Hydrangeas

Hydrangeas

Hydrangeas are one of our most popular groups of flowering shrubs, and they should be. Large flower clusters that bloom over a long period of time are a real eye catcher. And with so many great selections, it’s easy to find one you will like, but it can also get a little confusing. Here are a few insights to help make your selection process a little simpler.

We do four different kinds, or species, of hydrangeas. (We actually do a fifth species, but Climbing Hydrangea (Hydrangea anomala subsp. petiolaris) is a vine and won’t be discussed here.) From those four types we have dozens of different offerings. Each species has some general characteristics that make it a little different from the others, and knowing some of those differences is important.  

First, a few lessons in Hydrangea terminology.

We start with...fertile vs. sterile.

Hydrangea’s impressive blooms are made up of lots and lots of smaller flowers. Upon closer examination, on many selections you will often be able to find flowers of two different sizes within each floral cluster. Some will be larger, the size of a quarter or maybe a half dollar piece; others will be smaller, about ¼’ in diameter. The smaller ones are fertile flowers that produce seed. The larger more showy ones, are sterile. It’s these sterile flowers that intrigue gardeners. Most popular selections have floral clusters that contain very large percentages of sterile, or “showy” flowers, and in many cases, blossoms maybe made up entirely of sterile flowers.

Here’s the second set of terms...lacecap vs. mophead.

lacetop

In the wild, floral structures are made up of mostly fertile flowers, adorned with a few adorned with a small number of sterile showy flowers. In some species, the blossom is a rounded, flat-topped cluster, ringed by larger sterile flowers. This floral composition is commonly referred to a lacecap.

While attractive, this floral composition certainly doesn’t catch the eye nearly as much as many of today’s popular garden forms. Most of these selections have floral structures composed primarily of all sterile flowers, producing a large rounded floral structures commonly referred to as a mophead.

mophead

It’s easy to see why the mopheads are gardener favorites. They are stunning! Their large showy floral clusters make an amazing show.  

Now, a third set of terms...old wood vs. new wood.
The first two sets of terms were interesting if you want better understand what you are looking at or better understand floral description you may be reading, but this last set is really important if you want to make sure you know how to grow this garden beauty successfully.

Some flowering shrubs produce flowers from buds created the previous season. These buds remain dormant until the follow spring when they emerge to put on their show. These plants are said to bloom on “old wood”. Other flowering shrubs produce flowers from buds created in season on the current year’s new growth. These are blooming on “new wood”. Understanding this concept and knowing which plants bloom on old wood and which bloom on new wood can help prevent pruning mishaps. Prune a flowering shrub that blooms off of old wood during the late summer, fall, winter or early spring, and you will be pruning off flower buds, and no buds means no flowers. Conversely, things that bloom off new wood can be pruned aggressively during those times without any fear of cutting into flower production.

In the Hydrangea world we find both and know which is which saves a lot of frustration. Cut back a hydrangea that blooms on new wood during early spring cleanups...no problem. The new growth of the season creates all kinds of wonderful flowers and everyone is happy. Cut back a hydrangea that blooms off of old wood at the same times...say goodbye to your flowers. That doesn’t make for happy gardening.

Now for a quick look at the four Hydrangea species we grow.

Smooth Hydrangea (H. arborescens) -This is one of the most dependable and easy to grow hydrangea species. It is a U.S. native, it is very hardy and it blooms reliably. It produces flowers off of new wood in the spring, so heavy pruning at the start of the season doesn’t bother it, in fact it’s recommended. Although the species generally produces lacecap-type flowers in the wild, these forms are rarely seen in gardens. Mophead selections are what really catch the gardener’s eye, and one of the best of those is a called ‘Annabelle’.

It produces large white floral clusters (up to 8-12” across!) and produces those in large numbers. This selection pretty much represents all of the Smooth Hydrangea found in the nursery trade. It grows about 3-5’ tall with a similar spread and does best in light shade. It looks best when pruned back hard each spring, taking last year’s stems back to 6-12” tall. It adds a nice brightness to shade gardens and is one of the easiest Hydrangeas to grow.

