I have been growing Rhododendrons for over 30 years and these, for me, are the fundamentals.
The soil must be acid. Marginally acid soil can be made more acid by adding sulphur to the soil. Ericaceous compost can be added to stiff clay soil, enabling the fine roots to feed on the clay more easily.
The removal of dead flower heads improves plant appearance and directs energy into the new growth. The ground must not be too dry or water-logged. A test for the latter is to pour water into the proposed planting hole. If it fails to drain in 20 minutes, choose another location.
Ideally choose more sheltered sites in dappled shade, but avoid deep shade under trees. Rhododendrons grow best in areas of higher rainfall. They are more difficult to grow in drier parts of the country.
In dry periods avoid watering with tap water if you can, as it contains calcium which reduces acidity around the roots, particularly in hard water areas. If there is no rain water alternative, then do not use tap water for more than a month or two.
I usually plant Rhodos in groups, spacing the plants according to their 10-year height and width. e.g. tall Rhodo varieties 1.8m spacing. Medium 1.4m. Low 1m. Azaleas 1.2m. Provision of a mulch, bark, leaf mould, pine needles etc. in a new bed helps to trap light rain, deters weed growth and the humous feeds the plants.
When planting Rhodos I firm them by hand because compacted soil does not suit them.They quite like being moved and almost say 'thank you' for the help loosening and aerating the soil gives to their roots.
Most varieties are hardy enough to grow in the UK. Their roots develop sideways and seldom exceed 25cm in depth, which simplifies planting and moving.
Flowering times vary, making them adaptable for different locations and sequential flowering over up to 6 months. Leaves also vary widely in size, shape and colour. About 40% of deciduous azaleas are scented; while a few pink and white Rhodos also have scent.