When can I put weed killer down after overseeding?
Applying pre-emergents or herbicides too soon after overseeding risks damaging your newly germinated grass, but waiting too long risks losing control of weeds like poa annua, wild violets, clover, and dandelions before winter. This leaves lawn owners struggling to figure out the exact safe timing and product choices for weed control during the fall transition.
What people tried
Every workaround mentioned in the threads below. We haven’t tested any of them — and nobody here is claiming they worked.
- 1Waiting 45 to 60 days post germination and/or 2-3 mowings before applying any pre-emergents or herbicides.
- 2Choosing between seeding or applying a fall pre-emergent since doing both simultaneously is restricted.
- 3Aerating and overseeding in September while waiting to apply pre-emergent in the spring.
- 4Waiting for the lime to set in slowly over time
- 5Using fast-acting commercial pH adjustment products
In their words
Unedited, most upvoted first, each linked to the thread it came from.
“I over seeded my TTTF lawn two weeks ago. I’m looking for advice on timing and type of pre-emergent for mainly poa annua, wild violets, clover and dandelions.”source ↗
“What’s the best way to fix this? In Colorado for reference. Not sure if I have time before winter?”source ↗
“Hi there - planning to put down pre-emergent next spring. I have a TON of crabgrass. My question is, can I aerate and overseed now in September and do the pre-emergent in spring with no issues? The seed will be far enough along the pre-emergent won’t affect it?”source ↗
“I was thinking about adding agricultural lime as well, since the solid is basically pure clay. Anything to think about in relation to timing with the seed? Would it be harmful to do it now?”source ↗
Where this came up
People with this problem also raised
- 3When is it safe to mow newly seeded grass?
- 18Can you plant grass seed late in the season after missing the window?
- 4Will heavy rain wash away grass seed after overseeding?
- 10How to water new grass seed with a full-time job
- 2When is the right time to apply fall fertilizer?
- 86Why is my overseeding failing to grow?