A new and distinct cultivar of Hydrangea macrophylla (Thunb.) named ‘BC7.8’ originated as a controlled cross between U.S. Pat. No. 18,592, named ‘True Blue’ and the commercial variety ‘LK49’. The cultivar ‘BC7.8’ can be blue or red depending on the acidity of the soil and the presence of aluminum. The variety ‘BC7.8’ has relatively large, attractive inflorescences with relatively large sepalous florets, distinct sepal pigmentation and good commercial characteristics. When grown without aluminum and under soil conditions to create pink flowers, the upper sides of the sepals are R.H.S. 70 C (red-purple group) and the under sides of the sepals are R.H.S. 65 C (red-purple group).
