Hydrangeas Demystified

We've had such a beautiful stretch of weather lately, still summery but foreshadowing fall, and I feel renewed and refreshed enough to do some ambitious gardening again. This is a great time for planting perennials and flowering shrubs, the warm days and cooler nights perfect to encourage plants to root in and establish before the real fall weather arrives.

And there are many plants that save their biggest show for this time of year: Sedums, Asters, most of the ornamental grasses and many others. One of the most spectacular late-bloomers is Hydrangea paniculata 'Grandiflora', the "Peegee" Hydrangea (pictured above) an old-fashioned shrub that's often seen around local farmhouses. Its big pointed clusters of white flowers age to pink as the season progresses, and are often cut for dried flower arrangements. It's a classic, but there are lots more varieties that have been introduced since the "Peegee" came on the market just after the Civil War.

Hydrangeas are a large and varied group, native mainly to Eastern Asia and North America, and the many kinds seem to cause a lot of confusion among gardeners... in fact, they occasion some of the most frequently asked questions, such as "why won't my Hydrangea bloom?" and "what kind of Hydrangea do I have?"  In this post I'll attempt to clarify some of the confusion and show you just a little of the great variety in this really beautiful genus, a favorite of mine.

When explaining the differences in Hydrangeas, I like to break them down into four main groups for simplicity's sake:

The four main categories of Hydrangea for our Zone 5 area are (clockwise from upper left) Oakleaf Hydrangea (Hydrangea quercifolia), Smooth Hydrangea (Hydrangea arborescens), Panicle Hydrangea (Hydrangea paniculata), and Mophead Hydrangea (Hydrangea macrophylla).


Let's start with the most distinctive and least confusing: the American native Oakleaf Hydrangea, Hydrangea quercifolia. This beauty is found in woodlands all through the southeastern states, but will grow well in our area although a really harsh winter will sometimes knock it back to the snowline. However, it quickly regrows from undamaged portions and will even begin to sucker at the root, forming a well-mannered colony in time.

What makes this Hydrangea so distinctive is the beautifully shaped foliage, recognizable enough for even a child to identify, that turns gorgeous shades of gold, orange, scarlet and wine red in fall. The bark is interestingly shaggy also, and the fuzzy buds are cute. It flowers in mid- to late summer, the long panicles turning pinkish-red in some cultivars (like 'Ruby Slippers') or just a pleasant shade of blush or tan in the straight species.

One of the very best native shrubs, with only one caveat:  the deer relish the fuzzy buds in winter, so grow in a protected area or net it until it grows above the browse line, usually four or five feet. Oakleaf Hydrangeas need very little pruning, just a shaping from time to time, removal of dead branches and cleaning up last season's tattered flowers in late winter or early spring.

Next comes another tough American native, the Smooth Hydrangea, Hydrangea arborescens. Most people are familiar with this in one of its cultivar forms, the large-flowered 'Annabelle' (left above), but there are several lovely varieties in commerce as well as the straight species. 'Incrediball' (awful name) has flowers even larger than 'Annabelle' and 'Invincibelle Spirit' (right above) is a pretty soft pink version. These types will grow and flower well in full sun, but I think they're best when given high dappled shade from tall trees or only morning sun, as hot afternoon sun tends to make them wilt and look a bit tired.

For a more naturalistic look, there are lacecap versions too, like 'Haas Halo' (top above) and 'White Dome' (bottom above). I love these for their cool summer flowers and especially for their ability to hold snowfall in the winter. All the arborescens types can be cut almost to the ground in the spring if you want the largest flowers (but fewer of them), or pruned back by one third for smaller but more numerous flowers. They bloom on the current year's growth.

Equally tough and hardy, though not native, are all the Panicle Hydrangeas, Hydrangea paniculata cultivars, including the well-known "Peegee" that I mentioned at the beginning of this post. These are some of the most reliable shrubs for our area, and come in many beautiful varieties... some of the best are 'Limelight', which opens a cool greenish-white and ages to pink, 'Phantom' (above) boasting enormous flower clusters, 'Quickfire' and 'Pink Diamond', with open panicles that color up fast to deep rose pink, 'Unique', another one with large lacy flowers, the late-blooming 'Tardiva' and many others. All these are large shrubs, eventually 8-12 feet tall, but there are dwarf varieties available too, like 'Little Lamb' and 'Bobo', to fit into a smaller planting scheme.

Very often nursery customers will ask for a "Tree Hydrangea", but really, there's no such thing. What they're looking for is a paniculata type that's been trained into what's properly called a standard, a horticultural form that looks like a small tree, with a rounded head on top of a slender "trunk". Best used in very formal settings, these are elegant when well placed but can sometimes topple and break in winter storms, in which case they will regrow from the root in the plant's natural form, a multi-stemmed shrub. All the Hydrangea paniculata varieties flower best in full sun, and bloom on the current season's growth, so they should be pruned in early spring before they leaf out, and can be pruned hard (down to half the size) or moderately (removing 1/3 the size of the shrub).

Panicle Hydrangeas can make dramatic landscape statements. This is 'Limelight'.

Last of the four groups is the one that seems to cause the most consternation, at least in our Zone 5 climate:  the Mophead Hydrangea, Hydrangea macrophylla. These are the gorgeous blue Hydrangeas that are such a feature of Nantucket, Cape Cod and Long Island, and southward all the way to the Gulf Coast. They are also hugely popular in Europe, where they are known as Hortensias, and were hybridized in hundreds of beautiful varieties in the 19th and early 20th centuries. The sad truth is that these romantic beauties are not well suited to our winter climate, because they set their flower buds a year ahead and must winter them over to bloom well. The plants will survive, but not the flower buds, so flowering is typically sparse, often only below the snow line, but they're sold in every big box nursery and grocery store, leading to much confusion about their hardiness.

Recently, some varieties have been developed that flower on the current year's growth, like 'Endless Summer' (blue, above), 'Blushing Bride' (white flushed pale pink), 'Twist-n-Shout' (pink or blue lacecap, left below), and 'Diva' (very large pink lacecap, right below). The jury's still out on these in our area, as they've only been on the market a few years, but some local gardeners report success, and if you must have a blue Hydrangea these are the only ones to consider here in the Hudson Valley.

There's also quite a bit of mythology about changing the color of these Hydrangeas from pink to blue or vice versa... the pH of the soil and the presence or absence of aluminum in the soil is determinative, but adding pennies, nails, aluminum foil or coffee grounds will not do the trick! Mopheads have glossy, smooth leaves and appreciate shade from the hottest sun and reliable moisture. Pruning should be done in spring, but sparingly and only to remove spent flowers and tips that have winter-killed.

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There's one more type of Hydrangea I want to mention, because it's such a beautiful plant, well suited to our area and can't be confused with the four groups above... that is, the Climbing Hydrangea, Hydrangea petiolaris  (shown above at the much beloved local garden of Hudson Bush Farm). This requires patience and a very sturdy pergola, fence or masonry wall for support, because once it's established and really starts growing it can become quite a lovely monster. Although slow to settle in, it isn't too picky about soil and tolerates quite a bit of sun. It can be used to perfection spilling over an old stone wall.


That's my little tutorial, and I hope it's clarified some questions for you. Hydrangeas are so varied that some confusion is inevitable, but don't let that stop you from growing and experimenting with these handsome plants, so many of which will do well here in our region. A competent nursery will always be happy to guide you in your selection and help you find the variety that suits your property best, whether it's a farmhouse, townhouse, mansion or suburban ranch!