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 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.
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.
Once you pull up the label, hit “command F” on Mac or “control F” on PC and this opens up a search window. Type the word “Seed” in that window and it will reveal how many times that word appears in the label PDF.
You can spray it anytime you want leading up to seed day, and on seed day, but once your seeds germinate, you should NOT spray it again until the new gras has been mowed 2-4 times or 4 weeks whichever is longer.
Also of note, if you have crabgrass living after or during your seed grow in, you have to wait 28 days after emergence (when you see it) before spraying. It’s important to understand what mix you are seeding in this case because if you have a tall fescue, bluegrass mixed seed , the tall fescue will emerge in about 10 days but the bluegrass won’t emerge for 18-21 days so you need to wait 28 days AFTER THE BLUEGRASS emerges before spraying quinclorac. If you really want to be safe, wait the 28 days and 1-2 mowings before applying – this adds some extra protection for the late bloomers as mowing encourages new grass to “harden off” quicker.
( we have the generic which is cheaper FYI)I will throw this one in real quick because it’s a little different. We recommend this product for a pre-emergent application at the time of seeding. It will suppress certain weeds in your grow in. If you are new and inexperienced, DO NOT think you have to use this – your results will be ok without it. But if you do use it, people think they can just spray it anytime they want and this is not true.
So that is my first clue as to the reseed window – it comes from my experience.