What is Cool Season Grass
Cool season grass thrives in the moderate spring and fall temperatures of the north and northern transition zone. Cool season grasses don't like the heat and can go dormant (turn brown) during extended hot, dry conditions. Supplemental water may be needed to keep the lawn green between rains. Cool season lawns usually contain a mixture of Bluegrass, Perennial Ryegrass and Fescues, allowing the lawn to adapt to your specific conditions.
A cool season lawn can best be established from seed or sod. When laying sod, it is important to keep it constantly moist until the sod roots into the soil. The best time to seed cool season grass is in the spring or fall, but it will germinate in the summer heat if kept moist.
Common Cool Season Grasses
Kentucky Bluegrass - A fine and tightly knit dark green grass, it is often mixed with other species for best results. It is popular throughout the northern and transition zones for its ability to grow in shady conditions. Bluegrass grows well in loose soil, so if you have heavy clay, aeration is necessary every few years. Mow at a height of 2-3" and your bluegrass should be able to withstand slight drought. A common problem is leafspot diseases, which is characterized by brown borders or tan centers to the leaf, and should be treated with fungicide. Make sure your seed bag label doesn't list Annual Bluegrass, it is a weed.
Perennial Ryegrass - Found primarily in the northern and transition zones, it does need full sun to thrive. Perennial Ryegrass has a medium texture and grows in clumps or bunches but is often blended with fescues and bluegrass for a uniform look and feel. Because of its fast growth it is often used to overseed a dormant lawn in the south, giving the homeowner a green lawn year round. Set your mower height to 2-3" and don't be tempted to save money by getting Annual ryegrass, it is much rougher and much less attractive.
Fine Fescue - An excellent performer in shade and cold, this is often added to fill in where other cool season species fail. It has three varieties; creeping red fescue, hard fescue and chewings fescue. A heatwave of more than a week, could require more care and watering, as high temps stress this grass out. Fine fescue a good choice for high traffic areas and can handle most soil conditions and climates. Plant it in the spring so it grows in early and fast, then mow at a height of 2-3".
Tall Fescue - Usually used in mixes due to it's adaptability, quick germination, and low maintenance. A coarse textured, dense grass that grows in clumps and loves the shade. Tall fescue is extremely wear tolerant and is popular on sports fields and other high traffic lawns.
Read about drought tolerant cool season grasses here