Mountain Hydrangea
The Tougher Hydrangea
This reliable hydrangea resists frost damage and blooms all summer long.
The mountain hydrangea (Hydrangea serrata) is a compact, upright deciduous shrub belonging to the Hydrangeaceae family, and is native to the mountainous regions of Korea and Japan. It has delicate lacecap or mophead flower clusters ranging in color from blue to pink, depending on the soil pH. Mountain hydrangeas are hardy in zones 6-9 and reach a mature size of 2-6 feet high and wide, depending on the cultivar.
In recent years, as temperature fluctuations in late winter and early spring have become more problematic for the bigleaf hydrangea (Hydrangea macrophylla), gardeners are reconsidering the mountain hydrangea as a tougher, more dependable addition to the garden. Due to their longer period of dormancy and later bloom time, mountain hydrangeas are less susceptible to frost damage and more likely to flower consistently from summer until early fall. They grow best when planted in partial shade and cool, moist, rich soil mimicking their native environment. Mountain hydrangeas have small leaves and do not wilt as easily as their bigleaf cousins, yet still prefer to be kept out of harsh afternoon sun. As an added bonus, the dark green, serrated leaves of the mountain hydrangea turn stunning shades of burgundy and red in autumn.
Mountain hydrangeas are relatively unbothered by diseases and insect pests. Like all hydrangeas, they can develop fungal problems when overwatered. Deer will eat hydrangea flower buds and leaves, especially the tender young growth. If you would like to grow a flowering shrub that deer tend to leave alone, try Ruby Spice summersweet clethra as a deer resistant alternative to the bigleaf hydrangea.
Photo credit: Don Coombez
How to Plant and Grow Mountain Hydrangea
Planting: The best time of year to plant a mountain hydrangea is in the spring or fall, giving the roots time to establish before the onset of extreme hot or cold weather. Water deeply immediately after planting.
Location: Choose a location with well-drained soil that is rich in organic matter. Mountain hydrangeas prefer soil that retains moisture but does not become waterlogged. Select a spot with partial shade - while mountain hydrangea can tolerate full sun, it prefers partial shade and protection from the intense afternoon sun.
Soil: Amend the soil with organic matter, such as compost, shredded leaves, or Leaf-gro®, to improve drainage and soil fertility. If you would like your mountain hydrangea to bloom specifically pink or blue, consider getting a soil test and adding either sulfur or lime to the soil. Add sulfur for blue flowers and lime for pink blooms.
Mulch: Apply a layer of organic mulch around the base of the plant to retain soil moisture, regulate temperature, and suppress weeds.
Watering: Keep the soil consistently moist but not waterlogged, especially during periods of drought. Deep watering is preferable to encourage the development of a strong root system (Are you in a drought? Check the U.S. Drought Monitor).
Fertilization: Hydrangeas typically do not need fertilization when they are given the rich, fertile soil they prefer. Each spring, spread a layer of compost, shredded leaves or Leaf-gro® around the base of your hydrangea, being careful to keep it away from the base of the shrub.
Pruning: Mountain hydrangeas bloom on old wood and look their best with minimal pruning. If needed, prune to shape in late summer when flowering has finished. Avoid pruning in fall, winter, or early spring as you risk removing flower buds and diminished flowering. Do not cut back mountain hydrangeas in the fall.
Pest and Diseases: Mountain hydrangeas are relatively pest resistant; aphids are an occasional problem. Mountain hydrangeas are prone to powdery mildew and leaf spot - ensure good air circulation to minimize the risk of diseases, and practice good watering habits (see “How to Water your Plants” to brush up on your watering skills).
Do Mountain Hydrangeas Like Sun or Shade?
Mountain hydrangeas thrive in partial shade (2 - 4 hours of direct sunlight per day). While they can tolerate some sunlight, mountain hydrangeas prefer dappled or filtered light, with protection from the intense hot afternoon sun. In hot climates, providing them with morning sun and afternoon shade can help prevent their flowers and leaves from wilting and scorching. In cooler regions, they may tolerate more sun, but protection from harsh afternoon sunlight is still recommended.
Mountain hydrangeas (Hydrangea serrata) stand up to heat, humidity, and late spring frosts.
Landscaping Ideas for Mountain Hydrangea
Mixed Border Planting: Create a mixed border planting with mountain hydrangeas along with other complementary shade-loving plants such as astilbe, ferns, and Japanese forest grass. This will add layers of texture and color to your garden.
