Understanding the distinction can improve your designs
Confessional moment: I am a grass freak. Of the vast universe of plants I adore, ornamental grasses are among my favorite plants to design with. No other plant expresses the ephemeral and sensory beauty of a garden like grasses. They catch light like a stain glass window, rustle with the slightest breeze, and glisten with the morning dew. Grasses are a wonderful and sustainable addition to any border, yard, or planting. But there is one pitfall to designing with grasses that almost no one mentions: understanding the difference between warm season grasses and cool season grasses.
Before a garden book seduces with you photos of a grasses glowing in the sun, you really should understand how to use warm season and cool season grasses in a designed setting. I’ve learned the hard way. Some of my biggest planting fiascos resulted when I failed to pay attention to this distinction. Here’s what you need to know.
Gardeners frequently call anything that looks grassy a “grass.” True grasses are members of the Poacaea family. Other grass-like plants include the popular Carex genus (Cyperaceae), rushes (Juncaceae), and cattails (Typhaceae). But none of these are true grasses. Horticulturists divide true grasses into two general categories that describe their growth cycle through a year: cool season and warm season grasses.
|Cool season grass Nasella tenuissima "browns out" in the heat and creates a lovely effect.|
Cool season grasses start their growth early in spring and continue that growth while cool temperatures and rain prevails. When summer gets hot, these grasses typically go dormant, often “browning out.” Some cool season grasses even die back in the summer, leaving seeds to germinate during the next cool season. If you’ve ever seen your lawn covered in Annual Bluegrass (Poa annua) in May only to see it disappear by June, it’s because this is an evolutionary strategy devised by this cool season grass. Cool season grasses are best planted/seeded in early spring or late summer/early fall. They tend to germinate and establish quickly. Cool season grasses foliage color looks best during late spring and early summer.