The most important question is: What size Rhododendron do you want? Dwarf Rhodos and Evergreen Azaleas tend to be slow growing (5-10cm/ year) and reach up to
1m in height, perfect for boarders or as a potted plant. Because of the slow growth rate, it might be a good idea to buy a plant close to the size you want.
Tall hybrid Rhodos and Deciduous Azalea will grow up to 2m, at a rate of up to 50cm a year, but can spread to more than twice that width making them perfect for hedging or screening. Nearly all rhodos respond well to pruning so as long as you are not afraid of a bit of landscaping, you can keep even the large growing varieties at a manageable size.
Evergreens are popular because they offer all year structure but deciduous Rhododendrons offer a fantastic autumn display of fiery colours and grow quicker, to a larger size.
All rhododendrons prefer at least partial shade, either for part of the day or filtered through the branches of a neighbouring tree. This helps ensure the setting of buds and so a good flowering but you can find some sun tolerant varieties.
The tall hybrid Rhododendrons have the largest flowers and the longest flowering period, sometimes from February through to July. Azaleas have smaller flowers, but the smaller and more intricate petal arrangements create quite the spectacle.