Tree hydrangeas (Hydrangea paniculata), also known as panicle hydrangeas, are a fast-growing flowering shrub with an upright growth habit. These plants provide late summer blossoms when few other bushes are in bloom. The shrub has oval, toothed, dark green leaves, and it produces cone-shaped flower panicles that stretch around 7 inches long with clusters of small, creamy white blooms. The flower heads take on a pinkish hue over time before fading to tan or brown for the winter. Tree hydrangeas can be planted in the spring after the threat of frost has passed, as well as in the early fall.
|Botanical Name||Hydrangea paniculata|
|Common Names||Tree hydrangea, panicle hydrangea, peegee hydrangea|
|Mature Size||8–15 ft. tall, 6–12 ft. wide|
|Sun Exposure||Full, partial|
|Soil Type||Loamy, well-drained|
|Soil pH||Acidic, neutral|
|Flower Color||White, pink|
|Hardiness Zones||3–8 (USDA)|
|Toxicity||Toxic to people, animals|
Tree Hydrangea Care
Tree hydrangeas are fairly easy to care for and can grow in a variety of conditions. They are tolerant to pollution and urban conditions, as well as to salt in the soil. So they can handle being planted near roadways. Just make sure your planting site has good soil drainage and is sheltered from strong winds, which can damage the stems.
These shrubs also don’t typically have many pest or disease problems, especially when they’re grown in an environment they like. You might occasionally see aphids or mites on the foliage, which often can be mitigated with a strong blast of water from the hose. Expect to water and feed your shrub regularly, and prune to maintain its shape.
Tree hydrangeas grow well in full sun to partial shade, meaning at least four hours of direct sunlight on most days. In hot climates, they will benefit from some afternoon shade.
These shrubs can handle a variety of soil types, including sandy, loamy, and even clay provided that there is good drainage. They prefer an organically rich soil with a slightly acidic to neutral soil pH, though they also can tolerate slightly alkaline soil.
Tree hydrangeas thrive in lightly moist but not soggy soil. Be careful not to overwater, which can cause root rot and other diseases. However, allowing the soil to dry out too much can cause the foliage to wilt and eventually damage or kill the plant.
Temperature and Humidity
These plants have good cold tolerance within their growing zones, especially compared to many other hydrangea species. In hot weather, it’s important to make sure they are well-watered to prevent stress on the plant. Humidity typically isn’t an issue as long as their water requirements are met.
Feed tree hydrangeas twice a year in the early spring and in the fall immediately after the flowers have faded, using a fertilizer for shrubs and trees. Over the summer, the shrubs will benefit from an application of compost.
Are Tree Hydrangeas Toxic?
All parts of the plant are toxic to humans and animals when ingested. They contain the chemical amygdalin, which produces cyanide when it’s metabolized in the body. Higher concentrations are found in the leaves and flowers (including the flower buds) of the plant.
Symptoms of Poisoning
Symptoms of toxicity include nausea, vomiting, stomach pain, diarrhea, lethargy, and confusion. The symptoms typically come on quickly. Contact a medical professional as soon as possible if you suspect poisoning.
Tree Hydrangea Varieties
There are several varieties of tree hydrangeas, including:
- Hydrangea paniculata 'Grandiflora' grows to 25 feet with a 10-foot spread and has pure white flowers.
- Hydrangea paniculata 'Limelight' grows 6 to 8 feet tall and 5 to 7 feet wide and has a greenish color in its flowers.
- Hydrangea paniculata 'Big Ben' grows 6 to 8 feet tall and 5 to 7 feet wide and is valued for having flowers of a deeper pink color.
- Hydrangea paniculata 'Bobo' is a dwarf variety, growing only about 3 feet tall and wide.
- Hydrangea paniculata 'Pinky Winky' grows to a maximum height and width of 8 feet and is known for its bicolor flower heads (pink on the bottom, white on the top).
This plant can be trained to grow as a small tree by judicious pruning. But it achieves its best form when grown as a large shrub with multiple stems. Blooms occur on the current season’s growth (new wood), so prune as needed in the late winter to early spring. Untimely pruning can sacrifice some of the flowers for that growing season. When kept in its shrub form, the shrub will bear larger flower clusters if you thin it to five to 10 primary stems.
To train the plant to grow as a tree, choose one main stem to secure to a sturdy stake. Prune away competing ground stems. And remove any shoots that emerge from your main stem from the ground to about three-quarters of the way up that stem. Continuously check for shoots around the base of the plant, and remove them as they pop up. Your main stem will continue to grow with foliage at the top, taking on the look of a trunk. It can require two or more years before a true tree shape is accomplished.