A hydrangea tree, also known as Hydrangea paniculata or panicle hydrangea, is a large shrub that is often pruned to look like a multi-stemmed tree. A hydrangea tree grows up to 25 feet in height and 20 feet in spread. The showy, white blooms fade to a purplish-pink color by late summer, while the dark-green foliage turns a pale-yellow color. The upright branches tend to collapse under the weight of the blooms in fall. They need to be removed to keep the tree from looking shaggy.
Choose a sunny or partially shaded site on well-drained, moist or loamy soil to grow a hydrangea tree. Hydrangea also tolerates clay, sand, acidic and alkaline soils.
Plant the hydrangea tree in fall to ensure the roots develop before spring bloom. Dig a planting hole that is twice the depth and width of the root ball. Tease out any coiled or restricted roots. Place the root ball in the hole, and then backfill the hole with soil to a level that is two-thirds to the top of the root ball. Tamp the soil around the hydrangea so it’s firm. Fill the hole with water and allow it to drain. Finish filling the hole with soil until the root ball is covered.
Spread 2 inches of mulch around the base of the hydrangea tree, keeping a 3-inch gap between the mulch and the trunk to avoid crown rot and insect damage. The mulch conserves water loss and keeps the root system cool.
Provide the hydrangea tree with 1 inch of water per week, adjusting for rainfall. Hydrangeas needs consistent moisture, but do not to overwater your plant. Hydrangea develops root rot in soggy and poorly drained soils or after lengthy periods of rainfall.
Apply an all-purpose fertilizer, such as 12-4-8, 16-4-8 or 10-10-10. Spread the fertilizer at a rate of 1 pound per 100 feet, divided over two applications in April and June. Water helps dissolve the fertilizer.
Look for powdery mildew and Cercospora leaf spot diseases. Powdery mildew appears on the lower surface of leaves as small, round and white patches. Cercospora leaf spot presents as brown or purple spots on leaves at the base of the tree. Remove diseased and fallen hydrangea leaves to avoid disease spread.
Prune a hydrangea tree in spring to a single-stemmed tree form, or allow it to grow as a shrub and remove the lower branches to make it grow as a multi-stemmed tree. Cut the branches back to within 1 to 3 feet to keep the tree small. Remove all but three to five main branches to give the crown the desired shape. Remove weak, dead or diseased branches.
Propagate hydrangea trees through layering in early to mid-summer. Bend a healthy branch down to the ground, then scoop out a trench below the branch. Hold the end of the branch down with a peg-type clothespin or a brick. Mound the soil over the branch, allowing at least 6 inches of the branch to remain uncovered. Gently firm the soil and keep it moist until new growth forms. Cut the newly rooted hydrangea plant from the main tree and transplant immediately.