If you find that the weeds are recurring past the 6-8-week mark, you may wish to consider using a selective herbicide to spot spray your weeds. Some weed killers such as glyphosate (Roundup) kill more than just weeds, so it is important to not apply these as if they are not done precisely, they can kill your grass. Shop bought selective weed killers will recommend when to apply their product and how often and you should read the instructions thoroughly and adhere to them.
In short, here’s what you should do if you encounter weeds in your newly seeded lawn:
Although this can be frustrating and we can appreciate that a quick solution will be desired, the good news about these types of weeds is that they are largely shallow rooting and should come out with the first mow at the 6-8 week mark after sowing. If they don’t, they should be easy to pull out of the turf.
However, you can get rid of these weeds just as fast as they have appeared.
The important thing to remember when new weeds appear in your newly sown lawn is not to act hastily – do not apply a Feed, Weed and Moss Killer type product of any kind on a newly sown lawn.
If you find that when the lawn is at least six months old and has been taken over by weeds or moss, you can use a Feed, Weed and Moss Killer product.
Dandelion, clover, spurge, and numerous other broadleaf weeds are stimulated as well. If you should have just a few weeds here and there, pull them by hand. However, if you are overrun, fall is an excellent time to control those broadleaf weeds. Perennial broadleaf weeds are busy sucking up much-needed nutrients to store for overwintering. An application of Gordon’s Trimec or Speedzone can be applied 28 days after grass seed germination. A fall application of Gordon’s Trimec with Uncle’s Stikit, spreader sticker or a granular application of Loveland Weed and Feed will be quickly absorbed by the broadleaf weeds and is sure to kill to the roots.
Disturbing the soil (verticutting, aerating, dethatching or raking) exposes soil and any pre-existing weed seeds that lay dormant in the soil. These weed seeds could be from last year or several years ago, suspended under the soil, too deep to germinate waiting for their opportunity to spring into life.
When properly preparing your lawn for fall overseeding, you created a pathway for grass seed to reach the soil. If grass seed didn’t reach the soil, it would not grow. Raking, verticutting, dethatching, or core aerating are all methods to ensure seed to soil contact.
Controlling Broadleaf Weeds after Seeding
Each year during the fall over seeding season, we get a lot of folks that come in to the Grass Pad and say, “I followed your fall lawn renovation program; I used your weed-free grass seed. Why do I have weeds in my yard?” Our response is “Well, it means you really did it right!”
Grassy weed seeds appreciate the same fertilizer and additional watering from your fall renovation program and flourish. Don’t panic – annual grassy weeds will be slow to germinate as soil temperatures cool in fall. Mother Nature will take care of these annual weeds at first frost. Using Prevent, crabgrass preventer in mid-April will eliminate their return.