Homeowners who lay sod rather than seed grass are said to get an "instant lawn" according to the website of Washington State University. Seed germination only occurs in narrow time frames, limiting when you can seed lawns. Sod is already growing grass and has fewer limits as to weather conditions.
Sod vs. Seed
Lawn seeding is usually more cost effective than laying sod. However, the sod gives the property owner that instant lawn and instant gratification. Lawn seeding is best done in the early spring or fall. If the need for a finished lawn falls outside those time windows sod may be the only option. It commonly becomes a decision based on the quick sod project versus the slower and cheaper route of seeding grass. Each homeowner makes the decision based on his own beliefs, economics and time constraints.
Homeowners can place sod successfully almost any time during the year, according to Washington State University. Ideally, place the sod just before the time natural moisture will be most plentiful to reduce the amount of irrigation required during the first six months of the lawn.
Sod West of the Cascades
Lawn seeding or sod applications west of the Cascades are best done in the early fall, according to Seattle Public Utilities. This generally means in September or the first half of October and that the sod's early months are during the cool months of the year. This minimizes but does not eliminate the need for lawn watering during the first six months the sod is place. Monitor the lawn and water anytime the top two inches are dry to the touch.
Another reason for laying sod in the early fall is it gives you the summer to prepare. Work the top soil with a tiller to about 6 inches. Water the ground and allow weeds to sprout before tilling the ground again to kill off the weeds and prepare the soil bed. Rake the soil level and pack it firm in preparation for the sod.