One of our older plant encyclopedias says that there are 4,000 species of Rhododendron. More recent books indicate the number closer to 500-900, another saying 800. Anyway there are many hybrids.
It seems like azaleas are smaller, daintier rhododendrons, but that is a misconception because there are very tall azaleas and very small, ground-hugging rhododendrons. A few of our plant books say that the rhododendron has ten stamen and azaleas have only five. Others say the distinction is purely artificial.
There are many books and web sites on azaleas and rhododendrons, so here we are only giving you the basics.
There are deciduous and evergreen azaleas divided into subgenera Pentathera and Tsutsusi and originated in many habitats around the world from forests to alpine and from sea level to high altitudes.
Even though azaleas come from a variety of conditions, they share the same general cultivation needs. Their roots lack fine feeding hairs at the tips. Instead, the entire root ball is a mass of fine roots and there is no tap root which make azaleas ideal for container cultivation and easy to transplant. However fine roots dry out quickly in dry conditions and rot if waterlogged. They do not penetrate poor soil conditions very well - I have seen them planted in clay and if the hole is large enough they will grow as if in a container, but they will never expand into the clay.
Azaleas need loose, open, well-aerated, acidic soil with plenty of humus to retain moisture. They need regular mulching that enables their shallow roots to spread and develop. In wet areas or alkaline soil plant in raised beds.
Most azaleas are woodland plants that prefer light shade or at least protection from the hottest sun and strong winds.
Azaleas are at their best planted in groups under pine trees (for the acidic soil).
Pruning azaleas is not necessary. Just remove unwanted or damaged branches after flowering.
There are many successful ways of propagating azaleas. Softwood cuttings from late spring to midsummer; semi-ripe cuttings from midsummer to autumn; layering in spring and autumn; grafting in winter; and seeds in winter and early spring.
In her book, "Wicked Plants," Amy Stewart warns, "Eating any part of the plant can cause heart problems, vomiting, dizziness, and extreme weakness."