Evergreens should not be transplanted to a "cold" soil, but rather into a soil that is sufficiently warm to permit root growth to begin immediately and to continue either during the spring and summer or during a period of two or three weeks in the fall before the plants become dormant. The best season for transplanting evergreens, especially in colder climates, is during the spring months, just as new growth is beginning. This is done for the purpose of giving the plants an opportunity to go through one growing season and thereby better to establish themselves to withstand cold weather in their new location. Stable manure which is not thoroughly rotted should never be placed in contact with or close to the roots of any evergreen plants. Fresh stable manure mixed in any soil where evergreens are to be planted is fatal to the plants.
When evergreens are shipped from a colder and more backward section to a more advanced growing season in a warmer section of the country it is usually advisable to transplant in the fall. Evergreens in the opposite-leaved group, comprising the arborvitęs, retinosporas, and junipers, should seldom be transplanted in the fall after the plants begin to shed their leaves. This condition may be recognized when a considerable portion of the leaves throughout the plant turn brown.
If it is necessary to transplant evergreens during the fall when the growing season is completed and the ground is subject to light freezing and thawing, the best treatment is to immediately place around each newly transplanted plant a light mulch of stable litter three or four inches in depth. This is done in order to maintain the ground at an even temperature and to keep the soil sufficiently warm so that some root growth will start before freezing conditions develop.
It is the general practice, in shipping evergreens, to "ball-and-burlap" them. In this condition evergreens can be shipped for a considerable distance, and if properly wet before being shipped they will remain normal for a period of two or three weeks. As a rule, evergreens for transplanting are grown in a soil which is composed of some clay rather than in a soil which will not hold together around the roots.
In the northern sections of the United States it is generally assumed that spring planting of rhododendrons is more desirable than fall planting. This is recommended mostly because plants transplanted in the spring have a better opportunity to establish themselves and are less liable to injury during their first winter. If rhododendrons are to be transplanted in the fall, it should be ascertained whether the locality from which the plants are coming has received a normal amount of rainfall prior to the time that the plants are dug. The greatest difficulty in transplanting rhododendrons is that with insufficient rainfall and a dry season, before the plants are dug, there is insufficient moisture stored in the plants to offset the transpiration caused during the winter months. When material is transplanted in the late fall roots do not seem to make sufficient growth to take up the necessary moisture from the soil, and therefore the plant must carry itself through the winter on the strength of the moisture stored up in the cells. This appears to be the main cause for criticism against the fall planting of rhododendrons. It should be borne in mind that the roots of rhododendrons and of the kindred plants such as the azaleas, feed near the surface of the ground. For this reason.and also because of the evergreen foliage characteristics some root action should be encouraged, if possible, during the milder winter months, and thus mulching of such plants is vital. Extreme care should be exercised in transplanting these types of plants. Plants should be put in a heavy, well-rotted leaf mold soil at no greater depth than the plant stood before moving from its previous location. It is a common practice in the preparation of lawn areas and planting areas, especially in sections where clay soil predominates, to apply a large amount of lime. Because lime in the soil is an element very injurious to the growth of broad-leaved evergreens, none should ever be put in or close to any beds which are to be planted with rhododendrons. This is also true of building plaster and mortar, which is frequently thrown into the soil adjacent to the foundation of buildings where these plants may later be put.
Rhododendrons should never be planted in a location where the soil around the roots will dry out. They should be sheltered from the morning sun and also from extreme exposures of wind. During most of the growing season the falling of the dew as a result of the condensation of the moisture in the atmosphere causes little globules of water to remain on the surface of the leaves during the night. These particles of moisture are slowly evaporated during the early part of the morning. The rays of the early morning sun coming in direct contact with the leaves of rhododendrons on which these particles of moisture are still present are concentrated and focused by these many little "lenses" and cause a burning of the surface of the leaves which in the case of rhododendrons is extremely injurious to the plant. This is one of the most important reasons why rhododendrons with their sensitive leaf surface should not be exposed to the direct rays of the early morning sun, at least until after the heat of the day has caused an evaporation of the particles of moisture remaining on the leaves from the previous night. The baking out of the soil around the roots is extremely injurious to them. If this soil can be maintained at an even, cool temperature, their normal growth is better assured during the summer. They are not so much injured because of the cold, but because of the intense sun which causes evaporation of moisture from the leaves at a time when the ground is frozen and at a time when the plants are unable to replace this loss of moisture by additional water taken through the roots from the soil. This condition is especially true in the clay loam soils of the middle west.
They should never be watered with any water which contains lime. This is equally as important as the necessity of not planting rhododendrons in a limestone soil. It matters not how much the soil may be changed in the beds or how much leaf mold may be put in the beds in which to plant rhododendrons if the water with which they are frequently soaked comes from a limestone region.
Rhododendrons will grow in any good garden soil, but they much prefer a soil with a good deal of humus in it, and they should be thoroughly mulched with leaf mold soil which should never be cultivated, but left in its native woodland condition.