Grasses vs. Sedges

Text and photos  by Elaine Mills, Certified Master Gardener

Sorghastrum nutans (Indian grass) - Fall foliage

Sorghastrum nutans (Indian grass) – Fall foliage
Photo © Elaine Mills

To prepare a public education presentation I gave last fall on native grasses and sedges, I educated myself about the general physical characteristics of these plants. Here are some of the interesting facts I took away from my research.

Grasses and sedges are both classified as monocots. These are plants whose seeds have one cotyledon (the part that will grow into embryonic leaves), and which possess flower parts in multiples of three, leaves with parallel veins, and scattered vascular bundles.  While they resemble each other superficially, grasses are members of the Poaceae family and sedges belong to the Cyperaceae family.

Grasses can be annuals or perennials, and they are further categorized as either cool or warm-season plants. Cool-season grasses start growing early in the spring, and develop slowly during the period of cool weather and rain. Their foliage is  most luxuriant in the late spring and summer, after which they go dormant. Warm-season grasses grow rapidly only after daily temperatures reach 60 to 65 degrees. They develop foliage in the summer, flower and fruit in the fall, and go dormant after the first frost. Both types need to be cut back  to short clumps of two to five inches in early spring before new shoots emerge. Grasses are naturally abundant in dry, open environments, such as meadows and prairies, where they provide habitat for feeding, nesting, and sheltering wildlife, although some  prefer shadier woodland settings.

Sedges are primarily perennials, and are mostly evergreen, cool-season, shade-loving plants. They generally prefer moist to wet environments. While more diminutive than many grasses, sedges provide support to a variety of animals. Local native sedges belong to the genus Carex, at around 2,000 species, one of the largest plant genera on earth.

The stems of grasses are hollow and either round or flat  with swollen nodes or joints along the stems. Their leaf blades are flat and their leaf sheaths are open. The stems of sedges, on the other hand, are generally solid and triangular (note the mnemonic “Sedges have edges”). Their leaf blades may be folded, and the base of each leaf is closed around the stem.

The leaves of grasses are said to be “two-ranked,” meaning they grow in two rows on opposite sides of the stem. The leaves of sedges are three-ranked and are arranged spirally in three vertical planes along the stem.

Grasses grow both vegetative and floral stems, and many of their wind-pollinated flowers are showy. Grass fruits are seeds, and are covered by two papery scales. Sedges produce only floral stems, and their wind-pollinated flowers tend to be inconspicuous. Sedge fruits are nutlets, and are enfolded by a single scale.

Examples of sedge flower stalks, Carex pensylvanica and Carex plantaginea

Examples of grass flower and seed heads

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Grasses grow in ever-increasing tufts; the new shoots they send out are called tillers. The fibrous roots of grasses can measure 6 feet  or more in depth, allowing them to absorb water and minerals and stabilizing both the plant and the soil. Sedges are clump-forming, and they spread laterally via rhizomes that are also useful in erosion control.

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