Tulsa (and Oklahoma City for that matter) are both in a transitional zone, which means it’s really too hot for fescue, which is a cool season grass. We use fescue as a shade grass for this reason. In climates farther north, fescue will grow in full sun.
But here, in Tulsa and OKC, fescue’s growing season starts in September. All fescue lawns should be overseeded in the fall to keep them thick and healthy.
If you seed fescue now, it won’t have time to get a good root system down, before the heat of the summer. Fescue, like any other plant, needs light to grow and to make food for itself through the process of photosynthesis. In the fall, the leaves are falling off the trees, and it’s cooling off, and fescue thrives. It thrives most of the winter, and especially now in early spring, when the trees are not fully leafed out. Right now, fescue is going to look fabulous until the leaves are fully back on the trees and until it starts to get hot. When it gets hot, the fescue is again in the shade. Here’s the fescue cycle in Tulsa and OKC:
Fescue is seeded in the fall. Temperatures are cool, and the leaves are falling.
Fescue grass germinates and starts making food for itself, storing carbohydrates to last it through the hot summer.
Spring comes and fescue looks vibrant! It's still making food for itself, and it's still cool in the evenings.
Summer comes, and the trees are covered with leaves. Fescue is in the shade now, and it still looks good.
In mid-summer, temperatures soar to the 90's and over 100. Fescue is beginning to fade a little. It wilts in the high temperatures and must be watered daily, just to cool it off, although it still needs twice-weekly deep waterings. Take care to mow it high so there is sufficient leaf surface for it to make food for itself. Some of it dies due to the heat.
Fall comes, it's time to overseed, and the process starts over.
Another point: If you seed fescue now, you will have to forego the spring pre-emergent application for weeds. If you put down a pre-emergent, the fescue seed will not germinate.
Some people seed fescue spring and fall, just to be sure, or just because they have bare areas they can’t live with. Just bear in mind that if you have put down a pre-emergent, seeding is a waste of money. If you want to seed and then wait until it’s up and has been mowed twice, THEN you can put down a pre-emergent, if there is still time. (Basically, you need to get the pre-emergent down before the crabgrass germinates.)
Do you ever need to overseed Bermuda grass? No! Bermuda spreads by above-ground stolons and underground rhizomes. Proper mowing and fertilization will keep it thick, healthy, and spreading. If you have an established Bermuda lawn, you should never have to seed it.