It would be nice if your Rhododendrons were only to die from old age. Rhododendrons are generally long lived shrubs that would then outlive most of us and this article wouldn’t be needed.
However the natural world is not like that and accidents do happen. Gardener inflicted death can be caused by being over protective or trying too hard.

What Makes a Rhododendron Die

1. Rhododendrons are fibrous, shallow rooted plants that need good drainage to perform well and excess water is currently the major cause of death. Digging a big planting hole that creates a water sump is the way to drown your Rhododendrons.
2. Rhododendrons do not have taproots to take a drink, unlike trees. Therefore Rhododendrons need frequent watering particularly when young or if spring is very dry.
3. Another cause of rhododendron death is the excessive application of fertilizer directly at the base of the trunk of the plant. A good rule of thumb is to fertilize more frequently at lower concentrations rather than one large dose especially for small plants or newly transplanted plants.
4. A fourth reason for rhododendron death is planting too deep. As indicated earlier, rhododendrons are shallow rooted plants and if buried they will stagnate or even die.
5. Another reason that rhododendrons die is from cold winter temperatures with deep frozen soils. Most rhododendron can be grown in cold areas but I mulch around tender species.
6. Not many varieties can survive unprotected all-day sun and some say they ‘are doomed’. In general rhododendrons in extreme climates benefit from filtered light and partial shade but there are some varieties that can stand direct sun.
7. Sudden oak death fungus Phytophthora ramorum has recently infected Rhododendron ponticum and some container grown plants so this problem is moving up the chart of the causes of dieing.
8. Fungus that causes ‘die back’ thrives in the same general conditions preferred by most rhododendrons. I am sometimes tempted to use a fungicide.
9. Physical damage by rabbits, Deer or football playing grand children may cause breakages but should not lead to death.

None Fatal Rhododendron Problems

Rhododendrons are a hardy species – they need to be coming as most do from the Himalayas
Frost has got to these rhododendron flowers but that is not cold enough to kill the plant.
Dried black buds may be caused by insect damage or water shortage.
Burned tips on this year’s new growth is typically indicative of lack of water as the plant withdraws water from the tips of the new foliage first.