The best time to plant grass seed in Oklahoma depends on the grass type. For warm-season grasses like Bermuda, the optimal time to seed is late spring to early summer (May through June) when soil temperatures consistently reach 65-70°F. For cool-season grasses like Fescue, the absolute best time to seed is early fall (September to mid-October).
Why timing matters
If you plant Fescue seed in the spring, the young, fragile roots will not be established enough to survive the 100-degree Oklahoma summer heat, and the grass will likely die. Conversely, if you plant Bermuda seed in the fall, the first frost will kill the seedlings before they can establish.
Sod vs. Seed
While seeding is cheaper, laying sod is highly recommended for Bermuda grass in Oklahoma. Sod provides an instant, weed-free lawn and can be installed almost year-round, provided the ground isn't frozen.