For watering, I know you can grow grass in mid summer but you just gotta keep those new grasses watered well so heat doesn't fry them when they have short roots that can't find deeper water.

Even in Minnesota If nighttime temperatures stay above 70 degrees it is possible for pythium fungus to grow and kill your seedlings. Ryegrasses are particularly susceptible but it can kill all grasses. Don't ask me how I learned this, but I now avoid seeding in the summer. You can still do it, but you'll have to be careful and maybe use a fungicide.

 

I am not sure I understand, Roody. Did you start in the fall already?
I think you could go either way--if the weeds are bad--go for the weed control.
However, if weeds are not excessive I would use the "seed safe" crabgrass control at about week 4 to 6.
Follow up with a granular weed and feed product at about week 8 to 10.

Water whatever it takes to keep the soil moist relative to your temperature, soil sandiness and humidity. Avoid poor drainage or standing water on new seed, particularly if the night temperatures remain over 70--pythium fungus may attack under these conditions.

Once you have mowed twice you can cut back to water a half-inch twice per week. Put a coffee mug on the grass to estimate how much water you are applying per hour.
An organic fertilizer like Milorganite is fine in between these treatments.

 

thank you.

I know not to water at night or like 3-4 hours before sun goes down (the initial light ~7 min watering 2-3X a day, not a long soaking once the grass is established), but if it's still wet as you mentioned and remains over 70 degrees at night, pythium fungus may attack. Pretty easy to spot I would say based on a google image search, just gotta catch it early I guess and apply a Fungus Control but I'm hoping this isn't an issue.

In Fall, I did dethatch scalp and bag, then 6X aerate then slit seeded mine. And giving it another follow up seeding now instead of focusing on selectively killing weeds until Fall to do the seeding then. I might do a third final seeding in Fall though.
I got good results, some areas are ~%95 grass but some are weedy.

I plan to do ortho weed b gon but must "wait after new grass (being planting in about 3 days) is mowed 3 times" (or 4-5 weeks that translates to is what I found from googling). I can't use it for 4 weeks before the final seeding in Mid September, and can't use it more than twice a year.

I will take roggles suggestions. But shouldn't I apply seed-safe crabgrass control starter in a few days at the same times as seeding like I always have done? Instead wait 4-6 weeks ? Crabgrass might start already.

Scotts synthetic turf builder is 32-0-4
Scotts starter with crabgrass preventer 21-22-4
Scotts starter without crabgrass preventer 24-25-4
Milogranite 5-2-0

P Phosphorus (middle numbers) helps it sprout and root fast and K Potassium (3rd number) helps it withstand drought. But I guess these work in combination, in other words, it's not great for summer temperature if it has a lot of Potassium for drought control if there's not good roots from lack of phosphorus and vice versa.

Should I give it 21-22-4 now and then again in 4-5 weeks or will that be too much phosphorus?
Or is ample water more important than worrying about trying to use a starter fertilizer twice ?
Twice starter fert would total 42-44-8 in 5 weeks compared to the regular turf builder is 32-0-4. I realize I should get a soil test for phosphorus but it's too late for that. Maybe I should just do starter now and in about 5 (?) weeks do half starter half turf builder. The Turf builder 32-0-4 used to have phosphorus but it got so bad with the environment they omitted it from Turf builder in 2013. I plan to just use all these chems and water now to get it as thick of grass as I can and then see how it lasts thereafter with just organics, no/minimal phosphorus depending on soil test, and mowing high, and no/minimal water.

Scotts website says
http://www.scotts.com/smg/goART2/InfoHowTo/how-to-care-for-newly-planted-grass/19500088
"If you applied a Starter fertilizer when you planted your new grass, feed 4-6 weeks later with Scotts® Turf Builder® Lawn Fertilizer with 2% Iron to keep the new grass growing and maintain a thick, green appearance.

Continue with regular feedings every 6-8 weeks to provide the nutrients your lawn needs to crowd out weeds and withstand the stresses of heat, drought, and family activity."

so just do that ^ and make sure it gets plenty of water this first summer (as much or as little as it takes to keep the soil moist until sprouted to 4" and then do 1/2 - 3/4 inch of water all at once every 4 days until Fall?

 

Just a thought here, please forgive me if this is not helpful.

Personally I love science, scientifically prescribed procedures, treatments, and formulas, but at some point I need to let the subject of my scientific experiment tell me what it needs. Growing grass can seem fairly easy when I pay attention to what it needs and give it what it wants. Don’t be afraid to respond to “what your lawn is telling you”. Deviate from the “plan” sometimes if you need to, and see what works best for you and your lawn. Nature throws a curveball at me sometimes, and I make some mistakes but that’s what makes it fun for me.

 

Yes, I agree--use starter fertilizer with seed-safe crabgrass control if you are going to seed again this spring.
Yes, wait for new seed to be growing strong before the Weed B Gone. But the information is conservative--if you want to wait half as long--it will probably work--the risk is yours.
Once the seed has sprouted it does not need phosphorus..so use Turfbuilder without the phosphorus after sprouting. The roots will still grow just fine. 32-0-4 is fine.

New seed is best applied when the soil temperature in fall is high--this results in quick germination--August 15 around here. In any state, sow new seed when the day temperatures fall below 85. Or...8 weeks before frost.

And you are right--lack of ample water is the most frequent cause of seeding failure. Do not let it dry out.