Our neighbours have built up a flower bed and planted trees and shrubs against our boundary wall without our permission, the plants are preventing me maintaining it.
Most people put trees and shrubs up against boundary walls and stick trellises and the like on to them without even considering the question of ownership. In most cases there’s no harm done, but if you need to carry out maintenance to the wall you can ask your neighbour to remove the foliage to allow you access. If they’re being particularly difficult you can go to court for permission to go on to their land to carry out maintenance to your property but most of these disputes are best resolved over a cup of tea if at all possible.