It’s no fun being in the middle sometimes. Think middle child. Think airplane middle seat.
So it is with homeowners in the horizontal band across the middle of the United States, who have both boiling summers and freezing winters. They’re stuck in a tough spot for growing grass: Northern-bred cool-season grasses burn out in summer, while Southern-bred warm-season grasses freeze off in winter.
What Is the Transition Zone?
Grass-growing choices are relatively easy in much of the United States, who live in one of the five well-defined turf-growing regions:
- The cool, humid Pacific Northwest coast.
- Another cool, humid area covering the Midwest and Northeast.
- The cool, arid area spanning the Intermountain West and much of the Great Plains.
- The warm, humid Southeast.
- The warm, arid Southwest.
The first three grow cool-season grasses; the latter two grow warm-season grasses.
The problems arise trouble arises in the northern South, and the southern North: the transition zone. It overlaps the central portion of the country, overlapping four of the five turfgrass-growing regions from the Atlantic Coast to eastern New Mexico. The area’s mixed climates present the greatest grass-growing challenges.
Struggles of Growing Grass in the Transition Zone
Homeowners trying to maintain a lawn in the transition zone face climates that blend northern and southern weather patterns. They make it hard to select the “right” grass for their area. In the transition zone, the weather is too cool in the winter to maintain warm-season grasses, yet warmer summer temperatures make growing cool-season grasses difficult.
Unlike Goldilock’s porridge, the temperature in the middle is never “just right.”
Read up on the topic and you’ll find optimists vehemently saying you can grow either warm-season grass varieties or cool-season grasses — with some extra work and acceptance your lawn may not be perfect. On the flip side are those with an outlook similar to a glass half-empty. They express the “lawn half-brown” attitude and say you can’t successfully grow either type.
There’s truth to both.
Warm-Season Versus Cool-Season
The challenge lies in that grass types are classified as either warm-season or cool-season, based upon the temperatures they prefer for optimum growth. The transition zone sees temperatures that don’t fit solidly into the classifications of either type of grass. This makes it so neither warm-season grasses nor cool-season varieties perform exceptionally well.
Warm-season and cool-season grasses demand slightly different growing conditions. Or as a plant biologist would say, they differ in their photosynthetic pathways. Hence it’s important to understand the different types when you are choosing a variety for your turf.
These varieties are typically grown in the southern parts of the United States, where daytimes temperatures are higher and winters are mild.
- Need a minimum air temperature of 60 to 65℉ and soil temps of 50℉ for growth to begin.
- Produce most of their biomass in the hottest months of July to September.
- Optimum biomass production when average temps are 85 F to 95 F.
- Have a greater photosynthesis rate at higher temps to better utilize nitrogen and phosphorus.
- Better adapted to high-stress situations such as drought, high temperatures, and high oxygen/low carbon dioxide concentrations.
- Go dormant and turn brown in areas with a cold winter.
Common warm-season grasses include:
- Bahia grass (Paspalum notatum)
- Bermuda grass (Cynodon dactylon)
- Buffalo grass (Buchloe dactyloides)
- Carpet grass (Axonopus affinis)
- Centipede grass (Eremochloa ophiuroides)
- St. Augustine grass (Stenotaphrum secundatum)
- Zoysia grass (Zoysia japonica)
These turfgrass types are grown in the Northern parts of the country where summer temperatures are cooler and winters may be harsh.
- Need a minimum air temperature of 40℉ to 42℉ for active shoot growth.
- Most of the biomass is produced in the spring and late fall when both air and soil temperatures are cooler.
- Optimum biomass production when average temps are 65℉ to 75℉.
- Require more water to stay green in a hot summer.
Common cool-season grass varieties include:
- Annual ryegrass (Lolium multiflorum).
- Creeping bentgrass (Agrostis palustris).
- Creeping red fescue (Festuca rubra var. rubra).
- Kentucky bluegrass (Poa pratensis).
- Perennial ryegrass (Lolium perenne).
- Tall fescue (Festuca arundinacea).
Picking a Grass Type for Your Transition Zone Lawn
When choosing a strategy or type of grass for growing a lawn in the transition zone it’s important to carefully evaluate some characteristics of your yard, weigh the pros and cons of each grass type, and talk to your neighbors to see what works well for them.
