In the dog days of late summer, when it seems that the only striking woody plants in flower may be an endless sea of fading Crape Myrtles, a gardener's eye is caught by the image of creamy white pyramids of blooms floating suspended above broad green leaves. These delightful floral crowns are not a mirage of summer's heat but the flower clusters of Hydrangea paniculata, the Panicle Hydrangea.
Panicle Hydrangea is a large shrub or small tree with rich green leaves that can reach anywhere from 10 to 20 feet in height with equal spread. A coarse, open habit is combined with somewhat loose, arching branching. Plants can be winter pruned as they mature to encourage tree form growth with a tidier habit if desired. This type of pruning has the added advantage of revealing the bark which can be quite beautiful on older shrubs as it matures to a ridged deep grey or brown. Since these plants bloom on new wood, they can also be cut to the ground each year and handled as 'woody herbaceous perennials' which Dr. J.C. Raulston, Arboretum Director, suggests where space is limited.
'Panicle' is the botanical term for the type of flowering structure which holds all of the individual blooms and creates the distinctive pyramidal cluster. Each cluster is made up of a combination of many small flowers which are fertile and not showy, as well as larger, showy flowers which are sterile. The proportion of showy sterile to non-showy fertile flowers will vary with cultivar and individual seedling plants. Flowers emerge a soft white which turns slightly pink as the flowers age and eventually dries to brown. The flower clusters are held on the plant through the fall, a characteristic considered wonderful for late season interest by some (but untidily unattractive by others!). Foliage offers little in the way of fall color.
Panicle Hydrangea is native to Asia and is one of the hardiest Hydrangeas available. It can be successfully grown throughout the southeast from the mountains to the coast. It prefers moist, rich, well-drained soils but has grown rapidly in Piedmont clay at The NCSU Arboretum (now the JC Raulston Arboretum). Full sun is best for the most prolific flowering but partial shade can also result in a good display.
There are a number of very worthy cultivars which can be propagated from spring softwood cuttings rooted under mist. Probably the most well-known cultivar is 'Grandiflora', the Pee Gee Hydrangea, whose flowers are all sterile and exceptionally showy. 'Grandiflora' flowers from early summer on. Its flower clusters can be extremely large and heavy, weighing the branches down to the ground after a rainstorm. (MORE) 'Floribunda' flowers later in the season and with many fewer sterile showy flowers than 'Grandiflora'( but still more than the species) in smaller clusters which gives a more subtle display. An especially vigorous and early flowering cultivar is 'Praecox' which blooms in June. 'Tardiva' (meaning 'late') on the other hand is significantly later than other Panicle Hydrangeas. Most years, 'Tardiva' does not begin blooming until September and it has a somewhat more upright habit than other cultivars. 'Unique' is a lovely form from England with mid-season flowering. Nestled in the Mixed Shrub Border at The NCSU Arboretum (now the JC Raulston Arboretum) a plant of 'Unique' illustrates this wonderful landscape use for Panicle Hydrangea while 'Tardiva' contributes beautiful white color and dimension to the Early-Late Border at the west end of the Perennial Border.
In the dog days of summer, the landscape itself seems to lie back and rest in the shade as few plants brave the heat at this time to flower boldly. Hydrangea paniculata, the Panicle Hydrangea, is an exceptional plant which offers a range of cultivars to bring beauty and variety to a late summer border's display.