Control of Sepal Color and Growth of ‘Pink Ari’, ‘Morning Star’, and ‘Green Ari’ Hydrangeas by Aluminum Sulfate Treatment

Abstract

Background and objective: This study was conducted to examine the change in sepal color and growth by treatment with aluminum sulfate of three Korean hydrangea cultivars, 'Pink Ari', 'Morning Star', and 'Green Ari'. Methods: The rooted cuttings of three hydrangea cultivars were planted in pots with 300 g of horticultural medium mixed with 0, 3, 9, and 15 g of aluminum sulfate (AS). The shoot growth was measured by plant height, leaf length and width, stem diameter, chlorophyll content, and mortality rate, and flowering characteristics were measured by the number, width, and height of inflorescences and the color of sepals.Results: For the hydrangeas 'Pink Ari', 'Morning Star' and 'Green Ari', it was found that as the amount of aluminum sulfate mixed for the treatment was increased, the pH of the media reduced and became more acidic. Moreover, the higher the amount of AS mixed in, the shorter the plant height was, the more the growth of shoots was suppressed, and the higher the mortality rate. In addition, the number and size of inflorescences under treatment with 9 and 15 g of AS decreased more than those under treatment with 3 g. The sepal color showed a different reaction depending on the cultivars. The 'Pink Ari', which has deep pink sepals, remained deep pink when treated with 3 g of AS, but changed to light pink when treated with 9 g or more. On the other hand, the 'Morning Star' and 'Green Ari', which have pink sepals, changed to blue and light blue, respectively, when treated with 9 g or more of AS.Conclusion: When treated with more than 9 g of AS, the plant height of 'Pink Ari' was shortened and its marketability was greatly reduced, and it was judged that it would be appropriate to grow it as a potted hydrangea with light pink sepals when treated with 3 g of AS. The sepal color of 'Morning Star' changed to blue when treated with 9 g of AS, but it was found to be unsuitable for cultivation for potting due to the short plant height and small number of inflorescences. Treatment with 9 g of AS changed the sepal color of 'Green Ari' to light blue and light green, and it had plant height and number of inflorescences suitable for pot cultivation.