Panicle hydrangea

Identification and origin

Hydrangea paniculata belongs to the hydrangea family, Hydrangeaceae. It is native to eastern and southern China, Japan, Taiwan, Sakhalin Island, and the Kuril Islands. It has naturalized locally in the northeastern United States, Ontario, and Korea. The species name paniculata refers to the way the flowers are arranged in panicles.

It is a large, multi-stemmed deciduous shrub or small tree that grows quickly and has a coarse texture. In gardens it usually reaches 8–15 ft tall and can grow to 25 ft; it takes five to ten years to reach full size. It blooms most generously when kept at around 6–10 ft. It is grown as a multi-stemmed shrub or, less often, trained as a small single-trunk tree.

The leaves, opposite or sometimes in whorls of three at the branch tips, are oval, toothed, and 3–6 in long; they are dark green above, paler and slightly hairy beneath, and turn yellow before dropping in fall. The grayish-brown bark peels in strips on older wood.

From summer into fall it carries cone-shaped terminal panicles 6–8 in long. Each one combines small, creamy white fertile flowers with large, showy sterile flowers that range from white to pinkish. As they age, the clusters turn pink and then tan, and they stay ornamental all winter. They are good both as fresh cut flowers and dried. The fruits are small capsules of no interest to wildlife.

There are many cultivars: ‘Grandiflora’ (large creamy white flowers), ‘Limelight’ (lime green to creamy white flowers, more compact habit), ‘Little Lime’ (dwarf), ‘Phantom’ (creamy white flowers turning pink in fall), ‘Pinky Winky’ (two-tone panicles on purplish stems), ‘Tardiva’ (slender, late panicles), ‘Pink Diamond’, and ‘Bobo’, which stays around 3 ft.

Light

This is the hydrangea that handles sun best. The ideal spot gets morning sun and light afternoon shade, especially where summers are hot. It also thrives in full sun as long as the soil stays moist, and it still blooms in partial shade. It tolerates air pollution, salt spray, and urban conditions, and it does well facing any direction.

Watering

The roots are shallow, so the soil should stay evenly moist without ever becoming soggy, and the plant should never suffer from drought. Check the soil a little below the surface; when it is dry there, water deeply at the base rather than over the leaves. Young plantings, container plants, and shrubs in full sun are the most sensitive. Foliage that hangs limp at the end of the day is a warning sign, but always check the soil before watering, because roots damaged by too much water cause the same symptom. An organic mulch keeps the soil cool and moist and protects the roots.

Potting mix

It grows in clay, loam, or sandy soils, ideally rich in organic matter and well drained. It prefers neutral to acidic soil but also accepts chalky ground, which is best improved with organic matter. A light application of balanced fertilizer in early spring, late spring, and midsummer is enough.

Temperature

It is one of the most cold-hardy hydrangeas: it is grown in USDA zones 3a to 8b and comes through harsh winters without protection. It is a good substitute for bigleaf hydrangea in areas where that species is not winter hardy.

Repotting

It is mainly a shrub for planting in the ground, but it can be grown in a large container on a patio, especially compact cultivars such as ‘Little Lime’ or ‘Bobo’. Choose a wide container with drainage holes and a rich mix that holds moisture while draining well. When roots fill the container, move the plant to a larger one or replace the top layer of potting mix. In a container, watering needs more attention than in the ground.

Pruning

Because it blooms on new growth, it tolerates hard pruning. Prune in late winter or early spring, before the leaves emerge, so you can enjoy the dried flower heads all winter. Cut stems just above a plump bud or back to the branch collar, remove spent flowers, and take out a few branches to reduce the size or improve the shape.

An old, overgrown shrub can be renewed over three years: in spring, cut a third of the oldest stems to the ground the first year, half of the remaining old stems the second year, and the last ones the third year. The brittle stems bend under the weight of the flowers and are easily damaged by wind, so avoid very exposed sites. In winter, a wire fence about 2 ft tall protects young plants from rabbits.

Propagation

Cuttings are the usual method. Take softwood cuttings in early summer from flexible new shoots. You can also take hardwood cuttings in winter from mature stems. Seed is sown in spring in pots kept in a cold frame.

Common problems

• Aphids, scale, mites, plant bugs, nematodes, or vine weevils: they can show up but are rarely a serious problem. Check young shoots regularly.
• Leaf spot, powdery mildew, rust, gray mold: favored by wet foliage and poor air circulation; water at the base and thin out the branches.
• Bud blight, bacterial wilt, and, more rarely, honey fungus: remove affected parts.
• Broken branches: brittle stems weighed down by flowers or exposed to wind.
• Browsing: deer and rabbits can eat the shoots.

The same symptom can have several causes: before treating, look at the site, soil moisture, recent pruning, and the condition of the roots.

Toxicity

All parts are toxic to dogs, cats, and horses, and the plant is considered poisonous to people if eaten. The genus Hydrangea contains cyanogenic glycosides; eating the plant mostly causes vomiting, diarrhea, and lethargy, while cyanide poisoning is rare. The plant can also cause skin allergies, so wear gloves when pruning. If any part is swallowed, contact a veterinarian or a poison control center.