The hybridization of certain species of hydrangea has shifted them from their exclusive provenance in New England, the Pacific Northwest, and the more temperate areas of the South, to the flat gardens of the Midwest, where they are flourishing as both suburban and urban flowering shrubs. Along the way, these new cultivars of the panicle hydrangea (Hyrangea paniculata) acquired a greater cold hardiness, a tolerance to alkaline soils, and a preference for sunny conditions—ta-da, a perfect summer-blooming shrub for Chicago gardens.
There will always be the pink-and-blue envy directed toward the hybrids of the bigleaf hydrangea (Hydrangea macrophylla), whose full, sometime blue, sometimes pink, sometimes mauve flowers are coveted by gardeners who are led to believe that these new models can be persuaded to grow happily in the Midwest. The jury is still out on this issue, but the debate centers around whether the combo pink/blue plants are indeed hardy enough to handle an old-fashioned cold Chicago winter and still bloom the following spring, and whether a true-blue hydrangea can grow in our high pH soil without constant chemical amendments.
Smart gardeners should say hi and hi again to the H. paniculata hybrids, if they haven’t already done so. These are big plants, listed as growing between 8 and 15 feet, but easy to keep more in bounds with hard pruning in the spring—a good idea anyway since the plant flowers on new wood. They produce long panicle blossoms, 8 to 12 inches, quite impressive when the shrub is in full bloom, which it is for months. In fall, the blossoms begin to fade and dry to a silvery taupe tone at the same time fall color begins to dominate the landscape. These dried flower heads will remain on the shrubs well into winter, but they can be pruned off easily and brought inside for a lovely dried arrangement that might last longer than you really want it to as long as you keep the dried flowers out of water.
While gardeners might think of hydrangeas as typically shade lovers (true of the smooth hydrangea Hydrangea arborescens ‘Annabelle’ and ‘Grandiflora’, the panicle hydrangeas belong in the sun. Tolerant of our alkaline soils, they’re not happy if those soils dry out, and they’ll let you know their displeasure by wilting and yellowing foliage. Keep the soil evenly moist and mulch well to retain that moisture. Fertilizer is not necessary but a good helping of organic matter (compost, leaf mold) is appreciated in spring and again in late fall. No chemicals, no powdered amendments, no playing doctor with the soil.
Some of the original cultivars of H. paniculata (‘Grandiflora’, ‘Tardiva’, and ‘Unique’), boasted large white flower heads that remain upright in spite of their heaviness and size. A faint pink blush was observed on a few of the flowers but not enough to mark them clearly as pink-flowering shrubs. Their strong stems kept the dense blooms pointing skyward rather than flopping forever on the ground—an unfortunate habit of the smooth hydrangea hybrids. Subsequent introductions of panicle hydrangea featured flowers that opened white but morphed to pink or even deep rose before turning tan at the end of the season. ‘Interhydia’ (PINK DIAMOND) is one of the larger and better known of these types and can be seen at the Chicago Botanic Garden in the Rose Garden, the Sensory Garden, and massed along the Garden’s Wall. The late-to-bloom ‘Tardiva’ can be found on Evening Island; ‘Unique’ is planted around McGinley Pavilion.
Smaller (6 to 8 feet) choices include H. paniculata ‘Limelight’ whose fluffy white flowers turn chartreuse and then pink; or H. paniculata ‘Dvppinky’ (PINKY-WINKY) that gives the impression of two-toned flowers as the older blossoms turn to pink while the newer ones continue to emerge white. One of the newest offerings is H. paniculata ‘Bulk’ (Quick Fire™) whose claim to fame is that its white flowers bloom slightly earlier than the others before they turn deep rose. The Dwarf Conifer Garden has an attractive grouping of this showy variety interplanted with small conifer specimens, ornamental grasses, and ground covers.
As gardeners increase their appreciation for reliable, cold-hardy, long-flowering plants that easily adapt to northern or midwestern conditions, hybridizers will listen and continue to offer smart plants that satisfy our needs.