false and not backed by any science. Why?
- First, pre-emergent labeled for St. Augustine will not kill St. Augustine, or any other established lawn grass for that matter; hence, why it's called "pre-emergent" herbicide, not post emergent herbicide.
- Second, "a healthy stand of turfgrass is the best defense for weeds." This is a very famous saying in the turfgrass and horticulture industry, and it is true. And it goes right along with "a healthy immune system is the best defense for humans, to avoid getting sick." If you get a bacterial infection, do you opine about retroactively needing a healthier immune system, or do you start treatment for the infection and then worry about improving your overall health once the infection is gone?
- Part of keeping a healthy stand of turfgrass (whether Zoysia, Bermuda, St. Augustine, natural Buffalo, etc.) ensures the lawn is not full of weeds in the winter and spring. Once the warm-season grass comes out of dormancy and is ready to start growing again, it won't have to compete with aggressive, invading weeds.
Please check back for future tips on raising fine turfgrass in North and Central Texas. We serve all of north and central Texas for HOA landscape consultant services, and we offer diagnostic work, soil tests, lawn treatment, lawn spraying, and full-service lawn fertilization weed control services in Plano, Frisco, Mckinney, Dallas, The Colony, Lewisville, Allen, Richardson, Prosper and other areas in North DFW. DFW Turfgrass Science LLC.