Bigleaf Hydrangea (H. macrophylla)-This native to Japan looks a lot like Smooth Hydrangea with one big exception, the color of the flowers. Instead of white, this species has flowers of pink, red, lavender, purple or blue borne in both lacecap and mophead floral stuctures. Many different forms exist offering a myriad of flower color, plant size and floral structure combinations, making their popularity understandable...in other parts of the country. Their use here is less common because of two major cultural problems, they are borderline winter hardy for us and they bloom off of old wood...and that’s not a good combination. If cold temperatures kill back topgrowth, then blooms the next season are scarce to no existent. That makes this species difficult to enjoy here in NE Kansas, and that has unfortunately prevented this species from being a major garden plant in our landscapes...until recently that is.

About 10 years ago, a new selection made its way into American gardens. Known as ‘Endless Summer’, this new form came by way of a chance discovery in the growing fields of a large wholesale grower. The original plant was observed blooming very late in the season, something this species doesn’t do. Upon further evaluation, it was found that this specific plant had the ability to bloom not only in the spring off of old wood, but again later in the season off the new wood. That almost guarantees floral production in climates like ours where this species tends to freeze back precious budwood each year! This new find, ultimately named ‘Endless Summer’, has given many gardens in colder areas the chance to enjoy the blooms of this species. However, in our hot dry climates, we have found that ‘Endless Summer’ isn’t very happy and overall success with this form has been less than what we had hoped for. A newer selection known as ‘BloomStruck’ is improving our chances for success. This selection is proving to be not only tougher, but also appears to have even more reliable blooming habits.

In general, this species gets about 3-5’ high and wide and does best if situated out of the hot afternoon sun. If will need regular watering during hot, dry summer months and most importantly, don’t prune it back! Remember, this species produces its spring flowers off of old wood.

One more interesting feature of this species is the ability of the flowers to change color. If you flowers are pink, you can make them blue by adding aluminum sulfate. If they are blue, and you’d like to make them pink, add limestone. It’s just like magic!

 

Panicle Hydrangea (H. paniculata)-An Asian species enjoyed by American gardeners for a very long time, this large shrub (6-10’ tall and wide), produces large cone-shaped panicles of pure white flowers (sorry, no blue here!), blooming off of the new wood of the season. That makes them hard to screw up! They typically bloom mid-summer, although there are forms that bloom as early as June (‘Quickfire’) and others that hit peak as late as September (‘Tardiva’). There are also a whole host of selections that offer different looking blooms (more or less sterile florets), larger or smaller panicles and more recently, dwarf sizes (3-5’ tall and wide). We carry a number of different selections and all make great plants. This hydrangea actually prefers more sun than the others, although light shade through the worst of the summer may be beneficial.

One interesting feature on this species is the occasional production of pink flowers. The flowers actually are still white, but towards the end of the bloom sequence, if the weather is right (cooler weather, especially at night), you will sometimes see the flowers fade into a rose-pink as they finish. Despite what you may read or hear about, this is unfortunately a fairly rare occurrence in our climate but it does occasionally happen, so enjoy when it does!

Oakleaf Hydrangea (H. quercifolia)-This is one of the best! This large American native shrub commonly grows to 6-8’ with a similar spread. It has large, oak-shaped leaves and large, cone-shaped flower clusters of pure white, much like Panicle Hydrangea. It blooms off of old wood, so don’t prune it during the dormant season! It has good winter hardiness and produces flowers reliably every year. The straight species is common grown in gardens and is impressive, but there are also many popular selections that offer variations in floral characteristics and variations in overall plant size, including many good dwarf forms. It does best when planted in areas that receive light shade, especially through the heat of the day.

 

One added plus to this species is great fall color. As cool weather sets in, leaves will change to red, orange, yellow and burgundy. It’s quite a show! This species can also have flowers that fade from white to rosy-pink towards the end of the blooming sequence, although this is rare for us in our climate as well.

There are many great hydrangeas to choose from and deciding between them may be difficult! Feel free to come out to the nursery and ask us some questions. We can show you some different options and give you some suggestions. If you want to check out all of the different Hydrangea offerings we have, you can follow this link to our online catalog to read more about them.

Have fun!