If you stick to the products you can buy from the big box stores, that’s
probably the best plan (i.e. wait till the next fall).
However, lawn care is also about your expectation, your current situation,
and how much time and money you want to spend.
To make it some fun for you, I throw in 2 products which you can research
online. They are also available from online stores if you decide to use
them. You will find that suddenly you have so many more options (basically
you should see a new horizon).
Active ingredient: quinclorac (e.g. Drive XLR8). This one has very good
post-emergent control for crabgrass and some other weeds but not poa annua.
It can be applied 6 weeks after seeding.
Active ingredient: mesotrione (e.g. Tenacity). This one is a pre-emergent
for both crabgrass and poa annua (and many other weeds). However, its pre-
emergent effect lasts only about 4-6 weeks. It is also a very good post-
emergent for both crabgrass and poa annua (and many other weeds). It can be
applied during seeding time (remarkable!) However, it has an annual
application limit of 16oz/acre, so you shouldn’t expect to apply it too
many times per year.
The traditional pre-emergents (e.g. crabgrass preventer) normally need a
waiting period of about 8 weeks after seeding before application, although
they last about 3 to 8 months.
(I can see your brain is already churning :-)
For traditional pre-emergents, I recommend products with active ingredient
prodiamine (e.g. Barricade) or dithiopyr (e.g. Dimension). If you can’t
find those, using pendimethalin (e.g. Halts) from the big box stores should
be fine.
Remember to add surfactant to post-emergents and spray to the leaves
directly and don’t water afterwards. For post-emergent, always water in
after application, even for liquid sprays.
I still think fall overseeding/renovation is much better than a spring one
for cool season grass. Apart from the weed pressure differences (spring
time normally germinates much more weeds), another factor is that summer
heat might just kill new seedlings before they are mature enough if it is
too hot and/or you plant too late and/or watering isn’t maintained
adequately in the heat of the summer. It is one risk you need to consider
for a spring seeding.
Note the above discussion is mostly applicable to cool season grass. For
warm season grass, it may be another story.
I strongly suggest you do a proper soil test (e.g. Logan Labs or UMASS soil
lab) if you haven’t done so already, and amend your soil accordingly before
your next seeding.
And don’t forget proper watering (deep and infrequent) and mowing (never
cut more than 1/3rd of the current height) practices.
