Thursday, March 19, 2009

Amazing Ivy by Gardener Dave

Boston Ivy

Are you an “Ivy Fan”? I am – up to a point. I use English Ivy (Hedera helix) as a groundcover for shade and semi-shade, and Boston Ivy (Parthenocissus tricuspidata) as a wall climber/cover in sunnier areas. Ivies can be used to “soften” a bare wall behind other plantings and provide added cooling and humidity in our dry climate. They can help to alleviate scorching and discourage spider mite infestations in sunny walled areas.

Part of my fascination with ivy is its ability to cover large expanses of ground, walls or fences quite quickly. I also like the evergreen (depending on our winter) qualities of English Ivy, and I like the fall reddening of Boston Ivy. I am also fascinated with the clever means by which these ivies climb walls and other vertical surfaces.

There are many other “ivies” and climbing plants that use different means of attachment, such as tendrils which wind around any supporting structure (and itself) in order to reach and grow upwards. I am only detailing here the ivies with which I have had personal experience. I also have some Virginia Creeper (Parthenocissus quinquefolia) – also sold as Engleman’s Ivy – coming into my yard from a neighbor’s. It does turn red in the fall, and it is very hardy, but it can be extremely invasive, and it is susceptible to powdery mildew which can spoil the fall color. Of the three types, English Ivy is the only one that is “evergreen” here (* See “Cautions” below).

In 1865, Darwin wrote about ivy at length in his book The Movements and Habits of Climbing Plants. The following are some of my own observations: My English Ivy has little “rootlets” that grow sideways from the main stems and take advantage of any little spaces on brick or stone walls, fence slats (or almost anything) to wedge itself in. The “rootlets” also adhere to surfaces very tenaciously. My Boston Ivy has little “feet” or “hands” growing from the main stems (please excuse my not using botanic terms for these appendages). Each “foot” has several little separate sticky pads that can seemingly attach to ANY surface with an extremely strong glue-like bond. They even attach to undersurfaces such as eaves and patio ceilings!

English Ivy

Geckos are famed for their ability to walk on walls, thanks to nanoscopic hairs on their feet called “setae”. http// Ivy uses another nano-scale trick to defy gravity. Several articles I have read lately describe an exuded form of “nano-sized [cementing] globules” that allow ivy to cling tightly to surfaces. Researchers at the University of Tennessee in Knoxville have studied the process in depth, and say their tests reveal something like 19 different primary compounds in the ivy bonding process. I promise I won’t go into the chemical analysis of their research, but they report that millions or even billions of weak adhesion or hydrogen bonds (not bombs!) that the ivies produce, add up to make a very strong adhesion to climbing surfaces.

Researchers are also working on ways to counteract these forces with the goal of making paints that can protect surfaces from ivy damage. Also, researchers at University College Dublin in Ireland think that “…studying plants like ivy could uncover entirely novel nano-materials.” Perhaps new “miracle” adhesives?

Cautions: My ivies are not parasitic; they do not obtain nourishment from the trees, etc. that they climb on. But they will take advantage of any surface they can get their little “rootlets” into, “sticky pads” onto, or “tendrils” around. My ivies climb my brick house walls and fences and trees in my yard. They can also creep into windows and between (fairly tight) window panes. It looks “quaint” on a house wall and adds green interest to the overall landscape, but if you want to remove it, it can pose some problems. In our dry climate, the problem takes the form of leftover adhesions when you pull it off. A paint scraper or similar tool can help remove them, but they will never come off 100% unless the surface is vigorously sanded. Also, (*) English Ivy may winterburn in more-exposed areas, losing attractiveness and requiring some trimming back in Spring.

By way of interest – in moist climates, large overgrowths of ivy can bring down weakened tree branches, and its long-term decay against brick or stone walls can form humic acid which is capable of dissolving carbonate stone and some mortars. I seem to remember reading where some ivies are considered noxious weeds in moist climates, but in our area this should not be a problem with the three types I have mentioned.

Virginia Creeper

So – as I said earlier – I am an “Ivy Fan” up to a point. If you are willing to cut them back when you need to, they can be a nice green addition to your landscape. Don’t let them become too invasive, especially the Virginia Creeper or Engleman’s varieties. I have learned my lesson. Use them with this in mind and you will be happy with them. They are interesting, useful and decorative plants.

Gardener Dave