Bigleaf, oak-leaf and panicle hydrangeas are well-suited to container culture, and growing them in containers has some advantages. You can move container-grown hydrangeas out of sight after the leaves drop and the shrub is no longer interesting. Hydrangeas fail to bloom when hit by freezing temperatures before they are completely dormant and when snow and ice damage the branches. You can move container-grown plants to a protected area when unseasonable or severe weather threatens. Gardeners enjoy manipulating the colour of bigleaf hydrangea blossoms, and the soil manipulations are easier to accomplish with container-grown plants.
Big leaf hydrangea (H. macrophylla) is also called Japanese, French or snowball hydrangea. The two flower types produce remarkably different effects. Mopheads are big balls of showy flowers, and lacecaps are large central discs of tiny fertile flowers with large, showy, sterile flowers around the outer edges. The flowers are naturally white, but you can change the colour to pink or blue by adjusting the soil pH and aluminium content. Variegata is a lacecap type with showy, variegated leaves. Tovelit is a dwarf shrub with mophead flower clusters. The new foliage on Golden Sunlight starts yellow, maturing to pale green. The lacecap flowers start light green and mature to pale pink.
Panicle hydrangea (H. paniculata) produces long panicles of flowers from midsummer until fall. The branches often droop from the weight of the 6- to 8-inch panicles loaded with masses of white flowers. The Swan and Limelight cultivars are well-suited to containers, with panicles that grow up to a foot long. They make showy specimen plants for decks and patios when trained to the shape of a small tree. Little Lamb and Pee Wee are dwarf varieties with a compact habit.
The ornamental qualities of oak-leaf hydrangea (H. quercifolia) make it ideal for patio containers. The flower panicles measure up to 14 inches and the foliage has outstanding fall colour in shades of burgundy to purple. The cinnamon-coloured, exfoliating bark keeps the container interesting after the leaves drop. The Flemygea cultivar has large, showy panicles on erect stems. Pee Wee, Little Honey and Sike's dwarf are small cultivars that work well in containers.
A dwarf hydrangea that grows only to 2 feet tall grows well in a 12-inch diameter container. Larger shrubs need an 18-inch pot. Use a good quality soilless potting mixture with particles no more than 1/4 inch wide. Most potting mixtures contain enough plant food to sustain the plant for a month or two. When the fertiliser is depleted, use a slow-release fertiliser according to the package instructions. Keep the soil moist to the touch, but not soggy or wet. Water-absorbent crystals or gels can help maintain the moisture level. Place the containers in a lightly-shaded location, with bright sun in the morning and a little shade in the heat of the afternoon.