Rhododendron Species for Changing Climate
Rosina T. Schmidt
The summer of the year 2021 on Vancouver Island was perfect for swimming in the Ocean: sunshine day in day out and temperature above normal. Alas, there was no rain to water our Rhododendrons between middle of June and all the way to 10th of September. Our gardens in the city of Nanaimo were on water restrictions and most of the wells in the surrounding areas did not fare much better. It makes us wonder, which genus Rhododendron are more heat tolerant and need less water once established?
Our gardening colleagues Dorothee Kieser of NRS and Martin Wilkie of Christchurch, Australia are sharing with us their recent experiences.
Martin Wilkie’s research of rhododendron species that faired better down-under under harsh and hot condition names the following plants:
R. yakushimanum family: R. pachysanthum and R. koichiro Wada – they are hardy, free flowering, tolerant to sun and light shade.
R. maddenii ssp. crissum, is one of the most heat and drought-tolerant plants in the maddennii subsection.
R. catawbiense, proven to be invaluable for its extreme hardiness.
R. smirnowii, dense pale-brown indumentum under the leaves is a good deterrent of thrips. Extremely hardy.
R. caucasicum, grows well in relatively poor, dry soil, low in organic matter.
R. insigne, of subsection argyrophylla, a dense bushy shrub in full sun, leaves are noticeable thick and rigid, dark shiny green above with a pale plastered shiny indumentum.
R. arboretum heat and drought resistant, with thick leathery leaves that have indumentum on the lover leaf surface.
R. arboretum ssp. nilagericum, its glossy, bullate, convex leaves have persisted in the characteristics in two outstanding hybrids (Rubicon and Nilgris). It is an excellent plant for hot and dry climates.
R. decorum, R. decorum ssp. decorum, and R. decorum ssp. diaprepes are the most plentiful species in the wild of Sichuan, Yunnan and N. Burma. Often found in very dry sites where most other rhododendrons cannot survive.
 See October 2021 NRS Newsletter