Answer: Your Hydrangea macrophylla is borderline in your gardening zone, so cross your fingers! Nikko Blue is a vigorous plant and the roots are hardy to -20F. However, since the plant will bloom on shoots produced on the previous year's growth, if the top freezes down in the winter, it won't bloom the following year. You can mulch with any organic matter, but stay away from plastic or anything else that will trap moisture. Use leaves, pine boughs, or straw as a protective mulch over the crown of the plant and as high up on the stems as you can. Cut back any winter damaged stems in the very early spring, making sure you leave 2-3 leaf scars or buds on the remaining stems. New shoots will be produced from these leaf scars, which should produce flowers in the summertime.
Hydrangea's like a slightly acidic soil so mulch over the root area with peat moss and feed monthly during the growing season with an acid-based fertilizer.
Hope your Nikko Blue blooms with great gusto next summer!
Q&A Library Searching Tips