With varieties that flower in vibrant blues, reds and various lighter shades, hydrangeas are a wonderful addition to any landscape. Many species bloom in summer, which provides a nice balance of color to the garden when spring has passed. Although hydrangea is generally considered to be a shrub, a few species can be grown as small trees.
Hydrangea paniculata grandiflora, commonly called peegee hydrangea, is probably the most popular cultivar that can be grown as a tree. When pruned correctly, the peegee can reach 20 feet in height and produces huge ivory blooms in late summer that fade to pink and brown through the fall. The oakleaf and nikko blue hydrangea varieties also make nice ornamental trees, although much smaller in size than the peegee.
Hydrangeas thrive in acidic soils, preferably in the range of 5.0 to 5.5. A soil test followed by the appropriate amendment is the first step in treating plants that are in poor health or failing to bloom. When planting, a well-drained location that receives morning sun and afternoon shade will best suit these hydrangeas. Although most plants are quite cold-tolerant, the peegee variety is especially tough, with a zone 3 hardiness rating.
Pruning is one of the more challenging aspects of hydrangea care, as there are no general rules that apply to all varieties. Fortunately, the peegee hydrangea requires little regular pruning but does need some shaping to establish it as a tree. Basal branches and suckers must be removed to maintain the single stem. The branches that fan out to form the tree body should also be pruned back to no more than three or four leaf nodes, unless drooping is desired. Tree hydrangeas should be pruned in early spring before the start of new growth.
Hydrangeas can be propagated easily by taking cuttings. Stem tips should be cut below the second leaf node and planted in a sandy medium out of direct sunlight. In the absence of a greenhouse, a small planting tray with cuttings can be placed in a sealed, clear plastic bag to preserve moisture and warmth. Hydrangea seeds may also be collected in the fall and sown in the spring. The seeds need to be stratified before planting, so it best to keep them in a cool environment, such as a refrigerator, for several months.
Hydrangea Tree Care
Hydrangea trees need little fertilizer, but a balanced blend may be applied in early spring if desired. Mulching is a better way to add nutrients to the soil, so keep several inches of leaves, bark or wood chips around the tree out as far as the drip line. Be sure not to let the mulch touch the trunk to avoid potential rot problems. Like all hydrangeas, the paniculata grandiflora variety likes moist but not wet soil.