The Osmocote Plus Outdoor/Indoor  plant food is great for all hydrangeas and should be used in the spring. The Endless Summer hydrangeas are hardy to -30 degrees so in your zone just cover the plants with a mulch of straw, bark or pine needles after the leaves fall. Remove this protective winter mulch in spring and apply the fertilizer to the bare soil at the base of the plant. Do not prune in the late summer or fall. These hydrangeas bloom best if you don't prune them at all so give your hydrangea plenty of room. Keep growing, Marianne Binetti