This section is from the book "Beautiful Gardens - How To Make Them And Maintain Them", by Walter P. Wright. Also available from Amazon: Beautiful Gardens: How To Make And Maintain Them.
We use the term "planting" when plants or shrubs are first put into the garden, and the word "shifting" when an established plant is moved from one place to another. The great majority of trees, shrubs, and plants may be put in between the end of October and the end of March. The case as between autumn and spring planting may be briefly stated as follows: In autumn the nursery quarters are full, and there is no difficulty is securing good plants of any varieties in the catalogue; in spring the nursery is depleted, and the best plants of the best varieties have been sold - the early bird has got the worm. In autumn the soil retains some of its summer warmth, and the plants make a few fibres before the winter. In spring, if the winter has been wet, or has brought much snow, the soil is cold. In autumn garden work is decreasing, and there is ample time for planting; in spring work is increasing, and there is less time. The balance appears - indeed, is - on the side of autumn planting, but it is only fair to point out that the autumn planter has to face the risks of winter; the spring purchaser leaves those dangers to the nurseryman!
Equally as important as the period of planting is the state of the soil. It should neither be quite dry nor sodden. Contrary to general opinion, a very wet soil is as bad as a very dry one. The author has a lively recollection of the planting of several hundred pounds worth of shrubs and trees by a well-known nurseryman on a light, gravelly soil, which dried badly in summer. The nurseryman decided to "puddle" them in order to give them a start. They were practically planted in mud, and they nearly all died.
If the ground is very wet or frostbound when shrubs arrive lay them nearly flat, with their roots in a shallow trench. With soil over the roots, and litter over the branches in very hard weather, they will lie safely for months, if necessary. The operation is called heeling-in. The planter should work by the following rules, and he will then have few failures:
(1) To plant when the soil is moist.
(2) To make relatively large holes, and spread the roots well.
(3) To avoid planting deeply.
(4) To make the soil firm over and around the roots.
(5) To stake securely.
These rules will equally apply to shifting. If it has to be done when the plants are growing, and the soil is dry, the operator should chop round them with a spade a few days before they are taken up, and when the time for shifting arrives, give a good soaking of water a few hours before taking them up. Many shrubs, including Rhododendrons, shift best in spring - say the early part of April. When a shrub has to be transplanted some distance the roots should be wrapped in a mat.