Iis it too late (9-16-24) to both Kill weeds and plant grass seeds this fall - Ask Extension
Today is 9-16-24. I have yet to apply weed killer, or put down grass seeds for the Fall. Is it to late to do both. How late can I plant seeds this Fal...
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Iis it too late (9-16-24) to both Kill weeds and plant grass seeds this fall #885393
Asked September 16, 2024, 10:53 AM EDT
Today is 9-16-24. I have yet to apply weed killer, or put down grass seeds for the Fall. Is it to late to do both. How late can I plant seeds this Fall?
If I have to choose one, should I kill the weeds, or plant new grass?
Thank you,
Andre
Prince George's County Maryland
Expert Response
It's not too late to put down grass seed for cool-season grasses like tall fescue, since that window of time runs through about mid-October (the sooner the better, though), but if you have to prioritize one over the other, we'd recommend seeding and waiting for weed control until spring. That said, what weeds are you targeting with pre-emergent? Only winter annual weeds can be suppressed this time of year using pre-emergent (though it might be getting late for some of them, as germination has already begun in some cases); summer annual weeds are treated in spring.
Depending on the pre-emergent (whether it affects grasses or only broadleaf plants), you also might not have time to apply it while still being able to sow grass seed, so for that reason as well, waiting until next year might be prudent. Pre-emergent only prevents germination, so if that window is missed, you still might be able to use a post-emergent on already-growing weeds later, depending on the weed species, chemical chosen, and how that chemical might impact young turfgrass.
Miri
Depending on the pre-emergent (whether it affects grasses or only broadleaf plants), you also might not have time to apply it while still being able to sow grass seed, so for that reason as well, waiting until next year might be prudent. Pre-emergent only prevents germination, so if that window is missed, you still might be able to use a post-emergent on already-growing weeds later, depending on the weed species, chemical chosen, and how that chemical might impact young turfgrass.
Miri
Miri, thank you so much for your guidance.
Based on your response, I think I will go ahead and put down the grass seeds and wait until the spring to kill the weeds. Could you recommend some pre emergents (I have not had much success in killing weeds in my lawn).
Also, in the past I have always put down fertilizer at the same I put down the grass seed.
Is that a good idea?
Could you recommend some fertilizers to apply wirh the grass seeds?
Thanks again, very much,
Andre
You're welcome.
We can guide you as to pre-emergent options once we know what the particular weeds are that are growing in the lawn. If you aren't sure about their ID, feel free to send us photos of foliage. (Flowers are also very helpful with plant ID, though not many weeds are blooming now; foliage is sometimes distinctive enough, though.) While we don't recommend particular brands or companies, we can let you know what active ingredient(s) to look for in a herbicide.
Yes, you can fertilize when you overseed. Ideally, fertilization is done based on the results of a laboratory soil test (performed every 3 years or so...it doesn't have to be yearly). That way, you know if there are any nutrients that are low and need particular supplementation. It also lets you know if you're allowed to apply phosphorus [P], a common fertilizer ingredient (in the N-P-K analysis), since lawns not testing low in P cannot legally apply it with lawn fertilization to comply with Maryland lawn fertilizer law. Soil testing also lets you know if applying lime would boost grass growth (doing it without test results could be over-applying nutrients like calcium while being an unnecessary step if the soil acidity is already in the range preferred by turfgrass). Soil acidity (pH) level influences how easily plant roots can access nutrients, so a soil could have plentiful nutrients but not have them very accessible to the grass roots if the soil pH is too far out of range. (This is not very likely, but it's not something that can be determined without a soil test.)
For fertilization, our Lawn Fertilizer Schedule and Fertilizing Home Lawns pages provide guidance. Since much of the state is still under drought status, be sure to monitor the lawn for watering needs so any fertilizer applied can be absorbed. Grass seed is also intolerant of drying out for too long during the germination process, so be especially mindful of watering needs during its first few weeks so it establishes well and can make the most use of the added nutrients.
Miri
We can guide you as to pre-emergent options once we know what the particular weeds are that are growing in the lawn. If you aren't sure about their ID, feel free to send us photos of foliage. (Flowers are also very helpful with plant ID, though not many weeds are blooming now; foliage is sometimes distinctive enough, though.) While we don't recommend particular brands or companies, we can let you know what active ingredient(s) to look for in a herbicide.
Yes, you can fertilize when you overseed. Ideally, fertilization is done based on the results of a laboratory soil test (performed every 3 years or so...it doesn't have to be yearly). That way, you know if there are any nutrients that are low and need particular supplementation. It also lets you know if you're allowed to apply phosphorus [P], a common fertilizer ingredient (in the N-P-K analysis), since lawns not testing low in P cannot legally apply it with lawn fertilization to comply with Maryland lawn fertilizer law. Soil testing also lets you know if applying lime would boost grass growth (doing it without test results could be over-applying nutrients like calcium while being an unnecessary step if the soil acidity is already in the range preferred by turfgrass). Soil acidity (pH) level influences how easily plant roots can access nutrients, so a soil could have plentiful nutrients but not have them very accessible to the grass roots if the soil pH is too far out of range. (This is not very likely, but it's not something that can be determined without a soil test.)
For fertilization, our Lawn Fertilizer Schedule and Fertilizing Home Lawns pages provide guidance. Since much of the state is still under drought status, be sure to monitor the lawn for watering needs so any fertilizer applied can be absorbed. Grass seed is also intolerant of drying out for too long during the germination process, so be especially mindful of watering needs during its first few weeks so it establishes well and can make the most use of the added nutrients.
Miri
