As tree canopies fill in, many lawns thin out. By May or June, many people go in search of a ground-covering solution for shade.
These solutions usually fall into three camps:
- Shade grass seed mixes (See our recent article on what happens when you try to grow grass under trees.)
- Ground covers for shade, including annuals, perennials, ornamental grasses, and moss
- Mulch around the trees.
If your inclination is to reach for a shade grass seed mix, keep in mind that slope, soil, tree species, and tree roots all play a significant role. Other groundcovers may be a better investment of time and money.
That aside, three grass species stand out in studies of long-term shade performance. For northern climates, they are supina bluegrass (Poa supina) and creeping red fescue (Festuca rubra ). For southern climates, it’s St. Augustinegrass (Stenotaphrum secundatum).
The presence of these grasses in a regional mix is probably a good sign if you have shade problems, but read on for some of the details. (And see notes at the end of this article on the value of using seed mixes vs. single species.)
Shade Grasses for Cold Winter Areas:
Supina bluegrass (Poa supina) is an Alpine native and is the newest to commercial trade. It was first introduced as a turf species in Germany during the 1970s. Michigan State University tested it during the 1990s for athletic fields and other environments.* Turf specialists found it capable of thriving in deep shade where the soil is moist. It is sometimes mixed with rough bluegrass (Poa trivialis), which is almost as shade-tolerant. If conditions are right, supina bluegrass will populate a deeply shady spot where other grasses fade after a few seasons.
Unfortunately, this species seems to have three drawbacks, noted both in research and informal conversations.
First, it is expensive at about $25 - $30 per pound. It is partially overcome by the fact that it usually only five to twenty-five percent of a seed mix.
The second drawback is its light color. Some newer varieties such as Poa supina 'Supranova' may overcome this.
The third is that it does not like hot, dry weather. It may go dormant for a time in summer, not unlike other cool season grasses. (On the flip side, it is reportedly one of the first grasses to green up in spring.)
One commercial mix to consider is Poa Supina Shade Grass Blend from OutsidePride.com, a mixture of supina and rough bluegrasses. Another online source is Seedland.com, which sells the seed as a single species and offers mix recommendations.
The second candidate for deep shade is creeping red fescue (Festuca rubra ), one of the "fine fescue" group of grass species. It's been used for many years in a wide variety of grass mixes. According to a USDA fact sheet on red fescue, there are 200 named varieties. Though fescues are usually classified as bunching grasses, creeping red also spreads by rhizomes. This spreading characteristic helps “knit” a carpet of grass and overcomes the bunching appearance of other fescues.
Creeping red fescue grows across North America except for south central U.S. and Florida. Some growers note, however, that it is not as cold tolerant as Kentucky bluegrass or creeping bentgrass and is best used in zone 4 – zone 8.
Shade Grass for Warmer Areas
St. Augustinegrass (Stenotaphrum secundatum) is a warm season grass suited for the southeastern U.S., south-central states, and California. While it is considered one of the most shade tolerant among warm season grasses, a University of Florida Cooperative Extension article notes that specific shade cultivars of St. Augustinegrass offer the best chance of success. (They mention 'Seville,' 'Delmar,' and 'Captiva.')
St. Augustinegrass is usually planted from plugs rather than seed, although seed has recently become available in trade.
Summary: If you want turf to thrive under and around trees, one of the most important factors is the grass variety itself. Supina bluegrass, creeping red fescue and shade cultivars of St. Augustinegrass offer advantages in the battle between tree shade and turf.
A Note on Seed Mixes:
A well-designed grass seed mix contains plants that complement each other in growth rates, appearance, seasonal performance, tolerance to foot traffic, mowing height, texture, color, and other characteristics. Mixes reduce the chance that an entire planting will fail. Over several years, the species best adapted to the spot dominates the planting while others fade away.
Shade mixes often contain perennial ryegrass, for instance, because it will grow the first year while other species are getting established. In following years, perennial ryegrass fades away, and other grasses fill the area.
Reference Note 1: MANAGING POA SUPINA SCHRAD. (SUPINA BLUEGRASS) IN MICHIGAN J.C. Sorochan, and J. N. Rogers, III. Dept. of Crop & Soil Sciences, Michigan State University