This section is from the book "The Gardener's Monthly And Horticulturist V23", by Thomas Meehan. See also: Four-Season Harvest: Organic Vegetables from Your Home Garden All Year Long.
This question has been many times proposed and considered. In my monograph on "The Ivy," I have treated it at some length, and with the aid of evidence adduced in an important inquiry as to the effect of ivy on the fabric of English churches. My friend M. Sisley, of Lyons, informs me of neighbors of his who actually dread to plant ivy near the walls of their dwellings, from the apprehensions they entertain of consequent damp and injury to the structure. So long as such opinions prevail it cannot be too often repeated that the attachment of ivy to walls is an advantage altogether. If the walls are damp before the ivy is planted, the damp will disappear as the ivy overspreads their surfaces. If the walls are dry to begin with, ivy will keep them so, by a double action; for should dampness occur through some accident, the ivy will suck out the moisture into its own substance, and in the event of driving rains, that occasionally act with force on walls, the imbrication of hard leafage will prevent the access of rain to the structure, and thus ivy is not only a remover, but a preventer of damp. As regards the integrity of the structure, however, the case is less clear.
Fissures in walls clothed with ivy will sooner or later be discovered by the plant and rilled up, and then mischief may be expected. When a shoot or root pushes through a fissure in a wall and is left undisturbed, its natural growth soon begins to tell upon the structure. As the little nut tree carried the millstone, so the slender shoot of ivy will by increase of girth begin to push against the sides of the fissure, with the certainty of increasing it, and the probability of bringing the wall down. But where the wall is sound it is exposed to no such danger. Ivy does not make fissures, however quick it may be to discover them where they already exist. It follows therefore that, as a rule, ivy may be regarded as defending against time and accident the walls that afford its support. - Shirly Hibberd.