Laidback Gardener Tip of the Day

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Do Climbing Plants Damage Walls?

Boston ivy (Parthenocissus tricuspidata) growing on my house. This was year 3: the wall is now entirely covered.

Boston ivy (Parthenocissus tricuspidata) growing on my house. This was year 3: the wall is now entirely covered.

Some vines, such as Virginia creeper (Parthenocissus quinquefolia), Boston ivy (P. tricuspidata), English ivy (Hedera helix) and climbing hydrangea (Hydrangea anomala petiolaris), climb via adhesive pads or aerial roots, depending on the species. This allows them to climb even flat surfaces, such as a house wall. However, old gardening books long advised against allowing climbing plants to grow on houses under the pretext that they would “root into the mortar” and pull it out.

Today we know they don’t root into mortar. In fact, adhesive pads don’t root into anything: they simply cling to the outer surface of the surface they climb. This is also true of aerial roots: old beliefs to the contrary, aerial roots are a specialized type of root, nothing like the roots that grow in soil: they never turn into true roots that could “dig into the mortar”. Like adhesive pads, they always remain strictly limited to the outer surface.

It was also once believed that vines grown on walls could damage them through excessive humidity and it does seem logical that a wall covered in foliage would remain more humid than a wall exposed to the sun. However, climbing plants actually protect against excessive humidity by keeping rain off the wall to start with. Rather then resulting in excessive humidity that could damage the wall, vine-covered walls actually tend to remain at a fairly constant, safe level of humidity and this actually preserves walls.

It is interesting to note that, even as “experts” were advising against using climbing plants on buildings, there were always plenty of examples of them being used that way. And it was abundantly clear that walls covered with climbing  plants actually lasted longer – much longer, such as hundreds of years longer in some cases – than walls exposed to the elements.

We now know that, in most cases, climbing plants are beneficial to structures. Yes, they should be trimmed back if they start to invade windows or climb onto roofs, but they protect walls from what really does damage them: sunlight (notably ultraviolet rays), rain and air pollution.

Of course the type of wall is a factor. You should test the mortar on stone or brick walls to make sure it is solid. The old trick is to run a house key over the mortar and if it doesn’t crumble, all is well. It likely won’t crumble if your house was built since the 1930s, as modern mortars are much more durable than older varieties.

In the case of walls made of wood, the answer is not as clear. Initially, vines protect the wood and make paint last for decades, much more than paint on walls exposed to the elements. On the other hand, when paint peels, it is impossible to repaint a wall covered with plants. So, in the very, very long term, probably not during your lifetime, it may be necessary to remove the vines so the wall can be repainted.

You’ll hear that you shouldn’t grow vines on stucco walls, that they can pull off paint or even chunks of stucco when you remove them, but then… why would you remove them? After all, they’re making the wall last longer. So if your goal is to permanently cover a stucco wall with vines, go right ahead!

When it comes to vinyl or aluminum siding, the jury is still out. These products are fairly new (they only began being used after the Second World War) and theory has it that the weight of the vines could pull them off the wall. There are many cases where siding has been covered with vines for decades now and no damage has so far been reported. That’s probably because vines lignify (harden) over over time and actually end up supporting the wall and its coverings. Most older types of siding need to be replaced after 20 or 30 years and vines may well help them last twice as long. No one knows how long newer types of siding will last, with or without vines. Some are now offered with a lifetime warranty… but that means little, as the average installer doesn’t expect you to remember who installed the siding if there is a problem 40 years later, much less keep proof of the installation.

My 70 year old house is covered in wood. When we moved in 21 years ago, we repainted, then I planted Boston ivy on two sides of the house. Those sides have required no care other than an occasional trimming around the edges of the windows and under the eaves. The other two sides have been repainted once and need to be repainted again. I have already picked out the vines I’ll be putting in after the next painting session. My theory is that my vine-covered walls are good for at least a century… and if they do need to be removed for repainting after that, well, that will be someone else’s business!

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