How to Grow Smooth Hydrangea (Hydrangea arborescens)

Smooth hydrangea shrub with white and light yellow flower clusters

The Spruce / Evgeniya Vlasova

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. All parts of hydrangea plants are toxic to people and pets.

Common Name Smooth hydrangea, Wild hydrangea
Botanical Name Hydrangea arborescens
 Family Hydrangeaceae
 Plant Type Deciduous, Shrub
 Mature Size 3 -10 ft. tall
 Sun Exposure Partial shade
 Soil Type Well-drained
 Soil pH Acid, Neutral, Alkaline
 Bloom Time Summer
 Flower Color White
Hardiness Zones 3-9, USA
 Native Area Eastern USA
Toxicity Toxic to people and pets

Smooth Hydrangea Care

Smooth hydrangeas sucker easily and can spread over large areas, working well for erosion control. Plant the shrubs at least five feet apart. Grown in masses in partly shaded areas, they create an impressive privacy hedge and look good at the back of a perennial border.

Smooth hydrangea shrub with bright pink flowers clusters with large leaves in sunlight

The Spruce / Evgeniya Vlasova

Smooth hydrangea shrub with large leaves and white flower clusters

The Spruce / Evgeniya Vlasova

Smooth hydrangea shrub with pink flower clusters in sunlight

The Spruce / Evgeniya Vlasova

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

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 aphidsJapanese 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

With a long bloom period, the clusters of tiny white, sweet-scented flowers bloom prolifically throughout the summer. The flowerheads can grow as large as 12 inches wide and are attractive to pollinators.

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.


FAQ
  • How long can smooth hydrangea live?

    These shrubs are fast-growing and not terribly long-lived, but they can live up to 20 years with the right conditions and care.

  • What’s the difference between smooth hydrangea and panicle hydrangea?

    Another of the main hydrangea species, panicle hydrangeas (Hydrangea paniculata) are quite different from smooth hydrangeas in appearance. They grow much taller—sometimes up to 15 feet tall. Their flowers, which bloom in late summer, have a unique cone shape rather than the round balls of most other hydrangea species.

  • How fast do smooth hydrangea grow?

    This species grows as much as 25 inches annually and reach full size in as little as three years.

Article Sources
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  1. Hydrangea arborescens (Hills of snow, hortensia, hydrangea, sevenbark, seven bark, smooth hydrangea, wild hydrangea) | North Carolina Extension Officer Gardener Plant Toolbox.