How to Grow & Care for Smooth Hydrangea (Hydrangea arborescens)

Hydrangeas are popular and easily recognizable shrubs with impressive flowers. A large genus of plants, there are only a handful of species commonly grown in garden landscapes. The smooth hydrangea (Hydrangea arborescens), sometimes called Wild hydrangea, is one of those species. These fast-growing, compact shrubs are best planted in the fall and don't often grow above five feet. They require partial shade and well-draining soil. All parts of hydrangea plants are toxic to people and pets. Read on for our care and growing guide.

Smooth Hydrangea Care

Here are the main growing requirements for a smooth hydrangea:

• Plant the shrubs at least five feet apart
• Need partial shade
• Requires well-draining soil

Light

As with most hydrangea species (Hydrangea arborescens) prefers a partial shade location with dappled sunlight. It can cope with full sun, but shade from the afternoon sun is important in hot southern regions.

Soil

Smooth hydrangeas are adaptable and tolerant of poor soil conditions providing they are moist and well-drained. To thrive, they prefer loamy, rich, acidic soils.

Water

If you live in a region with hot, dry summers or your shrub is growing in the north in full sun, you'll need to provide your smooth hydrangea with supplemental irrigation during the growing season. It needs moist conditions, and a layer of mulch to help retain moisture.

Temperature and Humidity

Smooth hydrangeas are one of the most cold-hardy hydrangea species and don't generally need additional winter protection. However, they can die back when winters are particularly cold. The ideal daytime temperatures are around 70 degrees Fahrenheit during the growing season. They prefer humidity over dry areas and should be protected from winds.

Fertilizer

Smooth hydrangeas do well being fed a balanced, all-purpose fertilizer. If you want to increase the number of blooms and their size, select a feed higher in phosphorous, such as one labelled "bloom boost" or with a balance of 10-20-20. Spring feeding is particularly important. Too much fertilizer, however, can burn or yellow the foliage, and too much nitrogen encourages foliage growth rather than blooms.

Unlike Big Leaf hydrangeas, the bloom color of the smooth hydrangea cannot be manipulated by raising or lowering soil PH.

Types of Smooth Hydrangea

There are many showy Hydrangea arborescens cultivars to choose from. Some popular options include:

• Incrediball hydrangea (Hydrangea arborescens 'Abetwo' Incrediball) : Has abundant, spectacular huge flowers and strong, upright stems.
• Invincibelle Spirit hydrangea (Hydrangea arborescens 'NCHA1 Invincibelle Spirit') : What makes this cultivar stand out is that the blooms are pink rather than the standard white color.
• Hydrangea arborescens (Hayes Starburst) : This cultivar stands out because the blooms are pink rather than the standard white color.

Pruning

Because they bloom on new wood, pruning smooth hydrangeas is easy. Plants can be pruned to the ground every winter or early spring to promote healthy new stem growth and uniform flower production. Alternatively, simply remove any weak or damaged stems.

Propagating Smooth Hydrangea

This fast-growing hydrangea suits propagation from cuttings—root or stem. To propagate softwood cuttings, follow these steps (as long as it's not a trademarked cultivar):

1. Take a 5-inch stem cutting and remove the lower leaves
2. Dip the cutting in rooting hormone
3. Use a sterile, well-drained potting medium such as damp sand or vermiculite and keep it moist
4. Cover loosely with plastic, so it does not press against the leaves
5. Keep in bright but indirect sunlight and water whenever the soil starts to dry
6. Roots should develop within a few weeks

Overwintering

Smooth hydrangeas will go dormant in the winter. If grown outdoors, you'll need to wrap and cover to protect the plant and root system. Hydrangeas grown in pots can be brought indoors or into a greenhouse during the cooler months. Water once a month to keep roots moist until the plant grows again in the spring.

Common Pests & Plant Diseases

Smooth hydrangeas don't have problems with any serious pests or diseases, but some common garden pests are attracted to the plants. Keep an eye out for things like aphids, Japanese beetles and spider mites.

The common fungal disease powdery mildew can also sometimes be an issue because the plant prefers higher humidity and moisture.

How to Get Smooth Hydrangea to Bloom

Bloom Months

With a long bloom period, the smooth hydrangea flowers bloom prolifically throughout the summer.

What Do Smooth Hydrangea Blooms Look and Smell Like?

Smooth hydrangea produces clusters of tiny white, sweet-scented flowers. The flowerheads can grow as large as 12 inches wide and are attractive to pollinators.

How to Encourage More Blooms

To encourage healthy, uniform blooms, pruning in the winter is helpful. Too much or too little sun can also impact bloom success, so pick the right location for your smooth hydrangea. And don't forget to avoid high nitrogen fertilizer, which encourages more foliage than flowers.

Common Growing Problems

There are a few common growing issues to be aware of when growing smooth hydrangea.

Yellowing Leaves

If you notice your smooth hydrangea has yellow leaves, it might be due to a nutrient deficiency (in particular a lack of chlorophyll production due to low iron). Fertilize with iron-enriched fertilizer and make sure the soil is kept acidic.

Drooping Leaves

A smooth hydrangea's leaves can droop if the plant has too much moisture or too much sun exposure. Ensure optimum levels of each in order to keep your plant healthy and strong.