When to Apply Pre Emergent, is the most searched question about pre-emergent herbicide on Google. Then it is followed by What Month do you put Down Pre Emergent? And 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 application of pre emergent on Texas lawns, including amongst so called lawn treatment professionals (which the super majority have no educational background and just call themselves experts), is that 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 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 on really cold winters). This pre emergent, weed control application is primarily made to stop crabgrass, goosegrass, dallasgrass and most other broadleaf weeds in the early summer months.  Important note: this is not a situation of "the early bird gets the worm." I see some homeowners putting it down on nice north Texas days around New Years, and I see some unscrupulous (because they are not busy) lawn spray and lawn treatment companies putting it from Christmas to mid-January. If you put down pre-emergent in north Texas before the end of January you might end up with crabgrass in July or August, along with throwing away a portion of your chemical cost.

The second time to apply pre-emergent in north Texas is from August 7- September 7 (unless you overseed with winter ryegrass). In our opinion this application is more important than the known winter application. Why? Because your lawn is brown. And nothing looks worse than having a dormant, brown lawn full of green weeds. This summer application of pre emergent will stop ugly winter weeds like poa annua (annual bluegrass), dandelions, chickweed, clover, dollar weed, etc. 

How Long After Pre Emergent can I Fertilize?

Some detail oriented homeowners want to know how long after pre emergent can I fertilize? Answer: immediately. Several retail pre emergents are actually blended in with fertilizer (which we don't choose to use, but nothing is wrong with it). 

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:

1. Most pre emergents have three different application levels - minimum, average, maximum. The thickness of the invisible soil barrier is directly applicable to how heavy you applied it.
2. Did you lightly water it in to get it set into the top soil layer? Or did you get a really heavy rain, or overwater, which diluted/washed it from various areas in your lawn?
3. After you applied the pre emergent did you do any type of lawn aeration, topdressing (with sand or organic matter), or deep dethatching? If you did you ruined the majority of the pre emergent "barrier."
4. Are you using the same pre emergent every year? It is important to mix up the brand of pre-emergent you use every couple of years. Weeds can become immune to "medicine" just like viruses and bacteria can in humans. That does not mean you need to stop using your favorite pre-emergent forever, just rotate in a new pre-emergent herbicide every few years.

How long is pre emergent effective, is directly attributable to all of the factors above. 

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 smart 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, are going to die for about 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 somehow 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 the following "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 then 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, these were irresponsible things to say. 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."  That said, if you get a bacterial infection do you opine about you 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.), is making sure the lawn is not full of weeds in the winter and spring; and 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 soil testing near me, 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.