Grass seed grows fastest when a climate-appropriate variety is planted at the correct time of year. To promote fast growing, match the planting season to the type of grass, cover the seed with a thin layer of compost, and ensure the area remains moist.

Germination times for grass seed vary from three to 28 days, depending on the type of grass and the temperature and humidity. Grasses that prefer cool weather should be planted in the spring or fall for the fastest germination time. These varieties include Kentucky bluegrass, ryegrass and creeping bentgrass. Grasses that germinate faster in warmer temperatures should be planted during the summer, and include Bermuda grass, bahiagrass and zoysiagrass.

High-nitrogen fertilizers are not recommended for germinating grass. These fertilizers nourish weeds that compete with the grass. Lower nitrogen starter fertilizers and slow-release fertilizers encourage root growth and are safe to use on new grass. Higher nitrogen fertilizers can be introduced to mature grass after three months of growth.

Proper soil aeration and composition prior to planting the grass also encourages the fastest possible grass growth. Aerate compact soil with a rototiller, rake or shovel prior to planting grass seed. Powdered gypsum can also be added to the soil; this encourages drainage and improves the soil texture.