As I have been explained to, dont quote me, but when you are growing grass the roots must develop a CROWN in the soil.
This CROWN once developed will cover the roots and allows the grass to go dormant, thus being able to grow back.
When you start new seed, the thing to remember is that it must constantly be moist. When the seed is moist, and then dries up, it will not come back.
Fall is the best time to seed, but make sure it is not too late in the fall. Once the seed freezes, its basically all over.
Using an overseeder is great because it actually cuts lines in your lawn and brushes the seed into the cut lines so the seed makes direct contact with the soil so you have a perfect combination, seed and soil. The only thing missing now is the moisture, and that is why spring and fall are best.
If you have an irrigation system however, and are using it properly, you may be able to over come this seasonal
problem.
Test an area first to see if it will work for you, and make sure to use a Starter Fertilizer.
Once your grass is growing, get on a professional fertilizing program for your area. You should be able to find in your local area someone to TEST the soil. In our area, for $25, you can send a soil sample to JOHN DEMPSEY and they will return you with he results of what you should do to optimize your lawn.
You will get a report back giving you numbers such as 10-10 30, etc. Bring this number to a real fertilization store, something like LESCO and they will hook you up.
Good luck
IMHO
Danny