Identify your Hydrangeas

There are six main types of hydrangeas commonly grown in North American gardens.

Big-Leaf

Hydrangea Macrophylla
(also known as florist’s hydrangea, hortensia, mophead, or lacecap)

Hardy to USDA Zone 5

Proven Winners® varieties:

  • Abracadabra® series
  • Cityline® series
  • Edgy® series
  • Let’s Dance® series,
  • Paraplu™
  • Pink Shira™

Panicle

Hydrangea Paniculata
(also known as peegee hydrangea)

Hardy to USDA Zone 3

Proven Winners® varieties:

  • Bobo®
  • Fire Light™
  • Limelight
  • Little Lime™
  • Little Lamb
  • Pinky Winky®
  • Quick Fire®

Smooth

Hydrangea arborescens
(also known as Annabelle hydrangea)

Hardy to USDA Zone 3

Proven Winners® varieties:

  • Incrediball®
  • Invincibelle® Spirit
  • White Dome®

Climbing

Hydrangea petiolaris

Hardy to USDA Zone 4

Mountain

Hydrangea serrata

Hardy to USDA Zone 5

Proven Winners® varieties:

  • Tuff Stuff™
  • Tiny Tuff Stuff™

Oakleaf

Hydrangea quercifolia

Hardy to USDA Zone 5

Proven Winners® varieties:

  • Gatsby™ series

All hydrangeas have similar cultural needs, requiring:

  • Moist but well-drained soil (hydrangeas will not tolerate wet feet – ever!)
  • Some sun each day. Most people think of hydrangeas as shade plants, but they look and flower best with at least 4 hours of sun, ideally in the morning. Panicle hydrangeas are the most sun-tolerant and can take full sun in northern climates.
  • Plenty of water, especially as they are getting established. Hydrangeas have shallow roots, so they dry out quickly. A 2-3” thick layer of shredded bark mulch is a useful addition to any hydrangea planting.

It is the ways in which these six hydrangeas differ that make them confusing.

Flowering

The trickiest thing about hydrangeas is that different types have different flowering habits:

Panicle and smooth hydrangeas flower on new wood (growth created in the current season). Flower buds on these hydrangeas form after the plant leafs out in spring, and open a few months later in summer. As a result, these plants flower reliably each year, no matter how cold the winter was.

Bigleaf, mountain, oakleaf, and climbing hydrangeas flower on old wood (growth created in the previous season). Flower buds on these hydrangeas begin to form in late summer and must remain undisturbed all through the fall, winter, spring, in order to flower the following summer. As a result, these plants will not flower if:

  • They are pruned. Pruning at any time will remove potential flower buds.
  • They are browsed by deer, which will eat the flower buds.
  • They are damaged by weather. Winter weather isn’t actually the problem; rather, it is in spring, when several days of warm temperatures are followed by a sudden freeze, that flower buds are most likely to be damaged.

Reblooming hydrangeas, also known as remontant hydrangeas, are types of bigleaf and mountain hydrangeas that have the unique ability to flower on both old and new wood. Even if the buds are damaged in winter weather, the plant can still flower on wood it produces that season. Reblooming hydrangea varieties include the Let’s Dance series, and Tuff Stuff.

Color

All hydrangeas undergo some color change as their flowers age, but only big-leaf and mountain hydrangeas can change their color in a
predictable, controllable way.

It is not the pH of the soil that is responsible for this change – it is actually the presence of aluminum in the soil that does it.

  • Certain varieties of bigleaf hydrangeas cannot experience color change – generally speaking, the more intense the color, the less likely it can change (Cityline® Paris hydrangea is a good example). Similarly, white varieties of big-leaf hydrangea will not change color.
  • It is easier to change a hydrangea from pink to blue than from blue to pink, but both endeavors involve making chemical applications in specific amounts at specific times. A soil test is necessary to determine the next step.
  • Pennies or nails in the soil will not change the flower color!

Pruning

  • Avoid pruning reblooming hydrangeas and those that flower on old wood, altogether. Instead, site these hydrangeas appropriately so they do not need to be pruned, and choose varieties that do not get too big for their space.
  • New wood flowering hydrangeas can be pruned each early spring, just as the new growth begins to emerge. Remove up to one-third of the height each year if desired to encourage vigorous new growth and strong stems to support the flowers.
  • Hydrangeas do not strictly require regular pruning. They will grow and flower well with nothing more than the removal of spent flowers and any dead wood each early spring.

Hydrangea Fun Facts

  • There are about 49 species of hydrangeas. Four species are native to North America, including smooth hydrangea and oakleaf hydrangea.
  • Hydrangeas are notoriously water-needy, but the “hydra” part of their name actually refers to the seed capsules’ resemblance to ancient Greek water-carrying vessels.
  • Big-leaf hydrangeas and mountain hydrangeas are closely related and native to the same region of Japan, but mountain hydrangeas have better bud hardiness because they occur in the mountains where conditions are harsher.
  • A hydrangea flower consists of two different types of florets: the showy, papery flowers are known as sterile florets and serve only to attract pollinators; the tiny fertile florets are where pollination and seed-set take place. Mophead hydrangeas are comprised mostly of sterile florets; lacecaps mostly of fertile florets.
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