Hydrangeas are popular shrubs with showy flower heads in hues of blue, white, or pink in summer or autumn. Many gardeners are surprised to find out that not all hydrangeas are shrubs–there are a few climbing species that make first-rate vines.
- Common name: Hydrangea
- Botanical name: Hydrangea spp.
- Zones: 4 to 10, depending on species
- Size: To 50 feet tall and 12 feet wide, depending on species
- From: Areas of Asia and North and South America
- Family: Hydrangeaceae (hydrangea family)
- Sun: Full sun or partial shade, depending on type
- Soil: Moist, well-drained, and rich in organic matter
- Moisture: Water during times of drought.
- Mulch: Put a 2- to 3-inch layer of mulch over the soil around the plants. Avoid laying mulch directly against their stems-leave a gap of several-inches.
- Pruning: If necessary, prune H. arborescens, H. paniculata, and H. quercifolia in late autumn or early spring. Prune H. macrophylla immediately after flowering to keep from cutting off developing flower buds.
- Fertiliser: In good soils, fertiliser isn’t necessary. In other soils, use a timed-release product in spring.
- Cuttings: Take cuttings in early or midsummer.
- Aphids: These small insects often appear in large numbers on a plant’s new growth. Spray aphids off daily with a stream of water; they will not bother plants after being knocked to the ground. Use an insecticidal soap or neem-oil spray if infestations are severe.
- Gray mold: Gray mold starts as a leaf spot and may develop into fuzzy gray areas on the plant. To deter this and other fungal diseases, avoid getting the foliage wet, and thin the plants to provide better airflow.
- Leaf spot: In summer or autumn, leaves develop yellow or brown spots, often with concentric rings that form a bull’s-eye pattern. To deter it, prune the plant for good airflow and avoid wetting the foliage in afternoons and evenings.
- Powdery mildew: This disease tends to appear in mid- to late summer. Infected leaves become covered with a gray powder and drop off. To deter the disease, prune the plant to keep good air circulation and avoid wetting the foliage in afternoons and evenings.
- Rust: In summer, rust creates leaf spots and small masses of rusty-colored powder on leaves. Infected leaves die by the end of the season. To deter it, avoid getting the foliage wet; make sure there’s good air circulation around plants.
- Scale: Scale insects crawl up plant stems and cling to the plant. They appear as small, raised spots and are easy to overlook. To deter scales, encourage beneficial insects and apply insecticidal soap or horticultural oil.
- Slugs and snails: Slugs and snails chew leaves at night and leave slimy trails. To deter them, surround plants with a ring of horticultural grade diatomaceous earth or slug bait. Some gardeners have had success with barriers of copper strips around plants. If slugs aren’t particularly numerous, set out shallow containers of beer at ground level. Slugs are attracted to the yeast, and crawl into the liquid and drown.
- H. macrophylla cultivars are sensitive to soil pH and show it in their flower color. In alkaline soils, the flowers have pinkish tones (even in blue-flowering cultivars). In acidic soils, the flowers gain bluish tones. However, if you have a pink-flowering cultivar, it will never have true blue flowers no matter what the soil pH is. Likewise, a blue-flowering hydrangea will never have clear pink blooms.
- Before adjusting your soil pH to modify the flower color, always take a soil test. Certain nutrients are available to plants only at certain pH levels, so you could starve your plants if you change the pH too drastically. Also, plants have limited pH ranges they can tolerate. If you change the soil past this range, the plants will die.
- Hydrangea arborescens: Grows to 5 feet. Blooms in summer with white flowers. Zones 4 to 9. Native to North America.
- Hydrangea macrophylla: Known as the florists’ hydrangea, it grows to about 6 feet. Blooms in shades of pink, blue, and white. Zones 6 to 9.
- Hydrangea paniculata: Grows 10 to 22 feet and has white flower heads summer and early autumn. Zones 4 to 8.
- Hydrangea petiolaris: Vine that climbs to 50 feet. Bears white flower heads in summer. Zones 4 to 9.
- Hydrangea quercifolia: Oakleaf hydrangeas grow about 6 feet tall and have white flower heads from midsummer to autumn. The foliage often turns purplish in autumn. Zones 5 to 9.
- H. serrata: Grows to 4 feet. Wide with blue or pink lacecap flowers in summer and autumn. Zones 6 to 9.