Ferns contribute to a lush and exotic atmosphere in the garden. Ferns, once given ideal growing conditions, rapidly spread, forming a dense, green mat of fronds. Some growing conditions are so ideal that certain species of fern can outgrow the garden, taking over significant sections of yards and woodlands. Chemical herbicides are an important part of controlling invasive ferns.
There are many species of exotic ferns that have been introduced to gardens. Some, after introduction in gardens, have escaped their boundaries and become naturalized, taking over wide swaths of land, particularly woodlands. Other species have been intentionally introduced for erosion control. Property owners wanting to take back their gardens, or re-introduce native species, will need to get rid of these invasive ferns.
Several invasive species of fern can be found on North American properties. Bracken fern (Pteridium aquilinum), which grows throughout North America, spreads quickly by underground rhizomes. New York fern (Thelypteris noveboracensis), native to the Northeast, can be aggressive, also because of its far-reaching rhizomes. Boston fern (Nephrolepis exaltata) can become naturalized in USDA zones 9 and warmer. In Florida, the Old World climbing fern (Lygodium microphyllum) and the Japanese climbing fern (Lygodium japonicum) both become invasive, climbing up structures and woodland trees.
Success in eradicating invasive ferns by mechanical removal of plants is sketchy. However, it is worth a try in controlling small areas of ferns in the home landscape. Yank ferns out of the ground, doing your best to remove as much of the rhizomes as possible. Mulching after removal will help keep spores from germinating in the area.
For problem areas with invasive ferns, most homeowners will find that chemical treatment is necessary. Use a broadleaf herbicide containing glyphosate (found in Roundup) for best results. Apply in spring and early summer when ferns are actively growing. Avoid getting glyphosate on desirable plants, which will be damaged or killed by the chemical.
It may take several applications of glyphosate to kill ferns to their roots. Reapply as the plants die down and new shoots arise. Pull new ferns that sprout from spores in the yard or garden. Inspect the area the following spring and apply the herbicide if necessary. Planting cleared areas with native plants, well adapted to the local environment, will help control exotic ferns in the future.