Graffiti is a problem against which cities often struggle in vain. Climbing trees and shrubs at the base of walls are a super solution -- inexpensive, easy to maintain, and environmentally friendly to boot. Already existing graffiti can, of course, also be covered. Read on to learn more and see some examples.
"An ounce of prevention is worth a pound of cure." Most of the plants will only protect the base area, and then regular pruning is necessary. Often certain wires, according to the cable systems 1020, 1060, or 8010, are required to reign in the stubborn instincts of some plants and affix them to the wall. An easy kit is usually sufficient for this. Also painted plants, i.e. floral motifs by artists, are an effective protection against graffiti; see below.
Sometimes it's already happened...
In order to protect the base of the wall after graffiti has been removed, roses and pyracantha (scarlet firethorn) can be planted. It's no fun in the dark for sprayers to run up against their sharp thorns that tear into expensive brand name apparel... Evergreens are also a good choice against graffiti. Small, low-maintenance winter creeper is another good option; it remains limited to the base areas with only moderate growth, yet requires little pruning.
The removal of graffiti is expensive, and stucco or protective coatings may be removed with the grafitti in the process. This could hinder the water vapor permeability of a wall, which in turn can lead to delamination/spalling in certain kinds of masonry. Therefore, it may be useful to leave graffiti on the wall, and to conceal it by greening over it. Ivy, Virginia creeper, and Boston ivy can rapidly green up a grafittied wall. Careful though-- overgrowth can possibly lead to structural damage.