June brings the late-spring-to-early-summer transition, the longest days, rapid growth, and early flowering in gardens. Bird migration and insect emergence lead to nesting among and feeding on native plants. Pollinators become active in their flight seasons as populations build up. In the garden, we often notice flower color, diversity, and phenology (bloom timing) throughout the season. Less showy grasses and sedges may draw less attention, yet they are key elements in natural areas and gardens, providing structure, texture, color, and habitat.

Planting grasses and sedges as a “matrix” will physically support other plants that grow with them. Using them a dense groundcover, their stalks and leaves shade bare soil and their root systems hold soil, preventing erosion and promoting infiltration. These matrix plants vary in leaf blade thickness, with leaves held vertically, like prairie cordgrass (Spartina pectinata), or arching, like prairie dropseed (Sporobolus heterolepis). During early summer, plant form (rhizomatous or bunchgrass) and subtle color differences (e.g., bright green or blue green) may help in identification. It may be difficult to determine the flowering height of grasses that are only in vegetative condition this month, but that information is available in guidebooks and seed and plant catalogs.

Cool season grasses grow best in spring and fall. Native species blooming in June include blue-joint grass (Calamagrostis canadensis) and Junegrass (Koeleria macrantha). The former is a three-to-four-foot tall rhizomatous species suitable for sites with intermediate soil moisture like rain gardens; the latter reaches 18 inches (in bloom) on dry rocky soils or in rock walls. Other cool season grasses include Canada rye (Elymus canadensis), silky rye (Elymus villosus), and bottlebrush grass (Elymus hystrix). These reach three feet in height and are best suited for semi-shaded sites.

Native grasses provide a food source for skipper butterfly larvae and other insects, seed sources for songbirds, and cover for wildlife. Bunch grasses provide shelter, nesting sites, and winter food under the snow.

Weedy non-native cool season grasses like bluegrass (Poa spp.) and quack grass (Elymus repens) may be found in native plantings. We mainly see (and remove) them in areas where their rhizomes were not eliminated completely during site preparation. Our professional crew applies prescribed fire to some garden areas (for example, the parking circle garden) in March and April. This sets back cool season grasses while stimulating warm season grasses and other plants. Cool season grasses may persist in home gardens because prescribed fire cannot be used safely near buildings.

Native sedges that bloom by June can also be grown as “matrix” plants. Versatile species for semi-shade include rhizomatous Penn sedge (Carex pensylvanica), as well as several with a clump form: rosy sedge (C. rosea), eastern star sedge (C. radiata), and long-beaked sedge (C. sprengelli). Many other species are available to match the conditions of your site.

Enhance your early summer garden with hardy and easy-to-grow native grasses and sedges.

– Susan Carpenter, Native Plant Garden curator