Growing Tree Hydrangeas (Panicle Hydrangeas)
Characteristics and Cultivation
Tree hydrangeas, also known as panicle hydrangeas (Hydrangea paniculata), are fast-growing flowering shrubs with an upright growth habit. They produce showy cone-shaped flower panicles in late summer when few other shrubs are in bloom. These panicles can reach up to 7 inches in length and feature clusters of small, creamy white blooms that gradually turn pinkish and eventually fade to tan or brown in the fall.
Tree hydrangeas are relatively easy to grow and can thrive in a variety of conditions. They are tolerant of pollution, salt, and urban environments. They prefer moist but well-drained soil with an acidic to neutral pH. These shrubs require full to partial sunlight, with some afternoon shade in hot climates.
Planting and Care
The best time to plant tree hydrangeas is in the spring or early fall. Choose a planting site with good drainage and protect the plants from strong winds, which can damage their stems.
Water tree hydrangeas regularly, especially during hot and dry weather. Avoid overwatering, as this can lead to root rot and other diseases. Fertilize the shrubs twice a year, once in early spring and again in the fall after the flowers have faded. Use a fertilizer formulated for shrubs and trees.
Pruning and Training
Tree hydrangeas can be trained to grow as small trees by judicious pruning. However, they achieve their best form when grown as large shrubs with multiple stems. Blooms occur on the current season’s growth, so prune as needed in the late winter to early spring. Untimely pruning can sacrifice some of the flowers for that growing season.
To train a tree hydrangea to grow as a tree, choose one main stem and secure it to a sturdy stake. Remove any competing ground stems and shoots that emerge from the main stem. Continuously check for shoots around the base of the plant and remove them as they appear. The main stem will eventually form a trunk-like structure.
Propagation
Tree hydrangeas can be propagated by cuttings. The best time to do this is in the spring or early summer before the plant begins to flower. Choose a healthy stem that has not yet flowered and cut off a piece that’s about 6 inches long. Remove the lower leaves and cut the remaining leaves in half. Dip the cutting in rooting hormone and plant it in a small container filled with vermiculite, coarse sand, or a combination of the two. Keep the soil moist but not soggy and place the container in a bright but indirect light. The cutting should develop a root system within a month.
Overwintering
To help tree hydrangeas through the winter, keep the soil moist right up until the ground freezes. Cover the roots with 3 to 4 inches of mulch, taking care to remove it as soon as the temperatures warm up.
Pests and Diseases
Tree hydrangeas are generally resistant to pests and diseases. However, they can be susceptible to aphids, rose chafers, scale, slugs, and snails. Organic pesticides can be used to control these pests. Fungal diseases such as powdery mildew, blight, and leaf spot can also affect tree hydrangeas. These diseases can be treated with an appropriate fungicide.
Troubleshooting
Leaves Turning Black/Brown: This can be a sign of a fungal disease. Prune off the affected area or use a suitable fungicide.
Leaves Turning Yellow: This can indicate overwatering, underwatering, or a nutrient deficiency. Adjust watering practices and fertilize as needed.
FAQs
What is the difference between tree hydrangeas and hydrangea bushes?
Tree hydrangeas are shrubs that have an upright growth habit and can be trained into a tree-like form. Hydrangea bushes are typically shorter and more compact.
Can tree hydrangeas grow indoors?
Tree hydrangeas can be grown as container plants indoors, but they may not reach their full potential in terms of size and flowering.
How should I prune my tree hydrangea to encourage flowering?
Prune tree hydrangeas in the late winter to early spring, removing any dead or damaged stems. Cut back the remaining stems to about 6 inches above the ground. This will encourage the growth of new stems that will produce flowers in the summer.