Best time is early spring before any shoots start to form. Dig around the plant as far out as the width of the top of the plant. Shake off loose dirt, trying not to disturb small roots. Dig the new hole same size as the root ball you just dug up. Before planting, add 2 tablespoons of Epsom salts and mix into soil in the bottom of the new hole. Add water into the new hole and then place the plant into the hole so that the plant is at the same depth as the previous spot. Water well. In 7 to 14 days, apply a fertilizer made for hydrangeas.