Geography, Climate & Grass Choice

Just as you select the flowers, vegetables, trees and shrubs for your yard and garden based largely on your climate, you need to choose turfgrass that thrives in your yard. Like any other plant, turfgrass has its own needs and characteristics, including relative tolerance to sun and shade, heat preferences, and water requirements. The type of seed or sod you select for lawn planting or renovation should not be chosen based simply on whether you live in a cool or warm part of the country, but should take into account regional variations. Fortunately, there is a very good resource to help you do just that.

The map below is a representation of the Turfgrass Climate Zone Map developed by the United States National Arboretum. Similar to the American Horticultural Society Heat Zone Map that gardeners often use, this map divides the country into five separate zones. The characteristics of each zone determine which turfgrass or grasses will do best in that zone. You may find other turfgrass zone maps; seed companies sometimes develop their own to reflect the species and varieties they have developed. But this version is the most common and, for most purposes, it’s a very effective resource in choosing the specific grass that will work best in your location.

The map breaks the country into the following five zones:

Cool arid (1). Encompassing such a large geographic region, it should be no surprise that this zone features an incredible diversity of microclimates. Mild, snowy-to-dry winters are the flip side of warm-to-very hot, dry summers. The diversity of this zone makes it a good idea to contact your local cooperative extension office or university agricultural program for help in choosing just the right grass. Kentucky bluegrass is one of the most common to this region and will do well, but given the relatively modest rainfall throughout the zone, you should plan on regular watering for best growth.

Cool humid (2). Another diverse zone, this is a region of extremes. Within the boundaries of this zone, there are frigid-to-mild winters, and hot to temperate summers. But moisture comes with all seasons. Most of the cool-season grasses do well in this zone.

Warm humid (3). A typical southern region, this zone features uniformly mild, wet winters, and hot, humid summers. The abundance of moisture provides a breeding ground for insects and a hospitable environment for many different lawn diseases, so vigilance is key in this zone. Treat any problems with the appropriate solution as soon as signs of disease become apparent. Bermuda grass, St. Augustine grass, and zoysia grass all do well in this region.

Warm arid (4). This is perhaps the most difficult region in which to maintain a lush, dense, and deep green lawn. The big challenge is, of course, water; options such as in-ground sprinklers, drip hoses and grey water systems are all part of lawn care here. The most common species throughout this zone is Bermuda grass.

Transition zone (5). Running along the center of the country from the east coast to around Missouri, this zone represents the most challenging area for growing turfgrass. Harsh summers and freezing winters mean that neither cool-season nor warm-season grasses are going to do well everywhere in the zone. The answer is to use Interstate 80 as a dividing line. If you’re north of that line, cool-season grasses such as perennial ryegrass will probably work best in your yard. If you’re south of the line, and experience milder winters, consider growing Bermuda grass.

Understanding Microclimates

The Turfgrass Climate Zone Map is an excellent tool, but it can’t account for all geographic elevations and variations. Certain “microclimates” sometimes feature completely different conditions than the zone within which they are located. If your home is located within a microclimate, you need to take that into account when choosing seed or sod.

A microclimate is created when a local feature causes a small area to experience much different conditions than the surrounding geography. For instance, if you live in the cool/arid zone, but your home is located in a deep valley where fog is common in the summer, it’s likely that you could consider a less drought-tolerant species than could survive elsewhere in your region. Likewise, if your yard is shaded most of the day and is at the foot of a watershed slope, you’ll have much wetter conditions than your neighbors.

Being aware of your local and site conditions helps you further refine your choice of turfgrass, and can play a large part in just how well your particular grass grows.

Local conditions such as frequent snowfall and freezing temperatures will affect what grass type you should overseed with or plant in the first place.