This section is from "The Horticulturist, And Journal Of Rural Art And Rural Taste", by P. Barry, A. J. Downing, J. Jay Smith, Peter B. Mead, F. W. Woodward, Henry T. Williams. Also available from Amazon: Horticulturist and Journal of Rural Art and Rural Taste.
I am often asked the question: Can evergreens be trimmed, and if so, when is the best time ? After quite a number of years' experience, I have found the best time for trimming pines is after they have made most of their growth, that is, the White Pine, Austrian, Scotch and Corsican.
Evergreens grow in the first part of the season, and after they are nearly done growing, before the wood becomes hard, pinch the new wood off with the thumb and finger, or cut it with a knife. This, I think, is the best way to trim pines.
For Norway, Spruce, Balsam and Fir it is best to trim early in the season, before they commence growing, say from the first of March to the last of April. The Balsam does not require much trimming, unless it is cut off the side limbs, so as to keep the tree in good shape. If the top is cut off, the growth will be retarded very much, in some cases for two years or more. But this is not the case with the Norway and Spruce, if the top is cut off, it will make a vigorous growth in the same season. As the wood is hard, it is best to use a sharp knife. Hold the knife so as to cut from the underside, then it will not show.
Persons wishing their trees trimmed will find this way very good, and resulting from experience. A very little time spent will keep any tree in good shape. - Cor. Medina, 0., Gazette.