Plants

Smooth Hydrangea, Shrub Hydrangea

Hydrangea arborescens ‘Annabelle’

Folkert Siemens Folkert Siemens

Fans of the Smooth Hydrangea are growing day by day — the “Annabelle” variety is quite popular. This is how you plant and care for the beautiful flowering shrubs.

Growth type
  • Small shrub
Growth height (from)
from 100 cm to 150 cm
Growth width (from)
from 150 cm to 200 cm
Growth characteristics
  • upright
  • foothills
Flower color
  • green
  • white
Flowering time (month)
  • June to September
Flower shape
  • Panicules
  • Umbrella panicles
Leaf color
  • green
page format
  • ovate
  • elliptiques
  • pointed
Light
  • sunny
  • semi-shade to shady
Soil type
  • sandy to loamy
Soil Moisture
  • fresh to humid
ph value
  • neutral to acidic
Lime compatibility
  • sensitive to lime
Nutrient requirements
  • moderately nutritious
Humus
  • rich in humus
Decorative or utility value
  • Flower Decoration
Winter Hardness
  • hardy
Use
  • Bouquets
  • Group planting
  • Planters
  • Rose companion
Garden style
  • cottage garden
  • Flower garden
  • Formal garden
  • Rhododendron garden
  • Rose Garden
  • Pot garden
  • Forest Garden

Origin

The Smooth Hydrangeas are also commercially available as wild Hydrangeas. The wild species is native to the Appalachian Mountains, a north-south mountain range in the eastern United States. It is also found in the Delaware River valley. However, the wild Smooth Hydrangea is not cultivated as a garden plant. We only sell selected varieties that have particularly large, sterile inflorescences and that are suitable for gardens.

The most popular is the very large-flowered ‘Annabelle’ variety, a wild plant which, according to legend, was discovered by Hariett Kirkpatrick, the owner of the Anna Pottery earthenware factory in southern Illinois, during a horse ride in 1910. She planted what she found in the garden of the company premises and here the Hydrangea grew undisturbed for 50 years before Dr. J. C. McDaniel, plant breeder and associate at the University of Illinois, found out about them in the 1960s. He named it - in honor of the long-defunct Anna Pottery company - ‘Annabelle’.

Smooth Hydrangea arborescens ‘Annabelle’

Smooth Hydrangea arborescens ‘Annabelle’

Growth

The Smooth Hydrangea is an upright shrub that grows up to 78.74 inches high with numerous basal shoots. The twigs are remarkably thin and have an ocher yellow bark which later turns red to dark brown. Snowball Hydrangeas spread underground through short runners, so old shrubs can take up a lot of space over the years.

Leaves

The light green, opposite leaves are ovate to elliptical and pointed at the end. They can be 3.14 inches to 5.90 inches long and have a matte surface. The plants shed their leaves at the end of the season, which means that the fall colors do not form.

Blossoms

From a botanical point of view, the large, flat flower panicles are called umbrella panicles. They appear from the end of June to September at the ends of the new shoots and consist of numerous sterile single flowers that are initially greenish-white, which later turn into creamy white. As they fade, they take on a lime green hue and can be used as decorations even when they dry out. The ‘Annabelle’ variety is still one of the most blooming and large-flowered selections. It is not uncommon to see flowers of up to 9.84 inches in diameter.

Smooth Hydrangeas as vase decorations

The flower stalks of the Smooth Hydrangea are also popular as vase decorations

Fruit

Since the flowers are usually sterile, ‘Annabelle’ and most of the other varieties do not grow fruit.

Location and Soil

Smooth Hydrangeas grow in sunny to shaded locations, which should be protected from wind and if possible, from rain as well. A larger tree is ideal as a shade, which also reduces the impact of very heavy rainfall. In heavy rain, the flowers quickly become so heavy that the flower stalks buckle and the whole shrub literally falls apart. Usually, however, it will straighten up on its own after a while. As with all Hydrangeas the soil should be loose and sufficiently moist with lowest possible lime content along with being rich in humus. A pH-value between 5.5 and 6 is ideal.

Planting and Care

Smooth Hydrangeas are among the most frost hardy Hydrangeas and can withstand cold winters without any problems. Therefore, unlike the more sensitive Mophead Hydrangeas, it is not necessary to plant Smooth Hydrangeas as early as spring. Planting in fall is also no problem for them. Prepare the soil thoroughly using deciduous humus or sand if required. Since Smooth Hydrangeas, like all Hydrangeas, have a high water requirement, a slightly shaded location is better than one in full sun. In any case, the freshly planted shrubs should be kept properly damp for the first few weeks. Mulch the soil with a layer of leaves or, bark mulch after scattering a few handfuls of horn shavings around the root.

