Hydrangea

Revised by Joey Williamson, HGIC Horticulture Extension Agent, Clemson University (10/14). Originally prepared by Marjan Kluepfel, HGIC Information Specialist, and Bob Polomski, Extension Consumer Horticulturist, Clemson University. (New 04/02. Images added 04/09.)

HGIC 1067

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Hydrangea macrophylla, also called bigleaf or French hydrangea, has either pink or blue flowers. Flower color is determined indirectly by the soil pH, which affects the availability of aluminum in the soil. In acid soils the flowers will be blue, in alkaline soils the flowers will be pink. Aluminum is available to the plant in acid soils. Research has determined that the actual mechanism of color variation is due to the presence or absence of aluminum compounds in the flowers.

Blue Flower color of bigleaf hydrangea occurs in acidic soil
Blue flower color of bigleaf hydrangea (Hydrangea macrophylla) occurs in acidic soil.
Joey Williamson, ©2008 HGIC, Clemson Extension

For blue flowers, maintain a soil pH between 5 and 5.5. Apply aluminum sulfate or sulfur to reduce the pH to this range when you see new growth emerging in April. For application rates refer to the tables in fact sheet HGIC 1650, Changing the pH of Your Soil. Information on soil testing is available in fact sheet HGIC 1652, Soil Testing.

For pink flowers, maintain a soil pH of 6 or more by liming your soil. For more information on selecting a liming material and time of application refer to fact sheet HGIC 1650, Changing the pH of Your Soil.

Mature Height/Spread

Hydrangeas are deciduous shrubs that grow from 4 to 12 feet in height depending on the variety.

Growth habit of bigleaf hydrangea
Growth habit of bigleaf hydrangea (Hydrangea macrophylla).
Joey Williamson, ©2008 HGIC, Clemson Extension

Growth Rate

The growth rate is quite fast.

Landscape Use

Bigleaf hydrangeas are effective as single plants, massed or in containers on paved terraces.

Cultivation

Hydrangeas are easy to grow in well-drained soil, which should contain plenty of organic matter or humus. Bigleaf hydrangea prefers morning sun and afternoon shade. Avoid planting it in hot, dry, exposed sites. Most people buy hydrangeas when they are blooming, but spring or fall is the best time to set them out. For planting, dig a large hole approximately two feet across and one foot deep.

Bigleaf hydrangea responds to several light applications of fertilizer during the growing season. A general-purpose fertilizer, such as 10-10-10 applied at a rate of 2 cups per 100 square feet in March, May and July is suggested. It is not necessary to remove the mulch when fertilizing, but water soon after application to help dissolve the fertilizer and send it into the soil.

Bigleaf hydrangeas need ample moisture to prevent wilting
Bigleaf hydrangeas (Hydrangea macrophylla) need ample moisture and afternoon shade to prevent wilting.
Karen Russ, ©2008 HGIC, Clemson Extension

Hydrangeas have such big leaves that they can suffer if set out during hot weather. They need plenty of water, so plan to water thoroughly once per week or more frequently.

Bigleaf hydrangea should be pruned after flowering so they can develop "old wood" to form flower buds and to support blossoms the following summer. Avoid pruning after August 1.

One of the easiest ways to propagate bigleaf hydrangea is by layering. This is done by digging a trench near the plant and bending a section of limb down into the trench. Use a knife to remove a small ring of outer bark about an inch wide all the way around the limb. Then, cover the limb with soil, leaving 6 to 12 inches of the tip growth uncovered. Old established hydrangeas may also be divided in the early spring by using a shovel to divide the clump.

Problems

The most common reason for hydrangeas failing to bloom is winter injury. Other reasons may be too much shade, poor fertility and too much nitrogen fertilizer.

Hydrangeas are susceptible to Cercospora leaf spot, anthracnose and powdery mildew. For all three of these fungal leaf diseases, remove and dispose of fallen leaves.

Cercospora hydrangeae leaf spots with tan centers on bigleaf hydrangea.
Cercospora leaf spots (Cercospora hydrangea) with purple margins and tan centers on bigleaf hydrangea.
Joey Williamson, ©2014 HGIC, Clemson Extension

The larger necrotic (brown) areas are anthracnose caused by Colletotrichum gloeosporioides on bigleaf hydrangea.
The larger necrotic (brown) areas are anthracnose caused by Colletotrichum gloeosporioides on bigleaf hydrangea.
Joey Williamson, ©2014 HGIC, Clemson Extension

Powdery mildew can be controlled by sprays of 1% horticultural oil or thiophanate methyl every two weeks as needed. Examples of horticultural oils are Ferti-lome Horticultural Oil Spray, Southern Ag ParaFine Horticultural Oil, Bonide All Seasons Spray Oil, Lilly Miller Superior Type Spray Oil and Monterey Horticultural Oil. Examples of thiophanate methyl are Southern Ag Thiomyl Systemic Fungicide and Cleary’s 3336 Turf & Ornamental Fungicide.

