If you need a barren tree trunk or large chimney facade to be cloaked in a soft-looking foliage plant, consider using a climbing hydrangea vine. The woody stems bear interesting bark when the leaves drop away in fall and large flattened clusters of white flowers dot the vine like tiers in summer. There's no need to supply a trellis or wire form for these plants to grow upon; their aerial roots will fuse to the wall to facilitate their upward growth.
Two different species of garden plants carry the common name of "climbing hydrangea," both in the hydrangea family, Hydrangeaceae. The first is Hydrangea petiolaris, sometimes seen written with an older scientific name of Hydrangea anomala subsp. petiolaris. The second species is distinguished by usually being called the Japanese climbing hydrangea: Schizophragma hydrangeoides.
Both types of climbing hydrangeas hail from roughly the same native regions of eastern Asia. Hydrangea petiolaris grows naturally in the woodlands of Taiwan, Korea, Japan and the Russian peninsula of Sakhalin. Schizophragma hydrangeoides grows in the woodlands and on cliffs across Korea and Japan.
Hydrangea petiolaris grows 50 feet tall with woody stems that cling with aerial roots. The rounded dark green leaves have heart-shaped bases and may blush yellow in autumn before dropping away. In summer, this vine bears flat, 10-inch diameter clusters of white flowers. Small fertile flowers occur in the center of the cluster while the larger, showier and petaled sterile flowers form a ring around the cluster's edge.
Schizophragma hydrangeaoides grows to 40 feet in height, also with woody roots that clasp onto trees or rock faces. The long-stalked leaves have an oval shape with sharply toothed edges. In midsummer it bears wispy-looking, flattened, 8-inch diameter clusters of white flowers with a slight fragrance. Among the tiny flowers are larger, showier, white bracts shaped like teardrops.
Both species of climbing hydrangeas grow with similar needs. Plant either in a moist but well-draining soil rich in organic matter. They tolerate partial shade to full sun exposures, ranging from as little as four hours of sunlight to all-day sunlight in the garden. In general, Hydrangea petiolaris grows slightly better in non-alkaline soils (pH 7.5 and below) and is best in sheltered locations protected from wind.
Many gardeners plant either of these deciduous vines to be a rambling large ground cover or to climb up an exposed, sun-lit side of a tall tree trunk, tall house chimney or brick-wall facade. Plant the vines at least 24 inches away from the surface on which they eventually are to climb. The plants slowly establish and hasten their growth two to four years after their initial planting.
Hydrangea petiolaris grows and flowers better in colder regions with cooler summers, and is recommended for gardeners in USDA Hardiness Zones 4 through 9. In hotter, more humid summer zones, more shade is needed from afternoon sun for success. Conversely, Schizophragma hydrangeoides make a better choice in warmer climates in USDA Zones 6 through 9.