Hydrangea how-tos for 3 categories — and for big, beautiful blooms

ONE QUESTION OFTEN put to me as a plant “expert” (their word, not mine) is, “Why won’t my hydrangea bloom?” My answer is always the same: It depends.

Whether producing fulsome globes, starry blossoms (sometimes referred to as “lacecap”) or bold cones, a properly managed hydrangea will bloom for months on end. Hydrangeas flourish in full sun to part shade and appreciate regular water during the dry season. Generally, the more sun a plant receives, the more water it will require.

Garden care (specifically, pruning) depends on which hydrangea species you’re growing. More precisely, you need to know whether your plant blooms on “old wood” or “new wood.” That is, are flower buds formed on last year’s (older) limbs, or at the tips of the current season’s (new) growth? Fun fact: The tiny budlike flowers on lacecap blooms are fertile and loved by pollinators, while the larger, more showy florets are sterile.

It all can get a bit confusing, but simply speaking, hydrangeas fall into one of three categories. Fortunately, the tag that came with your plant is your guide to bountiful blooms.

Smooth or panicle hydrangeas (H. arborescens or H. paniculata) produce upright cone-shaped blooms in white, tinged with green, or blushed with pink. Blossoms are produced on new wood, so it’s safe to prune plants in late winter or very early spring. This category of hydrangea tolerates and even thrives with more sun but might take several years to establish and begin blooming. Mulch helps to retain soil moisture and encourages the plants to settle in. Some varieties, like the popular ‘Limelight’, grow 6 to 8 feet tall and wide, although recent breeding has produced smaller cultivars, including Little Lime®, that are much more compact. As temperatures cool in fall, the blossoms ripen to a lovely antique rose.

Bigleaf or mountain hydrangeas (H. macrophylla or H. serrata) produce the iconic mophead or starry blooms that most gardeners associate with this popular summer-blooming shrub. Both bigleaf and mountain hydrangeas bloom on old wood. A misplaced clip at the wrong time of year, and you can say goodbye to this year’s blossoms. Smaller dwarf varieties, some even suitable for containers, don’t require any pruning. But, if you must prune, do so in summer, while the plant is still actively producing new wood.

Flower colors vary from deep cornflower blue to shocking pink, or a softer blue to delicate pink, depending on how acid the soil is. Your local nursery will be able to point you toward the appropriate amendment if you’re looking to strengthen the blue on your plants, although hydrangeas that are bred with pink flowers will never turn true blue. The blooms age gracefully, turning shades of deep rose, violet and wine at the end of the summer, and hold their colors beautifully as a late-season cut flower.

Climbing and oakleaf hydrangeas (H. anomela petiolaris and H. quercifolia) differ from other hydrangeas both in habit and form. Climbing hydrangea produces large creamy lacecap blooms. Arial roots allow plants to adhere to their support. Growth, and blooming, gets off to a slow start but accelerates over time, with stems reaching to 50 feet or more. You’ll find beautiful examples of climbing hydrangeas on towering conifers in gardens around our region.

While most gardeners prioritize hydrangea flowers over the plant’s foliage or form, the oakleaf hydrangea, native to the southeastern United States, is one of the most striking garden shrubs of any sort with nearly year-round interest. Creamy white cone-shaped flower clusters form on old wood and are set off by deep green, lobed oaklike foliage. Ripening blossoms fade to rose and deep wine. In fall, the leathery foliage turns vivid shades of purple and bronze and holds through early winter before dropping to reveal attractive cinnamon-brown peeling bark. It might take a few growing seasons for oakleaf hydrangea to begin flowering, but its beauty is apparent immediately.