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Hydrangeas are a well-known and commonly grown plant, but many people will be surprised at the different varieties that exist and are less well known. Although I will certainly mention the tried-and-true mop tops, I will also try to enlighten you about the other fascinating members of the Hydrangeaceae family, and the fact that most of them flower only white!
White mop top hydrangeas with oyster plant backdrop
Most people know that the hydra part of the plants name comes from the Greek word for water. It is less known that the angea is from the Greek word for vessel. Anyone who has left hydrangea plants unwatered on a hot day will know that they certainly are vessels requiring a lot of water.
Hydrangea arborscens in Lyon, France
In Sydney, and other warm climate areas around the world, the most commonly grown hydrangeas are the mop tops (Hydrangea macrophylla), in all their various forms. They are grown for large showy colourful flowers, and there are quite a few interesting variations. I will elaborate on these, but also look at some of the other 75 species that exist. I will also look at hydrangea look-alikes that gardeners might like to grow, and which are best for Sydney, and cooler climates.
Mop Top pink hydrangea in Ohio Garden
Mop Top hydrangea blue in Warrawee Garden
Of course, the majority of hydrangeas are shrubs, but there are also some climbers. There are also some genus (i.e. that are in this family but are not botanically hydrangeas), that are worth knowing about and using in our gardens. Some will be known to keen gardeners, but they may not have known that they are of this family.
I will also give you some suggestions on how to prune hydrangeas, and it can be different for different species. Admittedly, pruning can be a bit like a bad haircut, the damage will grow out, but if timing and style of pruning are done more expertly, more flowers and better plant shape will almost certainly result.
White Mop Top
Mop tops can vary in colour from pink to purple, to red, and, of course, white. With the flowers of colour, pH (soil acidity or alkalinity) can make a massive difference to the colour. It is, in fact, possible to change the colour from blue to pink, vice versa and any shade between. White mop tops basically stay white, sometimes perhaps affecting a slight pink or blue tinge.
White, pink and blue mop tops in Warrawee garden
White Mop Tops in Paris florist shop
Winter colour on white hydrangea flower caused by botrytis fungus
Mop Top and Lace Cap hydrangeas together
So there are the normal mop tops, but other major parts of this group are the lace caps, with a cluster of small sterile flowers in the middle and normal size flowers like a constellation around them, and cupped or dimpled hydrangeas. One well known one is Hydrangea macrophylla ‘Ayesha’. The latter group are often only seen in old gardens. They tend to be very tough!
Lace Cap Hydrangea in Bruges
Cupped or dimpled Hydrangea
Old Dimpled (cupped) hydrangea in Roseville Garden
Lace Cap hydrangea in Bruges, Belgium
Mop top hydrangea autumn colour
Still within the mop top umbrella there are the more recently introduced Endless Summer range, developed in the early 1980s in Minnesota USA. They are reported to flower twice in the one year. There are four cultivars available, The Original (a chance sport found in the Bailey’s Nursery in Minneapolis-St. Paul), Blushing Bride, a dazzling white, Twist N Shout, a lace cap form, and Bloom Struck, which has dramatic red stems.
Hydrangea ‘Endless Summer’. Photo by Carol Norquist, NGC Flickr
Climbing Hydrangea paniculata in Strasbourg, France
Other significant and commonly grown species include the climbing hydrangea, Hydrangea anomala ssp. petiolaris, Hydrangea arborescens, Hydrangea serrata (grown in Japan to make a sweet tea), Hydrangea paniculata, with delicate white flowers and Hydrangea quercifolia, known as the oak leaf hydrangea because of the shape of its leaves.
Hydrangea aborescens ‘Annabelle’
Most of these need a cooler climate and, indeed, thrive in it. I know of one climbing hydrangea in Willoughby in Sydney which survives but does not thrive! I am interested to know if other readers in warm climates have had more success.
Climbing Hydrangea in Sydney not looking at all healthy
Hydrangea paniculata in Strasbourg street planter
Of these other species, the only one that I have grown well in the warm climate of Sydney is the oak leaf. It has stunning single or double flowers and pretty autumn leaves (and often flowers) that persist through the winter and drop just before spring and the growth of the new leaves.
Oak Leaf Hydrangea double flower
Hydrangea quercifolia. Photo Helen Young
Oak Leaf Hydrangea flowers
When the double oak leaf is flowering in my garden, passers-by often ring my doorbell or stop their cars to ask what the stunning flower is! I find this species surprisingly capable of coping with really hot weather, even over 40 degrees Celsius!
Single Oak Leaf Hydrangea at Lindfield
Apart from these other species of Hydrangea there are some significant genus members of this family. Philadelphus, the mock orange, and Deutzia are in this family. The less well known Carpentaria and Dichroa are too. Dichroa actually does grow well in Sydney and therefore warmer, more humid environments.
