It is not fully hardy in temperate regions.
Most hybrid tea cultivars are not fully hardy in continental areas with very cold winters (below -25 C).
There are even one or two fully hardy species from Turkey.
If the particular rhododendrons were not fully hardy, flower buds may have been winterkilled.
Some varieties are not fully hardy in all areas.
It is fully hardy (at least in the British Isles).
This rhododendron from Korea is fully hardy and one of the first shrubs to bloom in early spring.
Given some shelter, this is considered one of the best evergreen shrubs with variegated foliage, though not fully hardy.
It likes full sun, is fully hardy and flowers in late spring and summer.
Not fully hardy, in frost-prone areas it requires some protection.