My lawn looks like crap. I see three problems--weeds, ant hills and bare spots. So I want to kill the weeds and the ants, and get grass to grow in the bare spots. I don't really need a perfect looking dark green lawn, but no weeds and good grass coverage would be nice.
Some of the bare areas are beneath a few large oak trees. I've heard that it's really tough to get grass to grow under trees, so I'm either taking the trees out or just put up a border and mulch around the trees.
It the area gets at least some light, about 3 hours a day or so, then you should be able to grow grass. Some trees, maples for example, can be impossible to grow grass under because they have lots of surface roots. But that should not be a problem with oaks. Be sure to use a grass seed blend for dense shade.
Another problem (I think)--two different kinds of grass in my yard. The prior owner planted zoysia on the side of the house, which gets a lot of sun. The rest of the lawn (sun and shade exposure) is (I'm guessing) some kind of rye/fescue blend. Do I need to treat the zoysia differently as far as fertilizing, weed killer, etc.?
Two diff grasses aren't a problem, but Zoysia in Philly sure is. In that area, Zoysia won't green up for another month. Then, come Oct, it goes to straw brown. Plus, it spreads aggressively. I'd wait till late Aug, then nuke it with Roundup and reseed. For your area, I'd go with a tall fescue/blue grass mix for the sunny areas.
In what order should I work on the lawn? Weed killer now, then ants, then wait 'till fall to put seed down? I'm in the Philadelphia, PA area.
I'd apply pre-emergent crab grass control plus fertilizer right now. For the weeds, unless they are everywhere, I'd use a 2 1/2 gallon tank sprayer with Weed B Gone or similar for spot treatment. I'd also get the soil tested, particularly the PH and lime if needed. You can put down insecticide for ants anytime, if they are a real problem. But fixing your other problems will encourage grass growth that will crowd out the weeds. I would not do any reseeding now, you are several weeks past optimal window for spring seeding. In the shady areas, spring is the best time to seed, as the trees have no leaves so it will get max light. But now tree leaves will be appearing, plus hotter temps, meaning more water, more comp from weeds, etc, so I'd wait to reseed the shady areas next spring.
In fall rent a core aerator for the whole lawn. For the sunny areas, after killing with Roundup and waiting 7 days+ for it to die off, you can reseed with a rented slice seeder