A new and distinct cultivar of Hydrangea macrophylla (Thunb.) named ‘BC8.3’ originated as a controlled cross between varieties. The cultivar ‘BC8.3’ can be blue or red depending on the acidity of the soil and the presence of aluminum. The variety ‘BC8.3’ has compact, attractive inflorescences with large sepalous florets that do not completely hide the non-sepalous florets at the center of the cyme, attractive sepal pigmentation, and stems that branch easily and are relatively strong. When grown without aluminum, the upper sides of the sepals of the sepalous florets are primarily R.H.S. 73 A (red-purple group) at the center of the floret and the sepals are R.H.S. 56 A (red group) at their periphery.
