I have two major problems in my garden, ivy and a weed I didn't know in NZ, but here it is referred to as wild fig. It is not a fruiting plant, but looking at my real fig tree I can see where the name might have come from.
Stone walls here are made with the dry stone method, now a dying art. Looking at one of these walls in good condition (ie, not attacked by the two plants mentioned above) you simply can't tell if the wall has been there for three hundred years or one thousand years. They are quite amazing. (This town was established in 904AD, so I don't jest about 1000 years).
My terraces have such walls. This is where the bigger problem becomes my problem. I have sections of wall (some shared responsibility with neighbours) where the two plants have taken hold. Local lore is that the roots of these plants are needed to hold the rocks together, but the same person who told you that could well tell you, the following day, that the plants are destroying the wall.
This conflicting advice seems to me to have come from nature. We have massive rocky hills (mountains in fact) around us. The trees and shrubs to grow into these. Then fire comes through, too often and too close for comfort, and the vegetation is destroyed. The next wet and soggy winter the roots of the plants rot away, and the rocks loosen. Boulders come tumbling down when the weather is stormy, occasionally bouncing onto houses, cars, and on one occasion killing a young man. Luckily all these danger areas now have huge wire nets and fencing to protect us. (I remember, prior to this, writing to my family that should I be squashed by one of these boulders while out walking to just think "she was happy to go this way"). I've always had a "thing" about stones and rocks, love them!
Anyway, my observation is that, properly maintained as in free from intrusive plants, these dry-construction walls do literally look unchanged for centuries. The evil intrusive weeds must go!
This post is mostly in response to Helen who asked me for a photo of my stone wall on the vege gardening page where I asked for advice about getting rid of ivy.
Helen, here are the photos.
The wall in un-abused state; I have no idea how old it is, but as a rough guide for guesses, the house was last renovated in 1911. But it could be 500 years old too, like the stonework in the cantina of my ground floor apartment.
Today I am grateful for a willing helper.