Smooth Brome

Smooth brome (Bromus inermis) is an attractive plant, 18 to 48 inches tall and growing upright. It produces numerous leaves, alternating in position up the stem. The leaves are 4 to 16 inches long and 1/4 to 1/2 inch wide. The flat leaf blades grow from round, waxy, veined sheaths with a covering of soft hair. The blades themselves, however, are hairless and appear grayish-blue on the top and green on the bottom. The margins are rough. Note the W-shaped constriction on the blade near the tip—this is a reliable characteristic for identification.

The inflorescence is a drooping panicle with branches growing in whorls. Each branch has several roundish spikelets that mature to a beautiful rich purple color. The spikelets are 3/4 to 1 inch long and contain 7 to 10 flowers.

Smooth brome seed is flat, smooth, and brown. It is typically around 1/3 inch long. Most of the seeds do not have awns, but some may have very short awns.

This species has an extensive root system and produces many rhizomes.

Distribution

Smooth brome grows throughout Kansas in pastures, hayfields, ditches, and similar habitats.

This plant can tolerate a wide range of soils. It grows the best on deep, fertile, well-drained sand loam or clay loam, but can handle shallow or slightly saline soils well. The main need is for good drainage. Its pH preference is near neutral, but it can tolerate any pH above 5.5.

Smooth brome thrives best in full sunlight.

Life Cycle

This species is a perennial cool-season grass. It is one of the harbingers of spring, starting growth well before many other species (March in Kansas) and growing rapidly as the season progresses through May and even into early June.

Smooth brome flowers from May through July, finishing just before the hottest, driest part of the summer. It goes semi-dormant at this point, waiting for the days to cool off again before resuming growth.

How much smooth brome grows in the fall depends on the weather. Provided that drought conditions do not persist, this plant will begin growing again in September and will persist all the way into November. Smooth brome is one of the last grasses to go dormant at the end of fall.

Ecology

Smooth brome was introduced the United States from Eurasia, particularly Hungary, in the 1880s. It was widely grown in until the early 1900s, when its popularity waned. Its drought tolerance brought it renewed favor during the Great Depression. Now it is a naturalized species.

This species can be an aggressive invader, gaining a foothold in disturbed areas, spreading rapidly through seeds and rhizomes, and sometimes displacing native grasses. It frequently starts its progress from a ditch or waterway and goes on to spread across pastures that have been overgrazed or insufficiently burned.

As a cover for wildlife, smooth brome has mixed usefulness. It provides good shelter for nesting ducks and northern harriers. However, its tendency to mat makes it an entanglement to grassland bird species. Smooth brome is grazed by geese and small rodents.

Uses

Smooth brome is an important cool-season pasture plant in eastern Kansas, with some degree of success in other parts of the state, as well. It is nutritious and palatable to most types of livestock, with high yields that permit higher stocking rates when managed well. However, it can be rather frustrating to establish because, while it seems to have an uncanny knack of invading where it is not wanted, it readily surrenders to weeds, diseases, and grasshoppers where it is wanted. To ensure pasture-seeding success, start with a firm, moist, fertile seedbed with an optimal pH and no known weed seeds. Existing weeds should be destroyed by discing or tilling at the end of summer. Plant in late summer or fall at a rate of 20 pounds of pure live seed to the acre, using a drill adapted to native grass planting. Seed at a depth of 1/4 to 1/2 inch. During the establishment phase, do not allow any grazing on the stand, and mow at a height of four to six inches to keep weeds in check. If the smooth brome takes to the pasture well, it can be grazed lightly the following year. For established pastures, set up a management-intensive grazing system that involves heavy stocking in the spring, switching to warm-season pasture in the summer while the brome goes to seed, and a return to brome at moderate stocking rates in the fall. Always allow smooth brome to reach 10 inches in height before grazing, and always leave a stubble of four inches, giving each paddock about a month to rest between grazing periods. Prevent weed invasion by regularly mowing the edges of the pasture. Note that smooth brome has a tendency toward sod-binding, in which the plants crowd so thickly that none of them can thrive. An existing sod-binding problem can be corrected by grazing and burning to remove grass litter, but it can be avoided entirely by adding legumes to the pasture seed mix to ensure adequate levels of nitrogen.

As a hay or silage plant, smooth brome is a common choice because it is nutritious for livestock. However, a smooth brome hayfield is difficult to manage because the plants recover poorly from cutting. Smooth brome is most likely to succeed in the hayfield when irrigated. Careful attention must also be paid to soil fertility and to the time of harvest. The best way to balance the needs of the plant with the needs of the livestock is to cut from mid-May through the end of the month, after the early heading stage but before full bloom. Never graze smooth brome before cutting it, and never cut below a stubble height of four inches.

The tough roots and rhizomes of smooth brome make it a good candidate for erosion control. While it does well in the traditional erosion control settings of waterways and damaged areas, it also shows great potential for growing in orchards and walnut plantings. Smooth brome will perform best in areas where the annual precipitation exceeds 20 inches. Where the rainfall is lower, this grass will require irrigation to perform its erosion-control duties.

Hazards

Smooth brome is rather invasive, making it a poor choice for wildlife plantings. For those who want to eradicate this plant, burn in the spring when the brome is 4 to 10 inches tall, while there is still enough dry fuel present to make burning possible. Burning at this critical life stage of the plant will do it severe damage and give native warm-season grasses a foothold. Never burn smooth brome while it is dormant, or it will start growing aggressively.

In areas where smooth brome is abundant, its pollen can be a moderate allergy risk.