2018 ASHS Annual Conference

Hydrangeas (Hydrangea macrophylla) contain an anthocyanin pigment within the sepal that naturally produces a pink or red color. In the presence of aluminum (Al) the pigment will bind with the Al producing a blue or purple color. While most hydrangeas are marketed as a pink or blue there are some red cultivars. Red cultivars are managed similar to pink varieties in order to express their true red coloring. The purpose of this study was to determine if applications aluminum sulfate (Al₂(SO₄)₃) would change the color of the true red sepal. We treated ‘Hot Red’ hydrangeas with 0, 1.2, 1.8, 2.4, and 3.0 g/L of Al₂(SO₄)₃ applied during weekly irrigations. We measured the Al levels in the sepals, leaf tissue, and substrate leachate by ICP analysis at full bloom. Sepal colors were evaluated by visual analysis and measured using a handheld colorimeter. There was a positive correlation between the concentration of Al₂(SO₄)₃ applied and the level of Al in the sepal, leaf tissue, and substrate leachate. Regression models illustrated that each tissue continued to accumulate higher concentrations of Al as the Al₂(SO₄)₃ concentration increased. There was a noticeable change in sepal color with increasing concentrations of Al₂(SO₄)₃. Color data indicated that higher Al₂(SO₄)₃ concentrations resulted in darker sepals with more blue and less red coloration. Based on the findings, growers producing ‘Hot Red’ hydrangeas have the ability to manipulate the sepal coloration by applying Al₂(SO₄)₃.