Hydrangea Identification

Robert Pavlis

Are you wondering why your hydrangea is not flowering? Would you like to know when and how to prune your hydrangea? These are important questions, but no one can provide the correct answers until you know what type of hydrangea you have. This post will help with your hydrangea identification. It won’t provide cultivar names but it will identify the type of hydrangea.

It is always a good idea to keep plant names since it makes it so much easier to find the correct cultural information at a later date. But life happens and it is quite common for people to lose the name of a plant.

Hydrangea macrophylla blue bigleaf hydrangea, Hydrangea Identification
Hydrangea macrophylla also called the bigleaf hydrangea

Hydrangea Types

There are several types of hydrangea and they don’t all take the same growing conditions. The type is based on the plant genetics – what species was used to develop the plant. Here is a brief list of the types that will be discussed in this post.

Macrophylla (Bigleaf) Type

Macrophylla hydrangea have been bred using mostly Hydrangea macrophylla and Hydrangea serrata. Its common names include bigleaf hydrangea, French hydrangea, lacecap hydrangea and mophead hydrangea. In warmer climates where it does well, this is a very popular hydrangea because of its blue flowers. It also produces white, pink and purple flowers. The term macrophylla means large or long-leafed.

Plant Science for Gardeners by Robert Pavlis

Arborescens (Smooth) Type

The smooth type has been bred using Hydrangea arborescens. It is commonly called smooth hydrangea, snowball hydrangea or Annabelle hydrangea. The term snowball comes from the fact that this type has the largest white snowball like flower heads. The other common name, Annabelle, really should not be used since it confuses people into thinking all smooth hydrangeas are Annabelles – they are not. Annabelle is the cultivar name for a specific Hydrangea arborescens and the name should only be used when referring to it.

Hydrangea arborescens (smooth hydrangea), by Robert Pavlis, Hydrangea Identification
Hydrangea arborescens (smooth hydrangea), by Robert Pavlis

Paniculata Type

This group of plants has Hydrangea paniculata in its genes. The common name, panicled hydrangea, refers to the shape of the flower head. Instead of being round it is cone shaped.

Historically, the most popular cultivar in this group is called Hydrangea paniculata ‘Grandiflora’. The name was shortened to PG hydrangea, using the first letters of paniculata and grandiflora. This plant became so popular that some people incorrectly refer to all paniculata types as PG hydrangeas. This leads to a lot of confusion. A plant that is is labeled as PG may or may not be Grandiflora. You never know what you are getting with a PG.

Hydrangea paniculata 'limelight', by Robert Pavlis, Hydrangea Identification
Hydrangea paniculata ‘limelight’, by Robert Pavlis

Climbing Type

Hydrangea petiolaris and Hydrangea anomala are very similar species, that are known as the climbing hydrangeas. H. petiolaris is much more popular in the garden than H. anomala.

Oakleaf Type

The oakleaf hydrangea, or oak-leaved hydrangea is Hydrangea quercifolia. A number of cultivars exist and it is easily identified by its leaves.

Hydrangea quercifolia, the oakleaf hydrangea, by Robert Pavlis, Hydrangea Identification
Hydrangea quercifolia, the oakleaf hydrangea, by Robert Pavlis

Hydrangea Identification

The following Hydrangea Identification Process has been split into two sections. The first section (green section) has been designed so that you can identify an hydrangea without knowing anything about its flowers. This is very useful if you are trying to figure out why your plant is not flowering.

Building Natural Ponds book, by Robert Pavlis

The second section (blue section) works through a process of identification using flowers. You can use this section to confirm the ID you made in the first section.

Start with the section called “Identify by Plant Characteristics”. Work your way through this section until you get an ID. Then skip the rest of the section.

If you know what the flowers look like, have a look at the section called “Identify by Flower Characteristics” and confirm your ID.

The following process works most of the time. In the plant world there are always exceptions but it is unlikely that your plant is one of them. If you do have an exception, let me know about it in the comments.

YouTube video

Identify by Plant Characteristics

Growth Habit

Hydrangeas have three different growth habits.

  • If the plant is climbing, it will be a climbing hydrangea – this one is easy.
  • If the hydrangea is a tree with a single trunk, the plant is a paniculata type.
  • If the plant is a shrub, move on to Leaf Shape.

Leaf Shape

  • If the leaf has an oak shape as pictured below, it is oakleaf type.
  • If the leaf is not an oak shape, move on to the Number of Leaves Per Node.
Oakleaf hydrangea, by Robert Pavlis, Hydrangea Identification
Oakleaf hydrangea, by Robert Pavlis

Number of Leaves per Node

A node is the point on the stem where one or more leaves are attached. Have a look at the older, larger leaves on the stem since the newer small leaves at the tip of stems grow differently. Look at all the stems since the number of leaves can vary from stem to stem. Young paniculatas and poorly grown ones may not have 3 leaves.

