The U.S. Department of Agriculture has divided North America into regional hardiness zones based on average annual minimum temperature ranges. The minimum temperatures in zones 4 to 6 range from minus 30 degrees Fahrenheit, the lowest temperature in Zone 4, to the high of zero F in Zone 6. Turf grass in these zones must grow deep enough to withstand the cold temperatures of winter and the warm temperatures of summer.
Bent Grass and Bluegrass
Bent grass grows low and is the most tolerant of close mowing, according to the American Horticultural Society's “Encyclopedia of Gardening.” Bent grass is usually used with other cool-season grasses for lawns that experience moderate wear and tear, such as putting greens. Bent grass requires full sun and is prone to damage in the winter because of its weak growth cycle. Bent grass requires the most care of all the zones 4 to 6 grasses.
Kentucky bluegrass is also suited for zones 4 to 6, according to the American Horticultural Society, because of it resistance to wear. Kentucky bluegrass thrives in fertile soil and is used to create high-quality and durable lawns because of its uniform color and texture. The society recommends watering during dry spells and lightly fertilizing in late summer and early fall.
Fescues—fineleaf, red and tall—also are used in zones 4 to 6, according to Jerry Baker in his book, “Green Grass Magic.” Fineleaf fescues are suited for moderate-traffic lawns with little to no sun, and require very little mowing. The fineleaf fescue thrives in sandy, acidic and infertile soils and tends to overtake other grasses.
Red fescue is suited for lawns with low to moderate traffic and should be mixed with ryegrass to prevent the grass from growing clumps, Baker said. Red fescue should also not be over fertilized and especially not overwatered, as too much water can invite fungus.
Tall fescue is most suited for heavy traffic areas such as playgrounds, according to Baker, because of its coarse blades and deep roots, and should be mixed with other grasses. Tall fescue needs regular watering in the summer to prevent dormancy and is adaptable to most soils.
Perennial ryegrasses are most often mixed with other grasses in moderate-use lawns, according to “The Complete Guide to Gardening and Landscaping” from Time-Life Books. Ryegrass is best grown in full sun to light shade, and germinates quickly. However, it requires frequent fertilization and is prone to disease in the summer, specifically pythium blight, a fungus that turns the lawn brown.