Woodland Garden: Incorporate mountain hydrangeas into a woodland garden setting. Under the dappled shade of trees, these hydrangeas will thrive and provide a provide flowers all summer long.
Container Gardening: Use larger containers, pots, or planters to showcase mountain hydrangeas in a shadier corner of a patio, deck or front porch.
Accent Planting: Use mountain hydrangeas as accent plants to highlight certain areas of the garden. Planting near a water feature or along a pathway can draw attention to these beautiful shrubs.
Foundation Planting: Incorporate mountain hydrangeas into your foundation planting to add visual interest and soften the lines of your home. They work well when paired with partial-shade loving evergreen shrubs like Himalayan sweetbox (Sarcococca hookeriana var. humilis) or spreading Japanese plum yew.
Mass Planting: Create a striking display by mass planting mountain hydrangeas in larger garden areas, like a shady slope or property line. Soften a wooden fence with a row of mountain hydrangeas running along the length, or fill up a shaded side yard with a mass planting of mountain hydrangeas next to a stepping stone pathway.
Photo credit: Al Soot
How to Change Hydrangea Color
You can change the color of your mountain hydrangea blooms by manipulating the pH of the soil. The pH level affects the availability of aluminum in the soil, in turn influencing the color or hydrangea flowers. Adding aluminum sulfate, garden sulfur, or organic matter makes the soil more acidic and will turn bigleaf hydrangea blooms blue. Adding garden lime raises the soil pH and turns blooms pink. Be patient - it can take months for change to become evident!
Different Types of Mountain Hydrangea
Bluebird (Hydrangea serrata ‘Bluebird’): A classic cultivar with blue to purple-pink lace cap flowers, growing up to 6 feet tall and wide. Vigorous grower with brilliant red fall color. Zones 6-9.
Pink Dynamo® (Hydrangea serrata ‘JPD01’ Pink Dynamo®): Heavily blooming, 3-foot high and wide flat-topped shrub with hot pink flowers and dark greenish black leaves. Zones 5-9.
Tiny Tuff Stuff™ (Hydrangea serrata ‘MAKD’ Tiny Tuff Stuff™): Profuse soft pink or blue lacecap flowers top a compact, 1-2 foot high and wide shrub. Zones 5-9.
Tuff Stuff™ (Hydrangea serrata ‘MAK20’ Tuff Stuff™): A reblooming cultivar, bred for cold hardiness, that blooms on old and new wood. It has semi-double reddish pink to blue flowers and grows 2-3 feet high and wide. Hardy in zones 5-9.
Tuff Stuff™ Ah-ha® (Hydrangea serrata ‘SMNHSDD’ Tuff Stuff™ Ah-ha®): Pink to blue lacecap flowers with florets resembling waterlilies. This prolific rebloomer has improved cold resistance and flowers on old and new wood. Grows 2-3 feet tall and wide. Zones 5-9.
Tuff Stuff™ Red (Hydrangea serrata ‘SMNMAKTSR’ Tuff Stuff™ Red): Dark pink to red, double lacecap flowers bloom on both old and new wood. This compact shrub has deep green leaves and grows 2-3 feet tall and wide. Zones 5-9.
Tuff Stuff™ Top Fun (Hydrangea serrata ‘SMNHSG’): Prolific, showy, reblooming hot pink or purple lacecap flowers top dark green foliage. A tidy 2-3 foot tall and wide plant with improved cold resistance. Zones 4-9.
Twirligig™ (Hydrangea serrata ‘Shojo’ Twirligig™): Deep pink to blue single lacecap flowers top strong stems. Grows 4-5 feet tall and wide. Zones 5-9.
Are Mountain Hydrangeas Poisonous to Dogs?
Mountain hydrangeas (Hydrangea serrata) contain compounds that can be toxic to dogs if ingested, specifically cyanogenic glycosides. These compounds can release cyanide when broken down in the digestive system. However, the level of toxins in mountain hydrangeas are relatively low, and instances of dogs getting poisoned by consuming these plants are rare.
While the risk of severe poisoning is low, it’s important to monitor your dog's behavior in outdoor spaces. If you suspect your dog has ingested a toxic plant, seek immediate veterinary care or contact the Pet Poison Hotline (read “Which Plants are Toxic to Dogs” for more information).