You should care for a potted hydrangea just as you would any houseplant. Keep the root zone moist; not wet, not extremely dry. Fertilize once a week by watering with a water-soluble fertilizer according to label instructions. Another option is to use slow-release fertilizer granules, which are generally applied every several months. Place the plant where it will receive bright light, but not close enough to window glass to heat-scorch leaves. If you put it outdoors, find an area that receives morning sun and afternoon shade.
Fertilizing about once per month with aluminum sulfate will help to keep blue flowers.
