overseeding
Perennial Ryegrass: Where It Fits in a Northeast Lawn
Perennial ryegrass sprouts in a week and takes heavy wear, but it's the least winter-hardy lawn grass. How much to use, when to seed, what to mix it with.
Dormant Seeding: When & How to Seed Your Lawn in Winter
Dormant seeding lets seed sit through winter and sprout early in spring. When to do it, how much seed to use, and the spring mistake to avoid.