The grass appears to be Kentucky Bluegrass(KBG). KBG will spread on its own via rhizomes if provided with the conditions it needs to thrive. From the pictures, it does not appear that it is necessary or desirable for you to seed. Overseeding KBG is often a futile endeavor, as it takes long to germinate (up to 3 weeks) and it has a hard time competing with the already established grass. Also, Poa A germinates about the same time as KBG (they are in the same family after all), and so it will be tough to control the Poa A since it will germinate right along with the bluegrass.

Plan of action:

- Do nothing but weed control via spot-spraying until mid-August.

- Fertilize mid-August using a nitrogen rich fertilizer at a rate of 1 lb N/thousand sq ft.

- Apply pre-emergent early September to stop the Poa Annua. You may need to re-apply late fall, read the bag instructions.

- Apply 1 lb N/thousand sq ft mid-September and mid-October.

- Apply 2 lbs urea/thousand sq ft mid-November as winterizer.

- Mow the bluegrass as high as your mower will go until summer is done.

- Drop your height of cut to 2.5"-3" in the fall to encourage spreading.

- At the beginning of fall, pull plugs of grass from healthy areas and transplant them into the bare spots. They will spread and fill in.

This should get your lawn in good shape by next spring.

I hope dchall comes along with the watering mantra, you will need that as well.

Uh, I just noticed you used the S word. What are we talking as far as direct sun, how many hours a day? KBG likes full sun.

Thanks very much for the quick and thorough response - great information.

Different parts of front and back get different sunlight, but average is maybe 5-6 hours of direct sunlight.

I wasn't aware of the plugging technique. Having googled it now, would you recommend plugging from sod, or only directly from my lawn. There aren't that many healthy areas on my yard I can pull from.

Thanks

I wouldn't recommend plugging from sod, because it may not match what you already have. You may end up with a splotchy lawn if the cultivars have significantly different genetic color. Also, some cultivars grow faster/slower than others, so it could just lead to all sorts of unevenness.

If you don't have a lot of good areas to plug from, give it some time in the fall and as the grass gets healthier and healthier it will spread and give you more area to plug from. In the pictures you posted, the grass actually looks pretty good, treat it well and it will fill in.

5-6 hours of direct sun should be fine. Areas that get much less than that will probably struggle.

Pics could just be KBG seeding. If I were you, j4c11's plan sounds good. I would not seed in the fall. You'd be surprised how well a cool-season lawn takes to liberal fall fertilization.