Hydrangeas: What is the Difference?

Hydrangea bushes are some of the most popular deciduous shrubs on the market today. They are valued for their beautiful large long-lasting flowers. They are relatively easy to grow and add so much to any landscaping theme. That said, we are asked over and over again: “Can you explain to me the differences among the hydrangeas?”; “Why aren't my bushes flowering?”, and “I want the flowers on my bushes to be blue...not pink or vice versa, and how do I do that?” This article will answer those questions, hopefully bringing you the results you want.

What are the differences in hydrangeas?

Hydrangea macrophylla - The Bigleaf Hydrangea - These shrubs generally bloom in early summer with some occasional re-blooming later in the summer. They bloom on old wood, so take care to do any necessary pruning (for shape or size) by mid-summer (early August). A good rule-of-thumb is to prune them back just as soon as the color has faded out of the flowers which is generally by mid to late July, and certainly NO LATER THAN early August. If they don't have sufficient time in late summer and early autumn to set flower buds for the following season, then all you will have next summer is a big, green bush! Bigleaf Hydrangeas are basically broken into 2 categories, Hydrangea macrophylla and Hydrangea serrata.

Hydrangea macrophylla Hydrangea macrophylla

Hydrangea serrata - a smaller bush than H. macrophylla with smaller leaves and flowers. Beautiful for the perennial border as it works well with other flowers. Lovely cultivars include 'Bluebird', 'Nigra' and 'Preziosa'. H. serrata also has a tendency for wonderful fall foliage coloration. In all other ways H. macrophylla and H. serrata are the same.
Hydrangea paniculata - The Panicle Hydrangea - These are generally large-flowered, late summer and early autumn blooming shrubs that are fairly large and fast growing. Most can be grown as either a large shrub or a small tree, and bloom on new wood. All benefit from a hard pruning either in the late fall or even better, in the early spring. All prefer full sun, and rich moist soil that drains well. Unlike other Hydrangeas, they tend to languish in partial shade.

Hydrangea paniculata Hydrangea paniculata

Hydrangea quercifolia - The Oakleaf Hydrangea - An outstanding shrub with multiple seasons of interest. The bare stems have papery bark that peels in sheaths reminiscent of cinnamon curls. The blooms are elongated, pyramidal and layered: very similar to a Tardiva Hydrangea. They appear in late June to early July and hold their creamy white color for several weeks before fading to pale green. The leaves are big, bold and reminiscent of an Oak tree. They are thick, leathery and dark green during the summer and turn to shades of maroon through dusky purple in the autumn, remaining effective into early winter. The foliage will have the most brilliant colors when the shrub is growing in full sun, but this beauty will also perform well in partial sun [3-4 hours]. Oakleaf Hydrangea requires rich, moist soil and will tolerate damp, heavy soil. Blooms occur on old wood, so take care to prune no later than late August if you expect any blooms for the following year. Grows to 5-6' tall and wide.
Hydrangea arborescens - The Smooth Hydrangea - 'Annabelle' is the most well known cultivar of the species. These hydrangeas are a great choice for a hedge, or as a specimen. Blooming from June through July, blooms begin a pale green and slowly turn to bright, pure white as they expand, then slowly turn green again as they age and finally turn pale tan in fall. The blooms are produced on the new wood and are anywhere from the size of a softball to a football. This shrub enjoys being cut back hard in fall (or early spring) and will thrill you when it grows back the following season. It grows 3.5 to 5 feet tall and tends to sucker and spread with age. This variety will tolerate some sun but does seem to prefer a partly shaded location, especially during the hottest summer months.

Hydrangea arborescens Hydrangea arborescens

Hydrangea anomala ssp 'Petiolaris' - This is the "Climbing Hydrangea". Climbing hydrangea are slow to become established, but with patience you will someday have a show stopper. New growth emerges in early May a brilliant, glossy spring green, and matures to a deep, dark green during the summer. The dome-shaped, lacy blooms are 5-8" diameter and are creamy white. They emerge in mid and late May for about 2 weeks, gradually turning a pale green. Even past bloom they remain effective most of the summer. In the autumn, the foliage turns a soft, buttery yellow before dropping. In the winter, you are left with a stunning network of gnarly, serpentine branches with bark like cinnamon that is very picturesque. This vine will cling to trees, brick, stonewalls and any other rough surface by using "pedicels". Pedicels are fibrous, sticky little "feet" the have the tenacious ability to grip any rough surface. Climbing hydrangea cannot twine around an object or grow up a smooth surface, so you will need to coax it up an arbor or solid fence using vine supports. Full sun to partial sun [4 hours] is best, and rich, moist, well-drained soil. Additionally, this Hydrangea is sweetly fragrant when in bloom!

Hydrangea anomala Hydrangea anomala

Why isn't my Hydrangea blooming?

If you (or a guilty spouse or an inexperienced landscaper) cut back hydrangea shrubs that bloom on old wood (macrophylla, serrata and quercifolia types only) too late in the summer or in the spring, you will be inadvertently be cutting off the dormant flower buds and may get few to no flowers at all the following summer. However, even if you do everything correctly, there is a SECOND reason that Hydrangeas may not bloom. Most supposedly "hardy" Hydrangeas are only "hardy" down to about 0 degrees Fahrenheit. If we have even one night during the winter where the temperature dips below that, the shrub is often killed partway back, and sometimes even all the way to the ground, including all of the flower buds. This rarely damages the plant, which simply regenerates from the ground-up, but you will miss the blooms the following season.

Why isn't my Hydrangea the color I want it to be?

Only certain varieties of Hydrangea macrophylla and serrata can have the color of their blooms altered. You may have wondered at the incredibly rich, almost violet-blue color that Hydrangeas assume at your favorite summer beach retreat. That color is achieved predominately because of the high levels of iron and aluminum in the sandy soil, and intensified by the acidity of the soil. To some extent, you can manipulate your hydrangeas to have the same effect by applying a once-a-year dose of aluminum-sulphate around the base of each shrub. Another trick is to acidify the soil by scattering coffee grounds around the base of the shrub during the winter months.