Hydrangeas are deciduous shrubs belonging to the Hydrangeaceae family. Hydrangea plants are typically winter hardy in USDA zones 3 to 8, and display flowers from July through September. These plants thrive in rich, moist soils in partially shady to fully sunny locations. Various panicle hydrangea (hydrangea paniculata) varieties can be easily pruned into a tree form.
The Grandiflora is one of the most cold-hardy hydrangea varieties. This upright plant typically reaches heights between 10 and 25 feet with spreads ranging from 8 to 16 feet. The Grandiflora hydrangea blooms conical clusters of white flowers that turn pink with maturity. The flower clusters reach up to 1 1/2 feet in length. The branches often arch down under the weight of the flowers, so gardeners wanting a tree form should stake this plant. This hydrangea variety sometimes contracts bud blight, leaf spot and powdery mildew. Nematodes and aphids occasionally attack these plants.
The Little Lamb hydrangea is a compact panicle variety that reaches up to 8 feet tall with slightly smaller spreads. This hydrangea plant displays white flowers in the summer and fall. This variety earned its name because each flower panicle looks similar to a small lamb. The green leaves obtain a purple or yellow tint in the autumn months. Bacterial wilt, rust, mites and scale are all occasional problems. This compact hydrangea variety works well as a small tree tree in borders.
The DVP Pinky hydrangea cultivar is an upright variety easily pruned into tree form. This cultivar matures between 6 and 8 feet in height with slightly smaller spreads. Dark oval leaves turn yellow or purple tones in the autumn months. Conical flower clusters bloom white but turn dark pink with age. This cold-hardy hydrangea also tolerates urban conditions. Bud blight and rusts often attack these plants. Tree-form versions work well as lawn specimens and borders.
Interhydia hydrangeas are fast-growing varieties that quickly reach 8 to 15 feet in height with similar spreads. This panicle hydrangea blooms conical clusters of flowers that emerge with white petals, but mature to pink. The Interhydia hydrangea makes a great tree-form plant because it has stiff stems that won't droop under the weight of the flowers. Green leaves turn purple or yellow in the autumn. Interhydia hydrangeas are somewhat vulnerable to leaf spot diseases, powdery mildew, mites and scale. This variety works well in woodland gardens and borders.
The Limelight panicle hydrangea reaches between 6 and 8 feet tall with similar spreads. The flowers emerge white, but then turn lime green, then pink and then fade to beige. This winter hardy variety also tolerates humidity, high temperatures and urban environments. The green leaves turn red in the fall. Mildew, bacterial wilt, mites and aphids are occasionally problems. Tree-form Limelight hydrangeas work well as borders and accents.
Tardiva hydrangeas mature to heights ranging from 8 to 12 feet and widths between 7 and 10 feet. While the Tardiva can be pruned into tree form, it typically flowers best as a large shrub. This winter hardy plant bears green leaves that turn purple in the autumn. The white flowers become pink to purple shades with age. Tardiva hydrangeas are susceptible to leaf spot, powdery mildew and nematodes. This variety works well as borders and accents.