Why we should never plant shrubs (or trees, or even climbers) close to walls

I get this a lot: I'm either asked to plant something right up against a wall, or I'm asked to find out why a plant, which has been planted right up against a wall, is failing to thrive. So what's wrong with planting against a wall, then? Firstly, foundations: when you go to dig the planting hole, you might find that the foundations extend a fair way sideways, underground. This applies to planting…