Hydrangea

China, Japan, Himalayas, Philippines, Indonesia, North and South America.

There are about 100 species of Hydrangea shrubs, small trees or vines, and most have two types of flowers present–fertile & sterile. Fertile flowers are small and inconspicuous, and are usually found near the center of a cluster. Sterile flowers are large and showy. Flowers are held in differing cluster formations.

Hydrangeas with round or dome-shape clusters of large, mostly sterile flowers hide fertile flowers are often referred to as mophead. Blue, pink, lavender, green, white & combinations of these colors are available. Mophead species include Hydrangea arborescens, Hydrangea macrophylla and Hydrangea serrata.

Hydrangeas with flat, round clusters of small, fertile flowers–edged by larger sterile flowers available in white, pink, lavender and blue–are referred to as lacecap. Lacecaps species include Hydrangea aspera, Hydrangea macrophylla and Hydrangea serrata, as well as the climbing Hydrangeas, H. anomala petiolaris, H. integrifolia & H. seemanii.

Hydrangeas with long, cone-shape clusters of white green or pink flowers are referred to as panicles or cones. Some are so full of big, sterile flowers that small fertile flowers disappear. Others are more open & have a lacy appearance. You can find cone flowers on Hydrangea paniculata and Hydrangea quercifolia.

Hydrangea leaves are deciduous or evergreen. Leaf form varies from simple, opposite or in whorls of three, oval or toothed, and smooth or serrated. Many Hydrangea varieties develop lovely red to dark purple & mahogany fall color. Peely bark adds winter interest to some species.

Blue & pink flowers of Bigleaf Hydrangeas, Hydrangea macrophylla change color depending on soil pH.

• Low pH is acidic = blue flowers
• Higher pH is more alkaline = pink flowers
• Mid-range pH = purple flowers

Soils west of the Cascades are typically acidic, so Hydrangeas are typically blue when planted in the ground. To turn flowers purple or pink, add lime to the planting area & reapply twice a year. To deepen the blue color, add Aluminum sulfate once a year. To maintain a specific pH, test the pH twice a year using a soil test kit. White hydrangea color cannot be manipulated with soil pH. Below, you’ll find target soil pH for specific colors.

• 4.5 deep, intense blue
• 5.0 medium blue
• 5.5 lavender-purple
• 6.0 pink-purple
• 6.5 mauve-pink
• 6.8 medium pink
• 7.0 intense, deep pink

Most Hydrangeas perform best when planted in dappled or afternoon shade. Those in full sun often burn and require extra watering.

Pee Gee Hydrangeas (H. paniculata), and Oak Leaf Hydrangeas (H. quercifolia) are exceptions that can be planted in sunny spots but will still perform well in part shade. Soil should be consistently moist and well-drained. Cold tolerance varies.

For blue flowers, use fertilizer for acid-loving plants. Use rose & flower food for all other hydrangeas. In all cases, follow the package directions for whatever food you choose.

Remove dead flowers in fall or late winter. Count 2 leaf-sets beneath the flower cluster and cut just above the second set. Repeat-blooming Hydrangeas can be dead-headed as old flowers fade.

Hydrangea arborescens blooms on new wood, so prune branches to knee-level in late winter.

To rejuvenate or down-size large Hydrangeas, take a long look at the overall structure of the plant in late winter. Make 3-5 thinning cuts evenly through the body of the plant, choosing the branches are the most offending and cut them back to a major branch or to the ground. After each cut, step back and choose the next wisely. Remove dead wood, and branches that are growing toward the interior of the plant. This type of careful pruning encourages growth in the interior & from the base during spring.

Next, remove dead flowers and cut back branch tips. Count 2 leaf nodes down from branch tips and cut above the second node. This ensures summer flowers.

Hydrangeas are prone to fungal problems, but they are typically not life-threatening. Leaf Spots and Powdery Mildew are the most common diseases in Portland, and they can often be avoided by increasing soil drainage and air circulation in the environment of the plant. If plants become diseased, remove affected foliage, remove all leaves from beneath the plant in fall when leaves drop naturally, and mulch the ground under the plant. Fungicides are available in addition to cultural treatment.

Succulent new growth attracts slugs, aphids and deer. All can distort and stunt growth. Slugs can be effectively controlled with bait or beer, aphids can be washed off with water or insecticidal soap, and there are several sprays out there that deter deer.