Dichroa versicolour and Dichroa febrifuga are the only other plants in this family for which the flowers come in colours other than white, blue and pink, and also change colour depending on the soil pH.
Dichroa versicolour. Photo Helen Young
Of course, many people do not want to try hydrangeas, as they seem tricky to prune, and seem prone to mildew problems. For these people there are hydrangea look-alikes! Look at the Viburnum opulus Sterile, the Snow Ball tree (very like Hydrangea paniculata and Phildadelphus), Eupahtorium megaphyllum, Kalanchoe blossfeldiana (and the species is crucial), Spirea cantoniensis (May Bush), and even Sedum (now classified as Hylotelephium). All of these will give lovely rich florets reminiscent of hydrangea flowers.
Hydrangeas are fairly easy plants to grow, and are one of the few plants which are tolerant of heavy clay soils. Their biggest problem is probably the affect mildew has on them. I have had some success applying fungicides but feel, as they are not registered for use on hydrangeas, I cannot suggest them here.
Mop top hydrangea leaf showing damage by pests and fungal disease
Do not underestimate the importance of mulching these plants, especially if they are planted where they get a lot of sun. On a hot day, an unmulched garden bed can lose up to 60% if the water applied to it. Bountiful watering is also a good idea in the warmer months (but not on the leaves!).
Mop Top white hydrangea showing healthy foliage just before flowering
Probably the only other consideration for developing beautiful, floriferous plants, other than good mulching and watering, is pruning. The basic rules of pruning for all plants still hold for hydrangeas. Generally cut them back after flowering. Always cut out dead, dying, diseased, thin, or crossing over canes/stems. Also, as with all flowering and fruiting plants, feeding is important, so use slow release, smelly pellets, or foliar feeds, or a combination!
If mop top plants have been left for a while, their canes, or stems, may have become thick and woody, and lose vigour. Vigorous plants are much more likely to flower, of course.
Mop top hydrangea after pruning
If mop tops have been left it might be necessary to cut the plants to ground. If the canes seem healthy and strong, it is necessary to cut back only down a couple of bud pairs (still two year old wood), which should be ideally plump and fabulous. The only mop tops exempted from this treatment is the Endless Summer, pruned after their second flowering.
Hydrangea macrophylla showing new growth after heavy pruning and feeding
Potted Oak Leaf hydrangeas ready for sale
Hydrangea quercifolia are not pruned the same. Ray Rowell, the father of horticulture in Australia, suggested that the oak leaf hydrangeas were best left unpruned except for the removal of the spent flowers. They can become huge if left, of course!
Oak Leaf Hydrangea autumn colour
Hydrangeacea plants can produce generous flowers, in shades from pink to purple, although, in the main, the flowers are white. There is surprising variety apart from the mop tops, which, regardless of where you live, you should consider growing, including the climbing hydrangea and the oak leaf ones.
Also consider easy to grow hydrangea look-alikes, such as Sedum and Viburnum. And also do not rule out the other genus in this family. Hydrangeas are extraordinary plants. Ideally planted in banks, but at least consider trying one or two to give your garden a thrill.
Mop Top hydrangeas in blue and pink in Lunas, France
Another great article, thanks Bernard. Fantastic photos too.
We have some wonderful Hydrangeas here at Wychwood. When it comes to favourites I’m torn between the Hydrangea quercifolia (that autumn colour!) and an awesome, unknown brilliantly blue lacecap hybrid that’s tucked away in the corner of our nursery.
There’s something almost tropical about Hydrangeas as well… Which, for down here in freezing Mole Creek, Tasmania is a welcome sight.
You know Matt, I’d never thought before about hydrangeas looking ‘tropical’ but you’re absolutely right. I guess it takes someone in freezing Mole Creek to notice and appreciate that! But it does explain why hydrangeas can look so at home in such a wide variety of garden climates and styles.
A great detailed article with really good pictures as well. Thanks,
Jeff Howes
Thank you Bernard for another very interesting article. Hydrangeas are fascinating and so gorgeous at all stages. Here in Auckland, the last of mine are now in vases, drying and fading quietly. My white ones, in heavy shade, turned green on the plant. I well remember your fabulous Oak Leaf hydrangeas.
Lovely Bernard, thank you. the climbing hydrangea are to die for, but would I move to France….in JOT! Merci
Yes, Kris, I would love to a cooler climate (and would be very happy for it to be France, too!), so I could grow the climbing hydrangea. I suppose I am glad that there are many plants I can grow in my temperate (for now) climate in Sydney, which people in France would be envious of!
Thanks Bernard. The article did eventually arrive! Fabulous. I had no idea there was such a variety. In Auckland we had lots growing in our garden and usually lots in our home. It was a great informative article with superb photos.
Gill
So glad the articel did arrive. I really feel the oak leaf should be grown more often, stunning flowers, especially the doubles, vivid autumn colour and a shrub that looks quite reasonable through the cooler months when the mop tops look dead or dying! Enjoy Paris!