Blue hydrangea, known for its showy periwinkle blooms brought on by acidic soil, grows beautifully in a pot during the summer. You must give it frost protection or bring it inside during the winter, and then repot your hydrangea in the spring to give it breathing room for the new season.
Water your plant while still in its original pot. Let the water drain for 10 or 15 minutes.
Fill the new pot with potting soil specifically made for acid-loving plants. The-Artistic-Garden.com says you can make your own potting soil by mixing two parts packaged potting soil, two parts coarse sand, two parts peat moss, one part leaf mold and 1/3 part well-composted manure.
Pull gently on your hydrangea to loosen it from the original pot. Gently brush off excess dirt, tug lightly on any wrapped roots, and then place in the new pot. Backfill with potting soil, tamp down firmly and water.
Water daily for the first week, and after that when the soil is just barely dry. Potted hydrangeas dry out very quickly and require large amounts of water. Fertilize every two weeks during the growing season with a liquid fertilizer for acid-loving plants or one that promotes blooming. If you want to keep the flowers' vibrant blue color, do not use fertilizer that contains phosphorous.
Place your pot in bright, but not direct, sunlight.