How Grasses Grow

Grasses fall roughly into three major groups: annuals, biennials, and perennials. Annual grasses live a complete life cycle in one year or one season. They emerge from seed, grow roots, stems, and leaves, flower, and die in one season. Most of our important food grasses are annuals. Annual ornamental grasses are often overlooked, but many of them are decorative and easy to grow.

Biennial grasses sprout from seed, grow through the season, over winter, and continue to grow into the next season, when they flower and die. Their life cycle is completed in two seasons.

Perennial grasses live and grow for more than two seasons. The most important ornamental grasses are perennials. Many perennial grasses are extremely long-lived, persisting for decades. They can be herbaceous, woody, or semi-woody. The largest group of woody grasses also happens to be the largest group of true grasses: the bamboos.

Many grasses are perennial in one climate and annual in others. Tender fountain grass (Pennisetum setaceum), for example, is a perennial grass in the mild Mediterranean climate of Southern California, yet it is considered an annual in the Pacific Northwest. Each grass has its own tolerance to cold and heat and reacts differently from one climate to the next. Often, as little as 20 miles may separate a climate in which a certain grass could only be considered an annual from a climate in which the same species is perennial.

Seasons of growth

Grasses are classified as either warm-season or cool-season species, depending on when they are in active growth. Warm-season grasses grow when temperatures begin to warm in spring. They flower and set seed in summer and fall, and become dormant with the onset of winter. Cool-season grasses begin growth in late winter or early spring. They flower from winter into early summer, and become dormant or slow-growing in summer: These grasses resume active growth when cooler temperatures return in fall. In areas with mild winters, cool-season grasses often continue growing all winter.

A grass's seasonal habit of growth is often related to the climate in which it originated. Species that are native to areas with dry summers, for instance, often become dormant during the hot months and resume growth when temperatures cool and fall rains begin. Those grasses that are natives of areas with cold winters go dormant in fall, waiting for the warmth of spring to begin growing.

These seasonal patterns can change, depending on different climates or conditions. Under normal conditions, a cool-season grass is dormant during the summer, an inherent defense against drought. But if you water regularly, some plants will continue to grow.

Warm-season grasses

Warm-season grasses grow best at temperatures between 80°F and 95°F. They grow vigorously from spring to summer, then flower and begin dormancy in fall. Most warm-season grasses, like the leaves on trees and shrubs, turn a different color in autumn. Every wonderful fall color imaginable can be found in these grasses. As winter approaches, warm-season grasses continue to change color, becoming completely dormant. The past season's growth-leaves, flowers, and stems-dries and blanches to tan, wheat, or white. These winter colors have their own subtle beauty and purpose in the garden. Many warm-season grasses are useful for attracting winter wildlife into the garden.
Dormant winter foliage of warm-season grasses usually persists throughout the winter. Often the combination of snow, wind, and rain knocks the dormant foliage to the ground, but some grasses are better at standing up to winter weather.
With the spring thaw, warm-season grasses once again begin growing. New shoots rise from the base, and the cycle is repeated. The emergence of the grasses truly announces the arrival of spring.

Cool-season grasses

Cool-season grasses grow best at temperatures of 60°F to 75°F. They begin new growth in fall and are some of the first perennials to bloom in the garden. Some are even winter-blooming. Cool-season grasses are often more moisture-loving than warm-season species. Their leaves are usually evergreen, and in winter may be highlighted with red, plum, purple, yellow, or brown. Many of these winter colors disappear when temperatures begin to warm and later spring growth over-takes the earlier foliage.

Growth habit

Two types of growth habits characterize grasses. Running grasses spread by creeping stems, forming dense mats. Many running grasses can be invasive. Clumping grasses grow in tufts, slowly increasing in girth. Both types have their place in the garden.

Running grasses

Running grasses are also called spreading or creeping grasses. They spread by means of aboveground stems called stolons or underground stems called rhizomes, structures that can be delicate and hair-like or thick and hard. (When running grasses are spread by rhizomes, they are also called rhizomatous grasses.) Given years of growth under ideal conditions, the mature rhizomes of grasses like prairie cord grass (Spartina pectinata) can require a backhoe to remove.
Many running grasses can be invasive. Those that spread by means of stolons root along the stems as they grow, forming a dense turf. Such grasses are often used as lawns. Ornamental grasses such as variegated St. Augustinegrass (Stenotaphrum secondatum 'Variegatum') and buffalo grass (Buchloe dactyloides), which grow by stolons, can colonize large areas.

Clumping grasses

Clumping grasses, which grow in tufts, are often called bunch grasses, especially by ranchers and range management specialists in the West, where these species are important forage grasses. Clumping grasses vary from the delicate little 2-inch mounds of bearskin fescue (Festuca scoparia) to huge plants like pampas grass (Cortaderia selloana). Some clumping grasses or sedges, such as Berkeley sedge (Carex tumuicola), can appear like a sod or turf if they are planted close enough to grow together.

Grass Form

Grasses come in many shapes and sizes. There are six primary categories used to define the shapes of grasses. These categories describe the form of the foliage, not of the flowering stems, or inflorescences, and apply regardless of the plant's height.

TUFTED

Usually spiky foliage or fine-textured with upright leaves arising from a basal clump. Example: Blue fescue (Festuca cinerea).

MOUNDED

Somewhat weeping; mounding foliage. Top growth covers lower leaves. Example: Black-flowering pennisetum (Pennisetum alopecuroides 'Moudry').

UPRIGHT

Erect. Foliage grows vertically in a uniform or even columnar form. Example: Cattail (Typha latifolia).

UPRIGHT DIVERGENT

Foliage grows up and out in an erect or stiffly ascending manner. Example: Blue oat grass (Helictotrichon sempervirens).

UPRIGHT ARCHING

Foliage ascends vertically then becomes fountain like at the top. Example: Silver feather maiden grass (Miscanthus sinensis 'Silberfeder').

ARCHING

Foliage arches up and out, in somewhat equal proportion. Example: Palm grass (Setaria palmifolia).