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.
Dr. Hull writes thus in the Prairie Farmer: The finest effect we recollect ever to have seen, in growing a hedge of the arbor vitas, was one in which the plants were set two feet apart, and, after they had grown one year, the ground was then heavily mulched - say three inches deep - with old horse manure and saw-dust, in about equal parts, and small trenches were opened on each side, about twelve inches out, and all of the branches which were trailing on the ground, were bent and buried in the earth, with the ends turned up. Each branch so buried became rooted, forming, as it were, a separate tree. On such trees as had lost their trailing branches, those nearest the ground were bent down into the trenches, and held in place by wooden pins or forked sticks. A mulch like that under the trees was then spread one foot wide outside the rows of those buried branches, which kept the ground moist, and caused all to emit roots and become, as it were, separate trees. It would hardly be possible, by any amount of trimmiug.to make trees so thick or impervious as by this method, nor do we recollect to have seen so fine a pyramidal screen secured by any other means.