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.
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.
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.
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 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.
The oakleaf hydrangea, or oak-leaved hydrangea is Hydrangea quercifolia. A number of cultivars exist and it is easily identified by its leaves.
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.
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.
Identify by Plant Characteristics
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.
- 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.
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.
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.
- If most of the older petioles are less than 1 inch long, the type is probably a macrophylla.
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.
- 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.
- 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.
- Learn why it is not flowering here: Why hydrangea Don’t Flower?
- Learn about common hydrangea myths: Hydrangea Myths
- Photo source for Hydrangea macrophylla; Swallowtail Garden Seeds