The varieties grown for indoors are the mop-headed hydrangeas from Japan, as these tolerate being under cover. To grow well, they need cool, light, and airy conditions; they are well-suited to growing in a cool conservatory. They form short, woody shrubs bearing large, oval leaves.
The flowers are green in bud, opening blue, red, pink, or white in a rounded cluster. The blues need to be kept in an acid soil mix or they change color to pink or red. They are ideal for use in a large container, because they will flower year after year. Once they have outgrown their allotted space, they can be planted outdoors.
Size: Height 2 ft. (60 cm).
Light: Indirect sunlight.
Temperature: Cool; preferably below 60°F (15°C).
Moisture: Keep thoroughly moist from spring to fall.
Feeding: Provide standard liquid fertilizer every two weeks.
Propagation: Only really viable on a plant for outdoors. Take 4 in. (10 cm) tip cuttings in spring or summer.
Special needs: After flowering, either discard the hydrangea or plant it outside, as it is unlikely to bloom indoors a second time.