  • If at least one node on the plant has 3 leaves coming out, it is a paniculata type.
  • If none of the nodes have 3 leaves, then move to Petiole Length.
Node with 3 leaves, looking down the stem, Hydrangea paniculata, by Robert Pavlis, Hydrangea Identification
Node with 3 leaves, looking down the stem, Hydrangea paniculata, by Robert Pavlis

Petiole Length

A petiole is the short stem that connects the leaf to the main stem. Check the length of the petiole on some of the older leaves. Ignore the smaller leaves at the tip of the branch since the petiole there is still growing.

  • If most of the older petioles are more than 1 inch long, the type is probably arborescens.
Hydrangea arborescens showing long petioles, by Robert Pavlis, Hydrangea Identification
Hydrangea arborescens showing long petioles, by Robert Pavlis
  • If most of the older petioles are less than 1 inch long, the type is probably a macrophylla.
Hydrangea macrophylla showing short petioles, by Robert Pavlis, Hydrangea Identification
Hydrangea macrophylla showing short petioles, by Robert Pavlis

Identify by Flowers Characteristics

Climbing hydrangea and oakleaf hydrangea are easily identified by the above plant characteristics so this section will not include them.

Shape of the Flower Head

  • If the flower head is cone shaped it is probably a paniculata type.
Hydrangea paniculata with cone shaped flower head, by Robert Pavlis, Hydrangea Identification
Hydrangea paniculata with cone shaped flower head, by Robert Pavlis
  • If the flower head forms a round ball or a flat disk then it is either a macrophylla or arborescens type. Go to the Flower Color section.
Hydrangea arborescens showing dome shaped flower head, by Robert Pavlis, Hydrangea Identification
Hydrangea arborescens viewed from the side showing the dome shaped flower head, by Robert Pavlis

Flower Color

  • If the flower color of newly opened flowers is either blue, purple or pink then you have a macrophylla type.
  • If the flower buds open a green color, then turn white, and as they age turn green or greenish brown, you have an arborescens type.
  • If the flowers open white and stay white until they get old, then you probably have a macrophylla type. White flowering macrophylla types are less common, but they do exist.

note: new breeding is starting to produce some arborescens that have a pink tinge in the flowers, eg ‘Eco Pink Puff’. You can expect this pink to get stronger in future cultivars.

I Know The Type – Now What?

Now that you know the type of hydrangea you have you can find out more about your plant.

  1. Learn why it is not flowering here: Why hydrangea Don’t Flower?
  2. Learn about common hydrangea myths: Hydrangea Myths

 

References:

  1. Photo source for Hydrangea macrophylla; Swallowtail Garden Seeds

 

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Robert Pavlis

I have been gardening my whole life and have a science background. Besides writing and speaking about gardening, I own and operate a 6 acre private garden called Aspen Grove Gardens which now has over 3,000 perennials, grasses, shrubs and trees. Yes--I am a plantaholic!

31 thoughts on “Hydrangea Identification”

  1. Hi, thanks so much for your identification guide. I “inherited” hydrangeas at my new home which bloomed beautifully during the summer. According to your tool I seem to have H. arborescens except that my blooms are light purple (if I recall correctly they started out green). Are some arborescens cultivars purple?
    I’m in Zone 7 and the recent onset of colder temps have caused the leaves to blacken and die. I’m very tempted to prune them down now. Will that harm the growth/flowering next year?

    Reply
  2. I have four Macrophylla hydranga plants along my driveway. We hae had the for about 5 years. The first year they bloomed a lovely Blue color. Each year I feed them the hydranga fod recommended to make them turn blue. I only get a hot pink bloom. Why are they not turning blue even when I feed them the proper food?

    Reply
  3. My hydrangea was named Flopsy Mopsy…..it has lots of small, round pink blooms that hang. It is full of dead looking branches….not sure if I should prune some out this winter ?? Does it bloom on old or new wood? Thank you……

    Reply
  4. Great Info! I think I have macrophillia hydrangea, pink, Missouri Gardner, not having luck with blooming. East side, 4 hours 10am- 3 pm sun,
    beautiful full plants , 7 years old ,one or two blooms a year. Do I need to prune to get to bloom?

    Reply
  5. Excellent explanation. Thank you.
    I had two macrophylla (blue flowers) and two arborescent , blooming steady for 8 years (zone 5). When we moved to northeastern Ontario (zone 3), 6 years ago, I took my bushes with me.
    The macrophylla never flowered again; having just lush green leaves. That’s O.K. I did assume it’s because of long cold winters.
    The other two (arborescent) continue to flower each year.
    Both variety grow in the same soil and location.

    Reply

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