The Asparagus densiflorus, commonly known as the Asparagus fern, is a popular choice for both indoor containers and outdoor groundcover. Despite its common name and fine, feathery foliage, this plant is not a true fern; it is a member of the Asparagaceae family, related to the edible vegetable asparagus. What appear to be leaves are actually flattened, leaf-like stems called cladodes, which give the plant its characteristic airy appearance. Its potential size depends heavily on its growing environment.
Maximum Growth Potential
The final size of an Asparagus fern is highly variable, depending on whether it is grown in a pot indoors or allowed to spread freely outdoors in a warm climate. As a houseplant, the fern’s size is typically contained, reaching a height of about two to three feet with a spread of three to four feet. In optimal outdoor conditions, the trailing stems can reach up to six feet in length, allowing the plant to spread across a substantial area as a dense groundcover.
Growth habit is also differentiated by cultivar, which significantly influences the size and shape. The popular ‘Sprengeri’ variety exhibits an arching and spreading habit, often growing one to two feet tall while spreading three to four feet wide. Conversely, the ‘Meyersii’ variety, known as the Foxtail fern, has a denser, more upright growth pattern, resembling a stiff plume. This upright form generally remains more compact, usually reaching about two feet in height with a spread of two to four feet.
Environmental Factors Determining Size
The size a fern achieves is a direct result of environmental conditions that either encourage or restrict its natural growth vigor. The plant will not reach its maximum potential size if its extensive root system, which includes creeping rhizomes and fleshy tubers, becomes constrained. Growing the fern in a container that is too small forces the plant into a root-bound state, restricting the production of new top growth. The strong, tuberous roots can even exert enough pressure to crack or break weaker pots.
Light exposure is another determinant of biomass accumulation and density. Asparagus ferns that receive bright, indirect light tend to produce denser, more robust growth, leading to a larger plant. Plants placed in low-light conditions often become leggy, with sparse foliage and elongated stems, resulting in a less substantial size. Consistent access to water also supports robust growth, though prolonged water stress will limit the plant’s ability to produce new growth and reach its full potential.
Managing Overgrowth and Spread
Gardeners who need to maintain a specific size for their container plant or manage an outdoor spread must employ regular management techniques. Pruning is the primary method for maintaining a desired shape and limiting volume. This process involves cutting back the individual stems, or canes, at the base of the plant to remove older, yellowed, or excessively long growth.
For container specimens, division and repotting are necessary steps to manage size restricted by root growth. Every few years, especially when the roots are tightly packed, the plant can be lifted and divided into smaller sections. During this process, trimming the dense root mass and removing some of the water-storing tubers helps to reduce the plant’s vigor. The plant can then be repotted back into the same size container with fresh soil, effectively keeping the overall size in check.