- Realistically look at the conditions in your yard. Check the soil pH, determine the soil type, and calculate sun exposure over the course of a normal day. If any of these parameters sway too far out of what is considered “good conditions” they need to be carefully factored into your decision.
- Look at the advantages and disadvantages of growing either a warm-season grass or a cool-season grass in your area. Think about the advantages are you looking for, and which disadvantages you find intolerable. What additional or ongoing maintenance practices can you tolerate?
- Lastly, talk to your neighbors, your county extension office and even local landscaping companies to get a better idea of what grass types work the best in your local climate. Personal recommendations are one of the best decision making factors.
Climate Change Scrambling the Choice
For a long time, most homeowners opted to go with cool-season grass varieties in the transition zone. The tradeoff: They had to provide extra maintenance to their lawns in the warm summer months. They found this path simpler than nursing a warm-season turf-type through a dormancy period experienced due to the cold winter temperatures.
As climate change occurs we are seeing a gradual increase in the average temperatures of the transition region. When this is paired with an improvement of the cold-tolerance of warm-season grasses, these warm-season varieties have become the more popular strategy as transition zone grass.
There are currently two types of warm-season grasses commonly grown in the transition zone: Zoysia grass and Bermuda grass.
- Require fewer inputs than cool-season varieties.
- Less expensive to maintain.
- More environmentally friendly.
- Suffer from fewer disease problems.
- Excellent heat and drought tolerance.
- Better adapted to withstand foot traffic in the warmer temperatures.
- Improved types show more cold tolerance.
- Subject to thinning by low-temperature kill during the first year of establishment.
- Loss of color in the winter.
- Cost of establishment is higher than cool-season varieties.
Ongoing lawn care maintenance chores:
- By overseeding, cool-season grass seed can be interspersed in an existing lawn to provide green color in colder winter months.
- Requires more frequent aeration or dethatching as these varieties produce more thatch from stoloniferous and rhizomatous growth habits.
Warm-Season Grasses Grown in Transition Zone
Zoysia grass is a top contender for lawn grass in the transition zone. Once established it creates a dense, high-quality turf that has excellent heat, cold, and shade tolerance, repairs itself as it grows, requires less water than other grass types, and needs less mowing. It survives farther north than Bermuda grass due to its improved cold tolerance.
- In northern areas of the transition zone (Missouri, Illinois, Kansas, Kentucky, Indiana, Ohio, Virginia, or Maryland) opt for the cultivars Meyer or Zenith.
- Farther south (Oklahoma, Arkansas, Tennessee, and North Carolina) choose Cavalier, Emerald, El Toro, Meyer, Zenith, Zeon, or Zorro zoysiagrass.
One of the most common warm-season grasses grown in the South, Bermuda grass works well in the transition zone, too, on both high- and low-maintenance schedules, depending on the usage.
Bermuda grass performs well in the more southern area of the transition zone; Yukon Bermuda grass and Riviera Bermuda grass are perennial in most parts of the transition zone. It will turn a brown color when it goes dormant in the winter since it is not as cold-tolerant as Zoysia grass varieties.
Cool-Season Grass Strategies
Tall fescue, perennial ryegrass, and Kentucky bluegrass are the three most popular cool-season grass strategies in the transition zone.
- Excellent cold tolerance.
- Great winter survival rates.
- Require more nitrogen fertilizer than warm-season varieties due to a longer growing season.
- Struggle to actively grow during the hot summer months.
- More prone to diseases.
- Extra irrigation needed in the hot summer temperatures.
- Increased disease and insect pressure, especially in humid areas.
Cool-Season Grasses Grown in Transition Zone
Tall fescue is known for being shade tolerant, drought-resistant, and maintaining its beautiful green hue throughout the entire year. Unlike other cool-season grasses, it performs well in the lower areas of the transition zone where the season is too hot for the other cool grasses and in the area of the transition zone that is too cold in the winter for the warm-season grasses.
Perennial ryegrass has adapted well into lawns in the transition zone because of its ability to grow quickly, generating what seems to be an instant green coverage. High disease and insect resistance make it a great option if you are looking for a low maintenance cool-season grass.
One of the longest living perennial cool-season grasses grown, Kentucky bluegrass has maintained constant popularity since it was first introduced to the United States by early Europeans. A tender bladed turfgrass, it’s known for a desirable “barefoot feel.” It has good lawn mending capabilities and is fairly easy to establish.