Six on Saturday: Poison Ivy


Poison ivy is not native here. Neither is English ivy. However, English ivy, Hedera helix, is an aggressively naturalized exotic species. Even after it had been designated as a voracious weed in the region, it was installed in some of the landscapes here many years ago. It is so common here now that we know it simply as the standard ‘ivy’. Algerian ivy was planted too, but it is not quite so aggressive.

1. English ivy grew up and over this abandoned building, and accelerated the deterioration of the old roof. It would be pointless to remove it now. The building will eventually be demolished.P00125-1

2. This building is not abandoned. No ivy was on this roof just a few days earlier. All this ivy did not grow up and over the building this aggressively since then, but fell from above. Surprise!P00125-2

3. The yellow pointer shows where the dead redwood trunk that supported all the ivy broke and dropped the whole mess onto the roof at the bottom of the picture. It is about thirty feet up!P00125-3

4. What a mess! This close up of the same broken dead redwood trunk shows another dead redwood trunk to the right, and a viable trunk with another dense ivy thicket in the background.P00125-4

5. Surprisingly, this is the worst of the damage. It was likely impaled by the rotten redwood trunk. The ivy likely stayed connected to the rest of the thicket long enough to slow the descent.P00125-5

6. Even after getting Ginsu with saws and shears, and getting bounce-house with debris, the pulpy redwood trunk and ivy was still a full load. That was a lot of weight to land on an old roof!P00125-6

This is the link for Six on Saturday, for anyone else who would like to participate:

Vines For Better Or Worse

90619thumbVines in the wild are downright exploitative. They do not support their own weight, so instead climb or sprawl over shrubbery and trees. Some are satisfied staying down below the canopy of the hosts who support them, as if aware that a healthy host will support them for a good long time. Many vines climb aggressively to the top and overwhelm their hosts, even if it eventually kills them.

There is nothing civil about the technique of the strangler figs, which incidentally includes two popular houseplants, fiddle-leaf fig (Ficus lyrata) and creeping fig (Ficus pumila). They wrap their hosts in networks of stems and roots that strangle the hosts as both the hosts and the clinging vines grow and expand. As the hosts die and rot, the vines develops into self supporting tree trunks.

That is how fiddle-leaf fig, as it is known as a houseplant, grows as a free standing tree rather than as a creeping vine. It is grown from cuttings from the self supporting adult growth rather than the creeping juvenile growth. Conversely, creeping fig is grown from juvenile vines, which find a support to cling to, and ultimately develop shrubby adult growth when they get to the top of the support.

English and Algerian ivies are not quite as aggressive, since they do not intend to kill their hosts. They are not often intentionally grown as vines, and are almost never planted anymore, but their juvenile growth still works as ground cover in many mature landscapes. One of the main problems with ivy is that it is constantly trying to climb walls and trees so that it can bloom and toss seed.

That is not such a problem on concrete walls, but ruins wooden and painted surfaces, and makes a mess of trees. Boston ivy (which is not really an ivy) lacks a juvenile ‘ground cover’ phase, but if kept off of painted and wooden surfaces, happens to work better on concrete infrastructures. It is important to know how a particular vine will behave before selecting it for a particular application.

Carolina jessamine, mandevilla, lilac vine and star jasmine are a few complaisant vines.

Vines Are Naturally Social Climbers

70906thumbIf more of us knew how vines compete in the wild, fewer of us would grow them in our home gardens. Understory plants that are satisfied with the sunlight that reaches them through a higher forest canopy are the most passive. Taller trees compete for sunnier exposure above. Vines are the most aggressive as they climb and overwhelm trees to get the best exposure on top of everything.

English and Algerian ivies happens to be among the more efficient of aggressive vines. While young, juvenile growth creeps along the ground searching for victims. Once it encounters something to climb, the stems develop aerial roots so that they can climb vertically. Once the climbing stems reach the top of the support, they develop shrubby adult growth that blooms and produces seed.

In home gardens, ivy is a popular and practical groundcover. However, if allowed to climb as a vine, it can root into walls and ruin paint. Even if the vines are removed, the unsightly aerial roots remain. The shrubby adult growth can overwhelm and even shade out and kill the trees or shrubbery that originally supported it. If it climbs onto a roof, it can accumulate debris and promote rot.

Creeping fig is even nastier. Its network of clinging vines grafts together as it grows, and then strangles the supportive trees as they continue to grow within the constrictive network of grafted stems. Yet, it and Boston ivy work nicely and harmlessly on concrete freeway sound-walls where their aggressive behavior is a major advantage, and their clinging aerial roots are not a problem.

Wisteria and red trumpet vine are considerably better behaved, but even they will crush lattice and anything else they wrap around. If they get into trees, they quickly grow out of reach. They may seem to be more appealing than the trees that they climb are, but can strangle and kill substantial limbs. Even without aerial roots, red trumpet vine clings with holdfast discs that damage paint.

Even though many vines are practical for home gardens, their personalities need to be considered. Star jasmine and honeysuckle can either grow as groundcover or as climbing vines. They can get big, but are not often destructive. Potato vine works nicely on fences, but gets aggressive in trees. Carolina jessamine, lilac vine and mandevilla are some of the more complaisant of vines.