This section is from the book "The Gardener V1", by William Thomson. Also available from Amazon: The New Organic Grower: A Master's Manual of Tools and Techniques for the Home and Market Gardener.
Arborvitaes are sometimes used for this purpose, requiring much the same kind of treatment as Irish Yews. When judiciously managed, these two associate well upon the same wall, and can be made to form a covering of about equal thickness. However, the Arborvitses have a very ferny-like appearance - that is, when they are nicely trimmed and well fastened against a wall. Their little fore-shoots or branches, of from 4 to 8 inches long, often remind one of the tip of the fronds of the Fern Filix-Mas, or the common Bracken (Pteris aquilina). These two, when well managed, have nothing of a coarse appearance, nor do they run long stretches, leaving some places naked, as many plants are liable to do.