Cercospora leaf spot can be controlled by sprays every two weeks with chlorothalonil, thiophanate methyl, mancozeb or myclobutanil. Examples of chlorothalonil are GardenTech Daconil Fungicide, Bonide Fungonil, Hi-Yield Vegetable Flower, Fruit & Ornamental Fungicide, Southern Ag Liquid Ornamental & Vegetable Fungicide and Ferti-lome Broad Spectrum Landscape & Garden Fungicide. Examples of mancozeb are Bonide Mancozeb Flowable and Southern Ag Dithane M-45. An example of myclobutanil is Spectracide Immunox. See under powdery mildew control for examples of thiophanate methyl.

Anthracnose can be controlled by sprays every two weeks with chlorothalonil or thiophanate methyl. See above for examples of products.

Insect pests on hydrangea include aphids, leaf tiers, rose chafers and red spiders.

Cultivars & Varieties

The cultivars of Hydrangea macrophylla are divided into two groups:

  • The "hortensias" have sterile flowers in solid masses, which are often so heavy they cause the stem to bend.
  • The "lacecaps" have a center of fertile, relatively non-showy flowers and an outer ring of showy, sterile flowers, which together form a pinwheel effect.

Hortensias:

  • 'All Summer Beauty,' 3 to 4 feet tall with flower heads produced on current season's growth, unlike other bigleaf hydrangeas.
  • 'Carmen', 4 feet tall with large pink flower heads.
  • 'Nikko Blue,' 4 to 6 feet tall with rich blue flower heads (in acid soil).
  • 'Blue Prince'
  • 'Compacta,' supposedly more compact than 'Nikko Blue' with darker green leaves.

Lacecaps:

  • 'Blue Wave,' 6 to 7 feet tall with lacecap flowers.
  • 'Coerulea,' perfect flowers a deep blue and ray flowers blue or white.

Several lacecaps feature silver-variegated foliage: 'Quadricolor,' 'Silver Variegated Mariesii,' and 'Variegata.'

Variegated foliage variety of bigleaf hydrangea
Variegated foliage variety of bigleaf hydrangea (Hydrangea macrophylla).
Joey Williamson, ©2008 HGIC, Clemson Extension

Climbing Hydrangea (Hydrangea anomala): This is a deciduous vine, which climbs high by clinging aerial rootlets. Leaves are roundish, 2 to 4 inches long. The white flower clusters are 6 to 10 inches wide in lacecap effect. Old plants have a peeling, cinnamon-colored bark.

Oakleaf Hydrangea (Hydrangea quercifolia): This deciduous shrub grows to 6 feet tall and has deeply lobed, oak-like, 8-inch leaves, which turn bronze in fall. The white flowers turn pinkish as they age.

'Snow Queen' has large white flower clusters. 'Snowflake' has a double-flowered appearance. 'Harmony' is a low-growing shrub, 3 feet tall and 6 feet wide, with spectacular 12-inch cones of sterile flowers.

A double-flowered oakleaf hydrangea
A double-flowered oakleaf hydrangea (Hydrangea quercifolia).
Joey Williamson, ©2008 HGIC, Clemson Extension

Oakleaf hydrangea fall color
Oakleaf hydrangea (Hydrangea quercifolia) fall color.
Karen Russ, ©2008 HGIC, Clemson Extension

Smooth or Snowhill Hydrangea (Hydrangea arborescens): This is a 5-foot-tall deciduous shrub with oval, grayish green, 4- to 8- inch leaves. Flowers are dull white and bloom late June through September.

Flowers of smooth hydrangea
Flowers of smooth hydrangea (Hydrangea arborescens).
Joey Williamson, ©2008 HGIC, Clemson Extension

'Annabelle' produces enormous (to 1 foot) globular clusters of sterile white flowers on a plant about 4 feet tall.

'Grandiflora' has 6-inch clusters on a similarly sized plant.

Peegee Hydrangea (Hydrangea paniculata): This is a 10- to 15-foot shrub or up to 25-foot tree. Leaves are 5 inches long and turn bronze in fall. Flowers are mainly fertile, in 10- to 15-inch clusters, white slowly fading to pink in fall. Peegee hydrangeas are tolerant of city conditions and grow well in seaside gardens. 'Tardiva ' flowers later, in August and September. 'Praecox' grows 10 to 15 feet tall and flowers in June.

Peegee hydrangea flowering in late summer
Peegee hydrangea (Hydrangea paniculata) flowering with white blooms in late summer.
Karen Russ, ©2008 HGIC, Clemson Extension

Hydrangea serrata is a small (to 5 feet tall) deciduous shrub similar to H. macrophylla but smaller, with smaller leaves and smaller flowers. 'Blue Billow' is only 3 feet tall.

Lacecap type flowers of Hydrangea serrata 'bluebird'
Lacecap type flowers of Hydrangea serrata 'Bluebird'
Joey Williamson, ©2008 HGIC, Clemson Extension

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