It is time to fertilize the lawn. With the freezes this winter and the generally cool weather the lawn weeds have prospered but the lawn grass has been slow to begin growth. It is most efficient and environmentally appropriate to delay fertilization until the regular grass has grown enough to be mowed twice. That growth means that the roots are well enough developed and there is enough blade surface to provide transpiration to pick up the nitrogen.
Consider using a slow-release lawn fertilizer with a formula such as 19-5-9. The cost per unit of nitrogen is reasonable and the product provides both immediate and slowly released nitrogen. It is not necessary to fertilize again until fall.
Apply the fertilizer at a rate to provide one lb. of nitrogen per 1000 sq. ft. of lawn. Both the fertilizer bag and the fertilizer applicator will provide information on the setting to use to apply the recommended amount of fertilizer.
Mow the lawn as frequently as required to never have to remove more than one third of the grass blade. That usually means every week if you mow at the recommended heights of 3.5 inches for St Augustine grass, 2 inches tall for zoysia grass and 1.5 inches tall for Bermuda grass. Buffalo grass should be mowed infrequently at 5 inches tall. It does not make a dense sod and if it is mowed shorter than 5 inches will end up dominated by weeds.
If you are putting in a new lawn or changing a lawn grass because of shade, excess water use, or other concerns consider these issues for the various lawn grasses. By way of a general recommendation, if there is not 6 inches of soil on the planting site, add enough to make it 6 inches deep. It will be well worth the investment. Apply and rake or till in 10 cups of slow release lawn fertilizer (19-5-9 works well) to the soil before planting. Roll the sod once it is laid and water several times per week through the first growing season.
Bermuda grass has the most traffic tolerance and is the most drought tolerant. Bermuda grass requires full sun and can be established by seed. Zoysia grass is also capable of tolerating drought but requires as much water as St Augustine grass to stay green. It has good traffic tolerance and some shade tolerance. St Augustine is the easiest to mow and has the most shade tolerance but requires the most water to prosper. It is the most susceptible to diseases, traffic, and insects. Floratam is the St Augustine variety most resistant to problems. Buffalo grass requires full sun. It is very drought tolerant and can be grown from seed but is susceptible to weed invasion.