A Guide to Understanding Hydrangea
Few flowering shrubs provide such elegance and grace in a garden as Hydrangea. Add in the bonus that they bloom from summer to fall and you’ve quite possibly found the perfect shrub for the St. Louis region.
Yet while they are amazingly beautiful and surprisingly easy shrubs to grow they can be a bit overwhelming.
Some of the most common questions regarding hydrangea that come into the garden center are: Do all hydrangeas require shade, what is ‘old wood’ and ‘new wood’, when do I prune, is there more than one kind of hydrangea and are you intentionally making this hard to understand? In answer to the last question…no, not intentionally…really, I promise. In fact hydrangeas are quite easy to understand once you know the four main species of hydrangea and (most importantly) what kind is growing in your garden. Here they are:
Hydrangea macrophylla (Endless Summer, Nikko Blue) – These include the old garden varieties such as Mophead, Big Leaf, and Lacecap types. The most common variety planted in St. Louis is ‘Endless Summer’ and most H. macrophylla will bloom blue, pink or shades of purple. These require shade so they do not burn in our summer heat. With the exception of ‘Endless Summer’, Hydrangea macrophylla bloom on ‘old wood’, but I’ll get to that later…
Hydrangea arborescens (Annabelle, Invincibelle Spirit, Invinciball) – These varieties are most often white with the exception of ‘Invincibelle Spirit’ which is a pale pink. While H. arborescens does best in morning sun and afternoon shade I have my ‘Invincibelle Spirit’ in full sun and thus far it appears to be doing well. H. arborescens bloom on ‘new wood’.
Hydrangea quercifolia (Oakleaf) – Oakleaf hydrangea have white blooms that typically fade to pink in the fall and while they can survive in partial shade they perform best in full sun. H. quercifolia bloom on ‘old wood’.
Hydrangea paniculata (Limelight, Tardiva) – H. paniculata, or panicle hydrangeas, have white blooms, many of which also fade to pink and occasionally dark pink in the fall. They require full sun for best performance and bloom on ‘new wood’.
Now for the biggest question: What is ‘new’ and ‘old’ wood and when should I prune my hydrangea?
While you don’t need to know the exact variety of hydrangea in your garden, to properly prune it you will need to distinguish between these four species. Luckily, identification is easy since they look very different from each other. After you have figured that out you will know what variety is ‘old and new’ wood and how you need to prune.
Old Wood: Stems are considered old wood if they have been on the plant since the summer before the current season. Hydrangeas that bloom on old wood begin developing their bloom buds for the next year in August and September of the current year. It’s not as confusing as it sounds it just means that if you have a H. macrophylla or H. quercifolia (see above) you need to prune before August to insure that your hydrangea will have blooms the following year.
Often times when people tell me their hydrangea isn’t blooming it was either a hard winter and last seasons stems died down or, most often than not, they were pruned at the wrong time of the year. Typically H. macrophylla and H. quercifolia simply require only dead tips or old stems to be trimmed out to maintain appearance. If necessary to control the size of the plant, cut back before late July to allow for buds to develop. Yes, this means you will be cutting off your blooms for this year so it’s best to plant hydrangeas where they have enough space to grow.
New Wood: New wood simply means that they set flower buds on current season wood which makes them easier to maintain. Both H. arborescens and H. paniculata fall into this category. H. paniculata is quite possibly the easiest hydrangea to grow. Sizes of varieties range from 3 feet to 10 feet so you can almost always find the right fit for your garden however, pruning can be done in the fall or late winter if needed. H. arborscens are great for hedges or in masse as they tend to be a bit floppy, but they can also be pruned drastically to control size. This should be done in the late fall or winter although I have been known to prune back unruly Annabelle’s mid season.
The exception to the rule: Okay, you think you have all this information under control and are good to go but then those darn plant people throw one more kink in the chain. ‘Endless Blooming’ varieties – these you will know and quite honestly are most familiar with, in fact you probably have one in your garden.
Hydrangea macrophylla ‘Endless Summer’ and other varieties in the Endless Summer series fall in this category. Basically they bloom on old and new wood this means it blooms early in the season on old wood and then blooms later on new wood. Therefore, you will treat it as you do for both old and new wood hydrangeas with a slight pruning of the first faded flower stems to half their length to encourage new growth and buds as well as after the last bloom in the fall strictly to control shape and height.
So, you can simply leave your ‘Endless Summer’ alone because it’s a gorgeous, no fail, can’t mess it up hydrangea and if you have to read one more confusing word on hydrangeas your head just might explode. See – not confusing at all.
But no matter how you look at it, hydrangeas are perfect for any garden and we; the garden center staff, professional gardeners, horticulturists and master gardeners of the world will always be here to confuse, (ahem) I mean answer all your questions! Happy Gardening!!