Wednesday, February 26, 2014

Ripe for Discussion: Vines on Walls?

Ivy covers a structure in Kurashiki, Japan. Photo by Joel Abroad.
There may be a building under there somewhere....
Ivy covers a structure in Kurashiki, Japan.
Photo by Joel Abroad

I recently came across this study (published nearly four years ago, but new to me) from Oxford University in the UK saying that ivy could benefit walls by protecting them from temperature extremes and pollution.

I'd say there are at least two important caveats to this study:

1) The authors seem comfortable claiming ivy helps protect intact walls, but they note that ivy might exacerbate problems in walls that already have cracks or holes.

2) The ivy study seems to have focused only on five sites in England, so it's not clear whether the findings apply in much hotter/colder/drier/wetter settings. (Although really, is there any place wetter than England? Probably not this winter.)

What do other Internet sources say?

Today's Homeowner pretty much agrees with the Oxford study, saying ivy can protect "solid, well-constructed masonry walls" but basically warning against using ivy as a climber anywhere else -- dry-stacked walls, old brick homes, wooden walls or fences, siding, stucco, painted surfaces, etc.

The consensus on one home improvement forum (StackExchange) seems to be that ivy on walls is bad news. The only dissenters were the ones who cited the Oxford study.

And then there's the whole issue of invasiveness, at least here in the States (since the commonly used English Ivy, Hedera helix, seems to have been introduced here from Europe and western Asia).

As I understand it, ivy grown as a groundcover can be annoying in terms of running rampant over anything else in a garden bed, but it only really becomes invasive when it is allowed to climb, flower and produce seeds that are then dispersed by birds into forest settings. Seems like wall-grown ivy would be a constant source of menace in terms of introducing ivy seeds into the environment.


But even if you swear off English Ivy, what about using other vines - perhaps native vines - to cloak your walls? For example, what about letting the native Crossvine (Bignonia capreolata) clamber up your wall? Does the idea intrigue you or you terrified that tendrils will creep into your attic one dark and stormy night?

Bignonia capreolata, Crossvine, "Tangerine Beauty" variety. Photo by Eran Finkle
Bignonia capreolata, Crossvine, "Tangerine Beauty" variety (may be a bit easier to tame than the species)
Photo by Eran Finkle
Or what about Virginia Creeper (Parthenocissus quinquefolia), also native to North America, but sounds far more rampant than Crossvine. The Lady Bird Johnson Wildflower Center says that Virginia Creeper climbs with adhesive disks rather than penetrating rootlets and thus does not cause as much damage to buildings as some other vines.

Have you -- or would you -- grow a vine on a wall of your house or other structure (garage, shed, etc.)? 

Or do you think that's just asking for trouble?

One other idea -- what about getting the aesthetic and protective benefits of a vine without the potentially destructive drawbacks? Old-House Online suggests building a trellis along a wall for a twining climber like wisteria or grapevine.

I like the concept, although I object to the wisteria suggestion. Japanese Wisteria and Chinese Wisteria are exotic invasives, and I believe even our native wisteria -- American Wisteria, W. frutescens -- would want to grow too big and heavy for a wall trellis. Plus wisterias have poisonous seeds, which I would argue mitigates against using wisteria in a residential setting.

But perhaps other twining vines -- e.g.,  Coral HoneysuckleArmand Clematis or the Hops vine (Humulus lupulus) -- would do the trick?

Clematis armandii in bloom. Photo by Ali Eminov
Clematis armandii in bloom
Photo by Ali Eminov

Update: Here's how Mr. Smarty Plants of the Lady Bird Johnson Wildflower Center sees the pros and cons of growing vines on walls.