Many of us have found an old bag or box of grass seed in the back of the shelf of cabinet in the garage and wondered if it would grow. The answer, of course, is "Maybe." Depending on how it has been kept and how it is planted, grass seed can remain viable for years. Seed grows to maturity with a set of biological preconditions that "program" it to germinate only under conditions that allow the plant to survive. As each year passes, only the strongest seeds survive.
Test seeds for viability by counting out 100 seeds and scattering them in potting soil in an empty milk carton or other container. Put your "test batch" in a sunny window and keep it moist, not wet, for several weeks until the grass is up. Count the number of blades to determine the percentage of germination you can expect.
Top-dress your lawn bed with compost mixed with an equal part of humus or manure. Work the top dressing in well to create an optimally fertile bed.
Remove all rocks and weeds. Break up clumps of dirt so that the soil is fine enough to rake flat. Level the lawn bed as you go so that water does not stand in puddles.
Scatter seed in early fall according to the corrected germination rate. For example; if the original germination rate was 97 percent and the actual germination rate is 50 percent, spread the seed at twice the rate as normal. Water gently but well so that the seed settles into the soil.
Keep the seed moist until germination. Water young grass in the early morning to minimize the chance of evaporation or fungus due to water sitting overnight. Wait to mow until the grass reaches 3-4 inches tall and remove only a third of the leaf.