How Do I Know What Type of Hydrangea I Have?

Understanding the specific type of hydrangea you have is crucial for its optimal care and to anticipate its blooming characteristics. With a bewildering array of cultivars and species, differentiating between them can seem daunting. However, by focusing on key visual cues, bloom timing, and growth habits, you can confidently identify your hydrangea. This guide will walk you through the essential features to examine, empowering you to become a hydrangea identifier.

Table of Contents

The Blooms: A Primary Identifier

The most striking feature of any hydrangea is its flower. The shape, size, color, and arrangement of the blooms are significant indicators of the plant’s identity.

Mophead and Lacecap Flowers

Two of the most common hydrangea flower forms are the mophead and the lacecap.

Mophead Hydrangeas: These hydrangeas, primarily Hydrangea macrophylla, produce large, globe-shaped clusters of flowers. All the florets in a mophead are typically showy, sterile ray florets, creating a dense, ball-like appearance. Common examples include ‘Endless Summer’, ‘Nikko Blue’, and ‘Goliath’. The color of these mopheads can often change based on soil pH, ranging from vibrant blues in acidic soils to pinks and reds in alkaline soils. Whites generally remain white regardless of pH.
Lacecap Hydrangeas: Also predominantly Hydrangea macrophylla, lacecaps have a flatter, more delicate flower cluster. They consist of a ring of small, fertile inner florets surrounded by a single layer of larger, sterile outer florets. This arrangement resembles a delicate piece of lace. Popular lacecap varieties include ‘Twist n’ Shout’, ‘Bluebird’, and ‘Serrata’. The color-changing phenomenon is also present in many lacecap varieties.

Panicle and Oakleaf Flowers

Beyond the macrophylla types, other species boast distinct flower structures.

Panicle Hydrangeas (Hydrangea paniculata): These are easily distinguishable by their conical or pyramid-shaped flower clusters. The blooms are typically white or creamy in color when they first emerge and often mature to shades of pink, red, or burgundy as the season progresses. Unlike macrophylla hydrangeas, panicle hydrangeas bloom on new wood, making them reliably hardy in colder climates. Famous cultivars include ‘Limelight’, ‘Grandiflora’ (Peegee), and ‘Little Lime’. Their structure is generally more open and airy than the dense mopheads.
Oakleaf Hydrangeas (Hydrangea quercifolia): As their name suggests, oakleaf hydrangeas are characterized by their deeply lobed leaves, which resemble those of an oak tree. Their flower clusters are typically cone-shaped, similar to panicle hydrangeas, and are usually white, aging to a rosy pink or russet. The fall foliage of oakleaf hydrangeas is also a notable feature, often turning attractive shades of red, orange, and purple, adding significant seasonal interest. Cultivars like ‘Alice’, ‘Snow Queen’, and ‘Harmony’ showcase these traits.

Climbing Hydrangeas (Hydrangea anomala subsp. petiolaris)

Climbing hydrangeas are a category unto themselves, identified by their ability to ascend walls and structures. Their flowers are usually flat-topped clusters with a central ring of fertile florets and a surrounding ring of large, showy sterile florets, resembling a large lacecap. They have aerial rootlets that help them cling to surfaces. Their foliage is typically dark green and heart-shaped.

Leaf Shape and Texture: A Closer Examination

While flowers are the most obvious distinguishing feature, the leaves offer further clues to a hydrangea’s identity.

Hydrangea macrophylla Leaves

The leaves of Hydrangea macrophylla are typically ovate to elliptical, with serrated or toothed edges. They are generally glossy and dark green, though some varieties might have variegated or purplish foliage. The size of the leaves can vary, but they are usually quite substantial, contributing to the plant’s lush appearance.

Hydrangea paniculata Leaves

Hydrangea paniculata leaves are often coarser and more oval-shaped than those of macrophylla. They tend to be duller green and may feel slightly rougher to the touch. The leaf margins are usually less distinctly serrated.

Hydrangea quercifolia Leaves

The defining characteristic of Hydrangea quercifolia is its deeply lobed, oak-like leaves. These leaves are typically larger than those of other common hydrangeas and can be rough or fuzzy on the underside. Their significant contribution to fall color is a key identifying trait.

