The Boursault Catawba Rhododendron is an old, hardy variety. Possibly not as hardy as the ironclads, it is nevertheless recommended in, for example, the Northeast USA. According to Hachmann of Germany, it can withstand temperatures of -30oC. The Boursault Catawba Rhododendron is a choice of several R. catawbiense hybrids prior to 1849, but the precise genome is not known.
The dark purple buds break into light mauve flowers in around mid-June. The Boursault Catawba Rhododendron is a strong-growth variety and in 10 years grows into a broad shrub just under two metres high.
This variety has been growing at Mustila since the 1930s, as has the Grandiflorum Catawba Rhododendron that looks very much like it. Both reach a height of only about one metre at Mustila. The reason lies not necessarily in the low temperatures alone, but in the fact that the heavy snow presses the limp branches against the ground in winter.