By mid-February, the most common subject in our showroom is “Do you think we’ll get an early spring?” My standby answer is always March 20, but instead of relying on the calendar there are some clear ways to anticipate when lawns germinate.
The U.S. Department of Agriculture publishes a plant hardiness zone map. The 2012 map separates the United States into 13 zones with multiple subzones. If you love to learn about your zone, their website is pretty interesting (visit it here). The map does show a clear line between regions with cool-season grasses and warm-season grasses. In the eastern US, Interstate 70 closely follows the line between these regions. Most homeowners have lawns with both cool and warm season grasses and understanding the blends in your lawn helps predict when and how to mow.
The ability to go dormant under duress defines a quality grass species. Common cool season grasses go dormant when temperatures fall below 40 degrees and during dry conditions above 90 degrees. Warm-season grasses typically tolerate higher temperatures. They also tend to be more adaptive than cool-season grasses. Warm season grasses halt growth during cold dips and respond quickly when temperatures rise. As the map I referenced above demonstrates, history displays a pattern for typical growth periods.
Nearly every spring, cool season grasses will germinate in very late March and flourish throughout April and May. Regions north of I-70 typically feature cool-season grasses like Kentucky Blue grass, perennial rye grass and blue fescue. Ground and air temperature trigger the growth of these plants. When the ground temperature reaches 55 to 65 degrees, the roots begin absorbing moisture and ground nutrients. When air temperature maintains 60 to 75 degrees, the grass plant begins to grow. As all of us who live in the cool-season region can attest, once growth begins these lawns are incredibly healthy.
Species like Bermuda grass and St. Augustine grass require much higher temperatures before emerging. Soil temperatures above 70 degrees are needed for most warm season species. When daytime temperatures reach 80 degrees and nighttime temperatures don’t dip below 65 degrees, warm-season grasses will thrive. In southern regions of the United States, these grasses will remain hardy from the first of March through September. Warm-season grasses are a bit more agile than cool-season counterparts. Because these species may stunt growth in response to dips and spikes in temperature, I like to add blend warm season species into sunny spots, high traffic areas and along hills even in cooler regions. When temperatures stabilize, warm-season grass will quickly recover and prevent bare patches.
Spring seed tips
Whether recovering or planting new seed in your lawn, consider when and what to plant. Many weeds grow like warm-season grasses. So cool-season grass seed is ideally planted in the fall and early spring when temperatures are still mild. The new grass seed will germinate before weeds have a chance to grow. Warm-season grass seed won’t grow until temperatures rise. If these species are planted too early in the season, the seeds may wash away or simply be pushed out by weeds. Also consider planting the right grass for the needs of your lawn. As I mentioned earlier, I like to blend my lawn with a mix of cool and warm season species.