Evaluating High Soil pH Tolerance of Rhododendron Cultivars

Abstract

Rhododendrons (Rhododendron ssp.) are among the most popular flowering shrubs grown in landscapes in the temperate zone. Despite this popularity, rhododendrons do not tolerate soils with a pH of greater than 6.5 because in such soils they are unable to obtain iron for use in chlorophyll production. This makes rhododendrons especially difficult to grow in the neutral to high pH soils of the Midwest. My experiment tested recently released, reportedly elevated pH tolerant German rhododendron cultivars in the ‘Inkarho’ series for high pH tolerance. Preliminary assays of leaf chlorophyll levels and overall growth in elevated as compared to low pH soils support the hypothesis that the ‘Inkarho’ cultivars are resistant to elevated pH soils. These results could help researchers at the University of Minnesota in their efforts to breed rhododendrons that are better adapted to the high pH soils of the Midwest.