Over-seeding is a good annual practice where you scatter grass seed over your entire lawn if its thin, and/or over any bare areas. Grass seed wont sprout until the soil temperature reaches 50 degrees so theres no point in putting grass seed down too early. A good rule of thumb is to over-seed when the forsythia (bushy shrubs with bright yellow flowers in late April-early May) are just finishing blooming.
Keep in mind that the seed needs to make contact with the soil in order to sprout. Most seed that is just broadcast over existing lawns sticks to the grass blades and doesnt make it to the soil. To help the seed reach the soil wait until the grass is dry before over-seeding then drag a rake lightly over the grass to jostle the seed off the leaf blades.
Dead patches should be raked hard with a stiff iron rake to loosen the soil. Then mix some topsoil with some grass seed in a bucket and spread an inch of this mixture over the bare area. Tamp it down with your foot if its a small patch or rent a roller for a larger area. Pressing the seed into the soil makes a huge difference in how quickly the seed will sprout. Youre in a race this time of year against all the weed seeds that are sprouting, so you want to give your new grass plants as much of an advantage as possible.
Frank Rossi, turf specialist at Cornell University, says it is always helpful to use starter fertilizer whenever you are re-seeding bare areas. Dont use it if youre just over-seeding an existing lawn but do use it in any areas where youre starting over.
Crabgrass is a real problem in lawns that suffered during past years hot summers. Its an annual grassy weed that thrives in the hot weather that is so hard on our cool-season lawn grasses. If you dont have a problem with crabgrass you can prevent it by feeding your lawn each fall to keep it dense and thick. In this way any crabgrass seeds that blow into your lawn in early summer have no place to sprout.