If I were to inquire which flowering shrubs could be used in the shade, I bet that 90 percent of the respondents would answer with Rhododendron. It would, in fact, be difficult to find an older home in Northeast Ohio that doesn’t have at least one Rhododendron and it is likely that the Rhododendron has never been pruned, thus appearing to eat the house.
Rhododendron maximum and R. catawbiense are the large-leaved and tall stalwarts of the genus that are hardy to zones 4 and 3, respectively. They grow so tall, however, that they are really not suitable for the perennial garden.
However, R. yakushimanum and its cultivars are dense, mounding evergreens that only grow three feet high and wide. The underside of the leaves has a woolly, bronze indentumum (fuzz) that shows when the wind blows. The buds are pink or red and the flower trusses are white or pink. These Rhododendron are hardy from –5 degrees to –15 degrees and rarely need any maintenance other than deadheading.
The evergreen nature of R. yakushimanum makes it an ideal component of the perennial garden in which most of the plants are herbaceous, i.e. they die back to the ground during the winter. The leathery texture of the leaves serves as an excellent foil for other foliar textures. The ideal location for R. yakushimanum is light to partial shade, out of strong winters sun and wind, which desiccates the foliage and can lead to an early death. Periodic watering is absolutely necessary since Rhododendron have shallow root systems. Assuming sufficient space, mass in groups of threes or intersperse single specimens periodically through the garden.
Hydrangea also have large leave but they, of course, are deciduous. To our great delight, the large panicles usually remain on the plant well into the winter, until strong winds blow them off. When I prune my Hydrangea in the spring, the panicles are frequently still present, The best Hydrangea in the spring, the perennial garden are H. arborescens ‘Annabelle’ (Annabelle Smoothleaf Hydrangea) and H. quercifolia. H. arborescens ‘Annabelle’ will grow three to five feet high and wide. Its stems seem strong until the buds become huge, round, white heads, at which time they pull the stems down and out like a fountain. Even pruning to the ground in early spring will not prevent this, so I recommend using grow-throughs, which should be placed over the plant as soon as you have pruned it back. ‘Annabelle’ will continue to bloom throughout the summer if it receives enough water. While she is a spectacular sight during the growing season, ‘Annabelle’ is a flowing white sculpture in the winter when covered with snow. A lovely vignette can be created by combining H. arborscens ‘Annabelle’ with a white-variegated Hosta such as ‘Cream and Sugar,’ a white-variegated ornamental grass for its fine texture such as Miscanthus sinensis ‘Variegats,’ and white-blooming Clematis with its divided foliage.
Another suitable Hydrangea for the perennial garden is H. quercifolia (Panicle Hydrangea). The species grows four to six feet high and slightly narrower and would be an excellent background plant with its large, oak-like foliage and large, pyramidal while panicles. During the winter, when the herbaceous plants have fallen over, the exfoliating bark will be quite visible. There are also two dwarf cultivars, ‘Peewee’ and ‘Sikes Dwarf,’ which only grow three feet and could thus be used in the middle of a border. No pruning is needed unless there is some dieback or you want to encourage a bushier form. These Hydrangea are more drought-tolerant than H. arborescens but the panicles will be larger and will last longer if water periodically. They provide an excellent backdrop for ferns or some of the hardy geraniums that like shade such as Geranium phaeum, G. nodosum or G. sylvaticum, all of which are woodland geraniumsand grow one and a half to three fee high and in a loose habit.
Keep in mind that H. macrophylla (Bigleaf Hydrangea) and H. serrata (Lacecap Hydrangea) will not flower well in a shady garden. These need at least a half-day of strong sun. There are infinite number of cultivars, with more coming, in these popular species. These Hydrangea need lots of water and wilt soon when sufficient water is lacking. The flowers range in color from white to pink to purple to blue, often dependent on the acidity of the soil – but not always.
The author, owner of Bobbie’s Green Thumb, is a landscape design consultant and lecturer. She can be reached at 216/752-9449.