The Ostrich Fern, Matteuccia struthiopteris, is a popular plant chosen for shaded gardens. Gardeners frequently question its classification due to its vigorous spreading habits. This plant is not considered ecologically invasive in North America because it is native to the continent. However, the Ostrich Fern is accurately described as highly aggressive in a garden setting, quickly colonizing any area where conditions are favorable.
Defining Aggressive Growth
The distinction between an invasive species and an aggressive one rests on the plant’s origin and its impact on the natural ecosystem. An invasive plant is non-native and causes demonstrable harm, often displacing native flora. Since the Ostrich Fern is native to North America, it cannot be invasive in its native range.
The plant’s aggressive behavior is driven by asexual reproduction. It spreads rapidly through creeping underground stems known as rhizomes. These rhizomes extend horizontally outward, often a foot or more per growing season, forming new crowns and colonies. This network allows the fern to quickly establish dense patches that crowd out less vigorous garden plants. This vegetative propagation is significantly more effective for colonization than its sexual reproduction through spores.
Identification and Native Habitat
The Ostrich Fern is identifiable by several distinct features. Its most recognizable characteristic is the vase-like, or shuttlecock, arrangement of its fronds that emerge in a circular crown. These sterile, feathery fronds can reach an impressive height of up to six feet in optimal conditions.
The plant produces two distinct types of fronds. The large, arching, green fronds that give the plant its height are the sterile fronds, which die back in the fall. In contrast, the much shorter, darker brown fertile fronds emerge later and remain stiffly upright through the winter.
The Ostrich Fern is native across the circumboreal region of the Northern Hemisphere, with the North American variety found widely across the northeast and parts of Canada. It naturally thrives in environments with rich, moist soils found along riverbanks, floodplains, and in shady, lowland forests.
Controlling Unwanted Expansion
Managing the aggressive spread of the Ostrich Fern requires proactive intervention focused on its rhizomatous growth habit. One effective method for long-term containment is installing a physical root barrier around the planting area. This barrier, made of durable material like plastic or metal sheeting, must be buried vertically in the ground.
The barrier should extend to a depth of at least 12 to 18 inches to effectively block the creeping rhizomes. For existing colonies that are too large, regular division of the clumps is necessary to control size. This involves digging up the entire clump and using a sharp spade to cut away sections of the root mass.
Gardeners must also routinely monitor the perimeter for new, small crowns emerging from the runners. These new plants, often called “baby ferns,” can be easily removed by hand or by cutting the connecting rhizome with a sharp shovel. Growing the fern in a large, sunken container can also be an effective strategy to keep the runners contained.