Rhododendron subsection Maddenia has long been cultivated at Logan Botanic Garden, an outpost of the Royal Botanic Garden, Edinburgh (RBGE). It is noted in RBGE’s Collection Policy as one of Logan’s representation themes. Half of RBGE’s Maddenia accessions grow there outdoors in the relatively mild climate that suits these tender plants. It was known that Logan’s collection did not represent the entire Subsection. Therefore, this study’s aim was to investigate how completion might be achieved. Existing literature and known specialists were consulted to compile a list of taxa, although this remains unresolved. Using RBGE’s BG-BASE data and an observational survey of Logan’s living collection, it is suggested that 24 taxa may be absent from the collection. Their native occurrence, ex-situ cultivation and IUCN Red List criteria were researched. Using this information, a simple value system was created in order to prioritise acquisitions that might best serve conservation. This article is abridged and revised from the author’s specialist project, completed in candidature for the HND Horticulture with Plantsmanship.