There aren’t very many things that are one size fits all. This is true for grass in Oklahoma. We’re seeing more mixtures of cool-season grass seed becoming available that aren’t strictly blends of turf-type tall fescue. These mixes also include Kentucky bluegrass and perennial ryegrass.
Traditionally, turf-type tall fescues were given center stage when it came to turfgrass suitable for use in light to moderately shaded areas in the upper two-thirds of the state. While perennial ryegrass and Kentucky bluegrass weren’t recommended for use alone in 100 percent stands, they were occasionally suggested for use in mixtures with tall fescue to soften the overall texture of the turfgrass stand and to broaden adaptation through improved genetic diversity in the mix.
Research conducted at Oklahoma State University over the last couple of decades shows the successful stands are comprised of tall fescue, Kentucky bluegrass and perennial ryegrass. These mixed stands have proven to grow well. Tall fescue alone won’t produce a sod with suitable strength for rolling and shipping, so sod producers must use either nylon netting to hold fescue sod together or Kentucky bluegrass is added at the time of seeding the sod field and the underground runners of the bluegrass provide sod tensile strength to the product.
Each component of a cool-season grass mix brings strengths and weaknesses to the mixture. Tall fescue has better shade tolerance and better resistance to summer patch and dollar spot diseases than Kentucky bluegrass. However, tall fescue is a relatively coarse textured bunch-type grass that is more susceptible to brown patch disease and Rhizoctonia blight. Kentucky bluegrass is finer textured than tall fescue, better able to spread and fill in gaps in the turfgrass stand. Perennial ryegrass has perhaps fewer benefits to bring to the cool-season grass mixture than Kentucky bluegrass, but one can still make a case for its use in the mix. Perennial ryegrass is finer textured than tall fescue, but it is still a bunch-type grass. The disease spectrum of perennial ryegrass is about the same as that of tall fescue. However, perennial ryegrass is not troubled by summer patch or necrotic ringspot.
When creating your own mix, pick the best performing and most disease resistant cultivars within each turfgrass species being used in the mix. Also, it’s helpful to pick varieties that have similar color and growth rate so as not to develop a mixture that has contrasting components that may lead to a nonuniform appearance.
Mixing isn’t a cure-all for the wide variety of problems created by using cool-season grasses in Oklahoma. Also, mixing won’t overcome the problems on cool-season lawns created by mismanagement of turfgrass areas. There likely won’t ever be the perfect grass. However, cool-season grass mixes definitely should take center stage for use in lightly shaded turfgrass areas in Oklahoma.
David Hillock is a consumer horticulturist with OSU cooperative extension.