How to Grow and Care for Tree Hydrangeas (Panicle Hydrangeas)

Tree hydrangeas, or panicle hydrangeas, are fast-growing flowering shrubs with an upright growth habit and cone-shaped flower panicles of creamy white blooms. These plants provide late summer blossoms when few other bushes are in bloom. Tree hydrangeas are fairly easy to care for and can grow in various conditions. They are tolerant of pollution, urban conditions, and salt in the soil. Note that they are toxic to both humans and animals. Learn how to grow a tree hydrangea for beautiful blooms.

Tree Hydrangea Care

Here are the main care requirements for growing a tree hydrangea.

• Plant tree hydrangeas in the spring or early fall.
• Place tree hydrangeas in well-draining, acidic soil.
• Water a tree hydrangea so the soil stays slightly moist.
• Fertilize tree hydrangeas regularly.
• Shelter tree hydrangeas from strong winds, which can damage the stems.

Light

Tree hydrangeas grow well in full sun to partial shade, needing at least four hours of direct sunlight on most days. In hot climates, they will benefit from some afternoon shade.

Soil

The tree hydrangea shrub can handle many soil types, including sandy, loamy, and even clay, if it has good drainage. This shrub prefers organically rich soil with a slightly acidic to neutral soil pH, though it also can tolerate slightly alkaline soil.

Water

Water the soil so it is lightly moist but not too soggy. 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

Compared to many other hydrangea species, tree hydrangeas have good cold tolerance within their growing zones. 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.

Fertilizer

Feed tree hydrangeas twice a year in the early spring and in the fall immediately after the flowers have faded, using a fertilizer formulated for shrubs and trees. Over the summer, the shrubs will benefit from an application of compost.

Types of Tree Hydrangea

There are several varieties of tree hydrangeas:

• Hydrangea paniculata 'Grandiflora': This type of tree hydrangea grows to 25 feet with a 10-foot spread and has pure white flowers.
• Hydrangea paniculata 'Limelight': This pretty tree hydrangea grows 6 to 8 feet tall and 5 to 7 feet wide and has greenish color in its flowers.
• Hydrangea paniculata 'Big Ben': This type grows6 to 8 feet tall and 5 to 7 feet wide and is valued for having flowers of a deeper pink color.
• Hydrangea paniculata 'Bobo': This dwarf variety of tree hydrangea grows only about 3 feet tall and wide.
• Hydrangea paniculata 'Pinky Winky': This beautiful type of tree hydrangea 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).

Pruning

Train a tree hydrangea to grow as a small tree by judicious pruning. The plant will, however, achieve its best form when it is grown as a large shrub with multiple stems.

Blooms occur on the current season’s growth (new wood), so prune as needed in late winter to early spring. Untimely pruning can sacrifice some of the flowers for that growing season. When kept in its shrubby form, it will bear larger flower clusters if you thin it to five to 10 primary stems.

Train the plant to grow as a tree by choosing one main stem to secure onto a sturdy stake. Prune away competing ground stems. Continuously check and remove shoots that emerge from your main stem from the base to three-quarters of the way up the stem. 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 tree hydrangea takes a true tree shape.

Propagating Tree Hydrangea

Though it is possible to grow tree hydrangeas from seed, it is difficult and rarely attempted by gardeners. Propagate tree hydrangeas by taking cuttings in the spring or early summer before the shrub begins to flower. Taking a cutting is an inexpensive way to produce more of a particular tree hydrangea variety that you like. Here's how:

1. Choose a healthy stem that has not flowered yet, and cut off a piece that's about 6 inches long with sharp, sterile pruners.
2. Remove the lower leaves on the cutting, and cut the other leaves to half their length.
3. Dip the cutting in rooting hormone, and immediately plant it in a small container filled with vermiculite, coarse sand, or a combination of the two.
4. Water the cutting well, making sure the soil is moist but not overly wet. Place a plastic bag or dome over the container to retain moisture, making sure the plastic doesn't touch the cutting.
5. Place the container in an area with bright but indirect light. Keep the soil lightly moist but not soggy. Expect the cutting to take about a month to develop a root system, and it will be ready to transplant.
   

Potting and Repotting Tree Hydrangea

Container-grown tree hydrangeas usually need to be repotted every year or two as they grow, depending on your pot size. The best time to repot hydrangeas is during the spring when the plant is no longer dormant but isn't yet stressed from the heat of summer. You can also repot a hydrangea during the winter to allow it more time to adjust to its new surroundings.

Choose a container a few inches larger than the previous one. If you are potting a tree hydrangea for the first time, go with a pot of 8 to 12 inches in diameter. The best container material is unglazed clay, which allows excess moisture in the soil to evaporate through its walls.

Use a well-mixed compost with a fertilizer designed for hydrangeas. Cover the roots and stem with the soil. Keep the container in the shade for the first few days, gradually introducing it to more sun to acclimate the plant to the light and humidity. Keep the soil moist but not waterlogged.

Overwintering

Help your plants through the winter by keeping the soil moist until the ground freezes. Cover the roots with 3 to 4 inches of mulch and remove it as soon as the temperature warms up.

Common Pests & Plant Diseases

You might see aphids or mites on a tree hydrangea's foliage, which often can be mitigated with a strong blast of water from a garden hose. Hydrangeas of all varieties can also fall prey to rose chafers and scale. Organic pesticides can help get rid of these pests. Remove slugs and snails by hand, natural methods, or use slug pellets for heavier infestations.

Hydrangeas are prone to fungal diseases, such as powdery mildew, blight, and leaf spot, all of which can be treated with an appropriate fungicide. Numerous viruses cause leaves to turn yellow and a plant to lose its flowers. The only real treatment is the removal of affected plants.

How to Get Tree Hydrangea to Bloom

Bloom Months

Tree hydrangeas are late-season bloomers that flower midsummer or late summer (July or August) and can continue through the fall until frost develops.

What do Tree Hydrangea Flowers Look and Smell Like?

The tree hydrangea 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. The flowers on a tree hydrangea feature rays of four to five petals that measure around 1 to 3 inches across. Tree hydrangea flowers can have a heady perfume-like scent.

How to Encourage More Blooms

Deadheading (removing spent blooms) encourages further flowering, though many gardeners opt to leave the dried flower panicles on the plants through winter for visual interest in the garden.

Ensure the ground is moist but not soggy for your tree hydrangea to bloom. Hydrangeas also need some sunlight, but not too much, so keep them out of harsh light if you live in a hot climate. Hydrangeas bloom better when they live in more acidic soil, so test your soil to see whether amendments are necessary. Also, overfertilization can lead to lush foliage but fewer blooms.

Common Problems With Tree Hydrangea

Tree hydrangeas do not typically have many pest or disease problems, and they are fairly easy to care for as long as growing conditions are right. The following are some common issues to watch out for.

Leaves Turning Black/Brown

Black or brown spots on foliage can often signal a fungal disease. If the affected area is small, just prune it off. Use a suitable fungicide for larger problems.

Leaves Turning Yellow

Yellow foliage on a hydrangea of any kind can often be a sign of unsuitable conditions, such as overwatering or underwatering. The soil should never be soggy or allowed to dry out completely. A hydrangea tree's yellowing leaves can also indicate that too much fertilizer was used or that there's a nutrient deficiency, such as iron.

From: thespruce