Avoid using garden compost to fertilize Smooth Hydrangeas, as it often contains too much lime. It is best to sprinkle horn shavings in spring or feed the plants with Rhododendron fertilizer. You can also use Hydrangea fertilizer, but it is usually more expensive, as it is often enriched with alum to color Mophead Hydrangeas. However, this does not affect the colors of the Smooth Hydrangea flowers. In particular, the large-flowered ‘Annabelle’ will eventually need perennial support. Alternatively, you can stabilize the shoots individually with bamboo sticks so that they do not buckle under the heavy flowers.

Pruning

Unlike the Mophead Hydrangea, in which only the old inflorescences are removed, the Smooth Hydrangeas can be cut back to just above the ground at the end of February. They then sprout particularly vigorously and form large inflorescences. Avoid strong pruning in very windy locations. The long new shoots are not very stable and the flower heads droop after rain showers. If pruning is less rigorous, the flowers remain a little smaller and the entire branch structure is more stable.

Video: How to Prune Hydrangeas

Provided that you know which Hydrangeas are growing in the garden, you can’t go awfully wrong when it comes to pruning. In our video, we show you how to prune the different species.

Where to plant

The flowering shrubs are usually integrated individually or in groups in perennial plantings in sunny to partially shaded locations. Smooth Hydrangeas go very well with large-leaved ornamental perennials such as Rodgersia, Astilbes, Monkshood, Globe Thistles (echinops), High Sedum and ornamental grasses. In addition, the low shrubs cut a fine figure as lush flower hedges.

Smooth Hydrangeas and Astilbes

Smooth Hydrangeas go very well with tall Astilbes

In the shade, they harmonize beautifully with different ferns. When planted together, they go well with Japanese Dwarf Spars (Spiraea japonica), dark leaved Smooth Japanese Maple and of course, all other varieties of Hydrangeas. Smooth Hydrangeas can even be combined with yellow or white roses in locations that are not too shady. An insider tip from us, — planting the ‘Rhapsody in Blue’ variety with its purple flowers. Smooth Hydrangeas create beautiful contrasts with properly cut topiary trees such as boxwood — this is why they are also very popular in formal gardens.

Smooth Hydrangeas are also suitable for growing in pots on the patio or balcony, as they remain relatively compact with a height of around 59.05 inches. However, the pot needs a lot of soil so that the it does not dry out too quickly on sunny days.

Other varieties

  • “Grandiflora”: Another classic along with ‘Annabelle’— it is a bit more vigorous and stable, but has smaller flowers
  • “Pink Annabelle”: As the name suggests, it is an ‘Annabelle’-type variety with light pink flower balls. It is also sold under the name ‘Invincible spirit’
  • ‘Strong Annabelle’: It grows more compact, has slightly smaller flower balls than the real ‘Annabelle’ and is therefore considered more stable
  • ‘Incrediball’: the variety with the largest inflorescences to date. They form a beautiful hemisphere and can reach up to 11.81 inches in diameter. In terms of color, they hardly differ from ‘Annabelle’ but are a little whiter during the main flowering period

Smooth Hydrangeas ‘Pink Annabelle’ (left) and ‘Incrediball’ (right)

Propagation

All smooth Hydrangeas are easy to propagate in early summer by half-woody cuttings. It is also possible to propagate with hardwood cuttings in winter, and new plants can even be obtained by dividing — in other words, cutting off the runners in fall or spring.

Diseases and Pests

The Smooth Hydrangeas suffer less from incurable viral infections than the Mophead Hydrangeas. Leaf spot diseases and powdery mildew occur occasionally. The most common pests include scallop insects and vine weevils.

Frequently Asked Questions

What does a Smooth Hydrangea look like?

Smooth Hydrangeas are upright shrubs that are mainly characterized by their large, mostly greenish-white flower panicles. The flowers of the popular ‘Annabelle’ variety often have a diameter of up to 9.84 inches.

How big does the Smooth Hydrangea get?

Smooth Hydrangeas can grow up to 2.18 yards high.

How long does the Smooth Hydrangea bloom?

Smooth Hydrangeas usually bloom from late June to September.

Where does the Smooth Hydrangea grow?

Smooth Hydrangeas like to grow on low-lime, humus-rich soil that is sufficiently loose and moist. The location can be sunny or shaded, but should be protected from the wind.

When can you prune Smooth Hydrangeas?

Pruning Hydrangeas is recommended in late February.

How to prune the Smooth Hydrangea?

Prune the Smooth Hydrangeas close to the ground. If the location is very windy, however, it is better not to cut it back drastically.

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