patches

new seed

tiny weeds that will soon take over that area

I'm thinking about first de thatching (with a rental machine) the lawn, then treating weeds and overseeding after that. Does that sound like a plan of action? And what would the best weed killer be?

To be blunt, no it doesn't. Kentucky bluegrass is supposed to be dense (thick). I'm going with the idea that your grass is normal; however, your answers to a few questions might sway my opinion. If you watered the lawn daily or every other day, and you fertilized with liquid fertilizer (TruGreen or any lawn spray company), then it is possible you have thatch. If you have been watering deeply (a full inch all at one time) and infrequently (no more than once per week when temps climb into the 90s), then there is no chance you have thatch.

Your Kentucky bluegrass is not completely out of dormancy yet. In fact it might not have started to come out of dormancy depending on if you have other grasses, like fescue, in the mix. Those brown patches are dormant KBG. The green patches are either fescue or KBG which has awakened. I could be wrong but I believe the tiny weeds you refer to in the picture is this year's Kentucky bluegrass awakening.

Seeding in the spring is usually a problem for two reasons. 1) spring seeded grass cannot usually handle the summer heat...unless you live in a zone lower than 6. It would help to know where you live, but you might have a half a chance of making it through the summer with your new grass seed. 2) spring is when the crabgrass seed is sprouting. Crabgrass is a summer annual plant which is custom designed to thrive in the summer heat and fill every speck of open soil. Crabgrass this summer is not the end of the world, but you likely won't win Yard of the Month this year. Late summer is the time to evaluate your lawn and early fall (August for you) is the time to take action. Fall seeded lawns have all fall, winter, and spring to develop a root system to fight through the summer heat. By spring the turf should be too dense for crabgrass to get a start.

I don't keep up with weed killers, so look for someone else to come along. In general they work better after the weeds have been fertilized. The time to fertilize in the spring is after you mow real grass (not weeds) for the second time. Waiting ensures that your roots are working. Then fertilize and 2 weeks after that you can spot spray with the appropriate weed killer.

The tiny weeds are not KBG, unfortunately. That's what I thought last spring, when it was just coming up. I can get a better picture when it matures a bit more.

I do have another question. Plan for now is to get a handle on the weeds then overseed nearer to fall. My entire lawn seems to be a hodgepodge of grasses. However, there is one small area that has perfect grass (for me), it's soft on the bare feet, is thick and stays green even when the other grass is fading. I was hoping someone might know what it is, so I can overseed with the same type for the rest of the lawn.

Here is a second pic from further away.