Hydrangea – Blooming, Growing, Pruning

(Question)

Having several issues with my hydrangeas .
One was planted 2 years ago, has grown well with very healthy looking foliage but has never bloomed
Another planted at the same time in the same bed will not grow. This bed is west facing but has partial shade from the house and tree
Still another planted last year and flowered then did not flower this year, no pruning done, in a different bed that is east facing with clay soil(amended with lots of compost)
What am I doing wrong?

(Answer)

Many Toronto gardeners have had problems with their hydrangeas this year, some of which undoubtedly stem from last winter’s harsh conditions.  We’ve received many questions that are similar to yours.  Some hydrangea varieties that bloom on old wood do not require pruning, but those that bloom on new wood should be pruned in order to flower.  So the first question is: what different varieties of hydrangea do you have?

Here are some thoughts that I have pulled together from other Toronto Master Gardener ASK posts, which I hope will help:

  • If you have an oak-leaf hydrangea (Hydrangea quercifolia) which has not bloomed:

Many species of hydrangea have been blooming prolifically this year in Toronto, which is a wonderful sight.  So why doesn’t your oak-leaf hydrangea (Hydrangea quercifolia) have any blooms?  You are not alone, my own oak-leaf hydrangeas have not bloomed this season.

The reason is most likely weather related.  You can probably blame it on the prolonged cold weather we endured last winter.  The blooms on Hydrangea quercifolia form on old wood (last summer’s growth).  Since oak-leaf hydrangeas are actually native to S.E. North America, where winters are generally milder, the buds that were formed last year were, no doubt, killed by our frigid arctic temperatures.  Your hydrangea may also have suffered some die-back of branches, which would have been pruned back to the ground or to emerging leaves this spring.

Unlike other hydrangeas which bloom on new wood, oak-leaf hydrangeas generally do not need to be pruned except to limit their size or direct the shape.  When necessary, branches can be pruned back half-way as the flowers fade.  Assuming that you did not prune your plant last year or this spring, the buds simply froze and therefore could not produce any flowers.  If we have a more temperate winter this year, you can look forward to your plant blooming next summer.

  • If you know which species of hydrangea you have, but are uncertain of their characteristics:

There are many species of Hydrangeas but they can be divided into two large groups, those that bloom on old wood and those that bloom on new wood.

The following is a list of the more common species and whether they bloom on old or new wood:

Species Cultivars Common name

New wood

Old wood

H. aborescens Annabelle

X

H. macrophyllas* Mophead

X

H. macrophyllas normalis Lacecap

X

H. paniculata PeeGee

X

H. quercifolia Oakleaf

X

* recently new H. macrophylla cultivars have been developed that bloom on old and new wood, like the Endless Summer Series and Let’s Dance Series.

Hydrangeas that bloom on new wood are a more reliable bloomer.  You can cut them back to the ground either in the fall or spring and they will bloom in the summer.

  • A lot of confusion exists around when and how hydrangeas can be pruned but once a hydrangea is correctly identified, pruning becomes fairly easy.

The nickname mopheads (H. macrophylla) is descriptive of the shape of their blooms. Blue, pink and purple are the most common colours. White is fairly uncommon. If the blooms on your hydrangeas are white, consider the possibility that they are not macrophyllas but are one of the other species.

Mophead hydrangeas do not have to be pruned back unless they are very old. Removing dead stems and blooms is the only pruning that should be done for the health of the plant, and these can be removed at any time. But if your hydrangea is getting much too large or old, use the following method.

These hydrangeas bloom on old wood. (Stems that have been on the hydrangea since the summer before the current season.) They produce flower buds in August, September or October for the following summer’s blooms. If those stems are pruned in the fall, winter, or spring, the bloom buds will be removed, and there may be little or no bloom the following summer (usually June/July for the northern hemisphere).

Unfortunately H. macrophylla  is the variety most susceptible to winter bud injury in Southern Ontario. Our winters can be  severe, so you might need to offer it some winter protection from severe winds to protect the flower buds. Tying the branches together and wrapping them with burlap isn’t pretty, but it could mean winter survival. Remove the burlap when the buds begin to swell.

‘Annabelle’ is one variety in the species H. arborescens. Its  blooms may bring lollipops to mind. They are usually very large, and made up of tiny individual blossoms. There is one trait that sets ‘Annabelle’ apart from most other hydrangeas – the blooms open green, turn white for 2-3 weeks, and gradually turn green again (at which time they can be used in dried arrangements). These huge blooms are notorious for falling over in wind and rain storms.

H. arborescens  bloom on new wood.( Stems that developed on the plant during the current season) So late winter or early spring is the time to prune. Just look for the first set of fat new buds and prune back the stem to just above this new growth.  If you have a lusty plant and want to keep it contained, you can cut back drastically — almost to the ground — in late winter before the new growth appears. Or you can leave more of the woody stem in order to give the heavy heads more support. Cut any dead branches to the ground at any time; they’ll be brittle, so easy to identify.

  • And finally, a brief description of hydrangea varieties and hybrids now on the market:

The most common types of Hydrangeas available are:

·         Hydrangea arborescens (‘Annabelle’ being one of the most well known ones in this group). The flowers are dome-shaped and the leaves are generally heart-shaped thin, matt and floppy.

·         Hydrangea macrophylla (Bigleaf Hydrangea) – Large colourful mophead or lacecap flowers. This is the group that you see blue (under acidic conditions or pink under alkaline conditions). Leaves are generally heart-shaped, thick, glossy and sturdy.

·         Hydrangea quercifolia (Oakleaf Hydrangea) – Can be easily recognized by the leathery oak-like leaves. Flowers are cone-shaped.

·         Hydrangea paniculata (Peegee Hydrangea) – ‘Limelight’ being one of the varieties. These types of hydrangeas can be identified by their cone-shaped flowers.

Familiarity with each type will help you determine when to best prune it and where to place your plant for best results.

Judith King, a member of the American Hydrangea Society put a website together called: Hydrangeas, Hydrangeas! which I find it helps with pruning techniques for each type and offers further general information: http://www.hydrangeashydrangeas.com/index.html

Hope you find this information helpful.