Rhododendrons are flowering plants that belong to a family of over 600 species, growing naturally almost everywhere in the world, from mountains in China to the state of West Virginia. They may be either evergreen or deciduous, and most have showy flower displays.
Rhododendrons include the plants known to gardeners as azalea. The mountain varieties have small petals and leaves, while the garden varieties have clusters of large trumpet-shaped blooms and glossy oval leaves.
Some species are invasive as introduced plants, spreading in woodland replacing the natural under story. It is difficult to eradicate, as its roots can make new shoots. Some species are poisonous to grazing animals. Some Rhododendrons have a toxin called grayanotoxin in their pollen and nectar. People have been known to become ill from eating honey made by bees feeding on rhododendron and azalea flowers. Honey resulting from this azalea has an hallucinogenic and laxative effect.
Most rhododendrons are now grown from tissue culture plantlets or from cuttings, usually rooted in August to October, in peat moss and sand or peat moss and perlite, under mist with bottom heat and with the use of root inducing hormones.
To root a rhododendron, peg a low branch into a trench, covering it with two to three inches of soil. Though this may require several months to finish, you can hasten the process by cutting a groove on the underside of the branch (the part that is buried, and facing the mother plant). This leaves part of the plant attached to the mother plant.
It is important first to realize that if you will be moving the rhododendrons that they are not very close to trees, as their roots may become intertwined. Such plants cannot be moved without destroying them. (See: Transplant Containers)
Deciduous azaleas may have sparse and widely spread out root systems. Care must be taken when moving them to get as many roots as possible, and if the root systems are small, the tops should be cut back drastically to within six to eight inches of the ground.
Smaller deciduous azaleas are usually more successfully moved than larger ones. Evergreen azaleas and large leaved rhododendrons have shallow fibrous root systems and should be dug with as large a root ball as possible. The root ball will likely not need to be too deep to get most of the roots, but it should be wide.
It is best to plant newly dug rhododendrons right away, but if you are not able to do so, the plants can be heeled in with mulch, such as pine bark soil conditioner, or even potted up in very large containers using good potting medium such as the pine bark soil conditioner. In cold climates they should be planted before winter to keep the roots from dying from extremely cold temperatures. Plants can be held this way until you are ready to place them in their new location.