We see them in nearly every New Orleans neighborhood — stoic but blighted houses so covered in vines that it looks as if the vegetation is supporting the building and not the other way around. In some cases, the greenery appears almost to be a kindness; helping to soften the harsh realities of neglect. Many times, the plants blossom with attractive flowers that brighten up the landscape. However, no matter how these plants may blur the line between beauty and decay, make no mistake. They are killers.
IVY (HEDERA), with its adventitious roots (those that grow along the stem and not from the base of the plant), is perhaps the most publicized home invader. The root hairs of ivy seek out moisture, insinuating themselves into cracks in mortar, plaster, and masonry. Over time, this growth pattern can widen the cracks and weaken the structure. Nevertheless, many people choose to enjoy the beauty of an ivy-covered building and ignore the risks associated with it.
Many other vines with adventitious roots exhibit similar characteristics. In warmer climates, both common U.S. plants (such as Virginia creeper, Parthenocissus quinquefolia) and “house plants” — tropicals that don’t survive the winters elsewhere — can be problematic. Philodendron and Swiss cheese vine (monstera delicious) are prime examples of house plants that are naturalizing in our climate. In the wild, these plants use long, adhesive aerial roots or tendrils to attach themselves to trees. Planted close to your house, those roots can sneak between weatherboards, eventually loosening them or causing them to rot from the moisture.
NOT ALL VINES send their roots into cracks and under weatherboards, but that doesn’t make them innocuous. In semitropical climates, one of the most prominent invaders is cat's claw vine (Macfadyena unguis-cati), a common sight growing on blighted buildings, fences, and other wooden structures. The vine, which is native from the West Indies and Mexico to Argentina (but not the U.S.), has three-pronged, clawlike climbing appendages that grasp other plants or surfaces.
Cat’s claw grows slowly up to 50 feet in length and produces both tubers and seeds for new growth. It creates a dense mat that on the ground smothers other plants and on a building retains moisture and blocks sunlight, creating a perfect environment for mold and decay. Cat’s claw also contributes the beautiful yellow flowers that decorate abandoned buildings. However, don’t let that beauty tempt you into encouraging it — anywhere.
The Center for Aquatic and Invasive Plants says there are no known biological control agents for many invasive vines. Furthermore, mowing — or even clearing — self-seeding vines such as cat’s claw and Virginia creeper will likely facilitate their spread. For cat’s claw and other self-seeding vines, the Center recommends cutting the vines and painting the ends with a 100 percent solution of glyphosate (sold commercially as Roundup) as a control. Glyphosate must be applied with caution as it is toxic to most plants, including beneficial ones.
For tropicals and plants that don’t self seed (check with your local AgCenter if you are uncertain), a good solution is to sever the vines from their root stock and then cut them into pieces. Wait for them to start dying, then carefully pull them away from the structure they cover.
SOME OWNERS of historic property allow flowering ornamental vines, such as Chinese Wisteria (Wisteria sinensis) or Hall’s Japanese honeysuckle (Lonicera japonica Halliana), to twine around their columns or ramble along their fences. Unfortunately, any vine that can wrap itself around structural elements, even if it doesn’t invade cracks or attach itself with adhesive, can be destructive.
In Historic Building Façades: the Manual for Maintenance and Rehabilitation, (New York Landmarks Conservancy), William G. Foulks describes how seemingly innocuous plants can damage a building. In addition to problems with moisture, Foulks notes, walls covered with foliage are more difficult to inspect for deterioration and as such may not receive necessary maintenance in a timely fashion.
Louisiana State University AgCenter Horticulturalist Dan Gill recommends gardeners avoid Chinese Wisteria and Hall’s Japanese honeysuckle entirely (not only for homes, but also for pergolas and other outdoor structures). He recommends native vines such as Coral honeysuckle (Lonicera sempervirens) or native maypop (Passiflora incarnata) and annual vines such as Alice DuPont mandevilla (Mandevilla x amoena) for outdoor structures instead.
Other safe and attractive (in many cases, exceptionally showy) recommendations, according to Gill, are akebia (Akebia quinata), red passion vine (Passiflora coccinea and P. vitifolia) and blue passion vine (P. caerulea), hyacinth bean (Dolichos lablab), cardinal vine (Ipomoea multifida), and moon flower (Ipomoea alba). However, all of these belong in the garden and not on historic structures. #ForumBulletin