Hydrangea anomala subsp. petiolaris Leaves

Climbing hydrangeas have heart-shaped to ovate leaves that are glossy and dark green, similar to macrophylla, but they are usually smaller and more numerous, allowing them to create a dense cover on climbing surfaces.

Growth Habit and Structure: Understanding How They Grow

The way a hydrangea grows – its overall shape, size, and whether it blooms on old or new wood – provides vital diagnostic information.

Shrub Form vs. Climber

Shrub Hydrangeas: The vast majority of hydrangeas are shrubs. This includes Hydrangea macrophylla, Hydrangea paniculata, and Hydrangea quercifolia. They form rounded, bushy mounds that spread outwards. Their size can vary significantly depending on the species and cultivar, from compact bushes to large, sprawling specimens.
Climbing Hydrangeas: Hydrangea anomala subsp. petiolaris is the primary species grown for its climbing ability. It produces twining stems with adhesive aerial rootlets that allow it to attach to and ascend vertical surfaces like walls, trellises, or trees. Without support, it can also be grown as a dense groundcover.

Old Wood vs. New Wood Bloomers

This is a critical distinction for understanding bloom timing and pruning.

Old Wood Bloomers (Hydrangea macrophylla and Hydrangea serrata): These hydrangeas form their flower buds on the previous season’s growth (old wood). This means that severe pruning in the fall or winter can remove the buds for the following summer’s blooms. If you have a hydrangea that consistently produces flowers on established branches from the previous year, it is likely a macrophylla or serrata. If you are unsure, observe where the flower buds are forming.
New Wood Bloomers (Hydrangea paniculata and Hydrangea arborescens): These hydrangeas produce their flowers on the current season’s growth (new wood). This makes them much more forgiving with pruning. You can cut them back hard in late winter or early spring without sacrificing the blooms. If your hydrangea reliably blooms every year, even after significant pruning, it’s likely a panicle or smooth hydrangea.

Bloom Timing and Color Change: Subtle but Significant Clues

When your hydrangea blooms and whether its color shifts with the seasons can also help pinpoint its identity.

Bloom Time

Hydrangea macrophylla* and *serrata: Typically bloom from mid-summer to early fall. Their bloom time is dictated by the development of buds formed the previous year.
Hydrangea paniculata: Blooms from mid-summer through fall, with flowers often starting white and maturing to pinks and reds.
Hydrangea quercifolia: Blooms in early to mid-summer.
Hydrangea anomala subsp. petiolaris: Blooms in late spring to early summer.

Color Change (Reblooming vs. Non-Reblooming)

True Rebloomers (Hydrangea macrophylla and serrata): Many modern macrophylla and serrata cultivars are bred to be rebloomers. This means they produce flowers on both old and new wood, offering a more extended bloom season and greater reliability in colder climates where old wood might be damaged by frost. If your hydrangea consistently produces flowers throughout the summer, even after a hard prune, it might be a reblooming variety of macrophylla or serrata.
Color-Changing (Hydrangea macrophylla and serrata): The iconic blue and pink colors of macrophylla and serrata hydrangeas are directly influenced by soil pH. Acidic soils (low pH) favor aluminum uptake, producing blues, while alkaline soils (high pH) prevent aluminum uptake, resulting in pinks and reds. White varieties, like ‘Annabelle’ (Hydrangea arborescens), do not typically change color.
Color Development (Hydrangea paniculata): While paniculata hydrangeas do not change color based on soil pH, their flower heads do transition from white to shades of pink and red as they mature throughout the summer and fall. This is a developmental change, not a pH-dependent one.

Practical Steps for Identification

Observe the Blooms: What is the shape? Mophead, lacecap, cone, or flat-topped? What is the primary color, and does it change?
Examine the Leaves: Are they lobed like an oak? Are they glossy or dull? What is their shape and edge texture?
Assess the Growth Habit: Is it a shrub, or does it climb? How large does it typically get?
Note Bloom Timing: When does it flower each year?
Consider Pruning History: When do you typically prune, and has this affected its blooming? Does it bloom reliably on new growth or old?
Consult Resources: Use reliable gardening websites, plant identification apps, or local nursery experts. Compare your observations with images and descriptions of known hydrangea species and cultivars.

By systematically examining these characteristics, you can unravel the mystery of your hydrangea and ensure you are providing the best possible care for this beautiful and rewarding plant.