How long do you need to wait after what? After spraying? You don't need
Also, with a little TLC, your existing grass will probably fill in without
reseeding. I was shocked last year to discover how much damage the violets
and creeping charlie had done to a patch of my lawn. I started watering it
more and pulling the weeds, and there was very little grass left. But the
grass filled in nicely before I got around to reseeding. When I got rid of
the creeping charlie and most if the violets, the grass was able to crowd
out most of the other weeds (for some reason there were no dandelions here;
I woulda spot treated them with 2,4-d if there were.) I think the creeping
charlie choked out the dandelions :-/
If you are using a broadleaf killer, there's no necessary gap
between spraying and seeding. However, there are some other
practicalities involved. IME this process works better if you:
1. Make sure the lawn is well-watered and not mowed for about a
week; this assures that the weeds are actively growing.
2. Apply herbicide.
3. Mow lawn a week later; resume watering and not-mowing for 2-3
weeks; this gives all the broadleaf seeds an opportunity to
germinate and establish.
4. Apply herbicide.
5. Mow lawn a week later; reseed.
You want reseeding to take place after temperatures have begun to
ameliorate in the fall, but enough before when the ground freezes
that the grass has an opportunity to create vigorous roots and
crowns . . . that's about a month. So, what you need to do is
find out the average date of ground freezing in your area, and
work back by 9-10 weeks to figure the last date on which you
could reasonably start this project. The first date will
typically be 2-4 weeks prior to that. So, if your ground-frost
average date is 15 December; you'd want to start this project
between 8 September and 6 October.
An alternative, and somewhat safer option in northern climes is
to kill of the weeds this late summer and fall, and reseed in
At least 60 days, 90 days is better. Spring is a much better time to
treat broadleaf weeds. I would hand pull weeds 90 days prior to
overseeding. If you have very little grass, you can use RoundUp over
the entire lawn, then reseed in two weeks. If you use the RoundUp
method it would be a good time to spread a load of topsoil and compost
just before seeding.
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