Hydrangea conjures images of great mounds of shrubs smothered with mops of pink, purple, blue and white, perhaps under the shade of trees surrounding Victorian villas, or basking in the sunshine by seaside cottages. They may look a little old fashioned, and perhaps they have not been as popular as those fragile, flimsy perennials in recent years. However their ability to deliver late summer and autumn shrub colour and interest, and the availability of a wider range of different types of hydrangea, means they are back on the scene in a big way.
First let’s cover a few of the key points in hydrangea cultivation. These are the things to remember when you select and grow them:
The best known hydrangea, the garden classic is Hydrangea macrophylla (meaning big leaves). There are varieties with mophead and lacecap flowers. The former have those rounded, sponge-like flowerheads of large, usually four-petalled florets. The latter have flattened heads of tiny bead-like fertile florets surrounded by a ring of larger sterile florets.
Some Hydrangea macrophylla and Hydrangea serrata varieties turn from pink and red to blue on acid soil. This can also be achieved in pots using lime-free soil and hydrangea colourant. If you want a blue mophead or lacecap hydrangea then you must choose one which will turn blue; not all do. White hydrangeas do not change colour according to soil type, but they may blush pink in the sun.
Hydrangea paniculata varieties have conical, lilac-like panicles of sterile and fertile florets in late summer. These often start to flower after the macrophyllas and their flowers are shades of white and cream, some flushed pink. Their growth habit is different: stems are upright or arching and the flowerheads are carried at the ends of the current season’s growth. Pruning in late winter is essential to encourage vigorous upright growth; they are best pollarded to the same height each year.
Hydrangeas grow well in sun or light shade. Hydrangea arborescens is particularly good under the light shade of trees. This has soft felted leaves and rounded heads of small florets that are crowded together to create spectacular effect. It needs cutting back hard to around 15cm, 6inches in late winter to encourage strong upright stems. Often the weight of the flowerheads of the most popular cultivar, Hydrangea arborescens ‘Annabelle’ weighs the stems down in summer. Take this into account when you plant it and partner it with a shrub that will lend support: Cornus alba ‘Sibirica ‘Variegata’ works well.
There is a newer variety of Hydrangea arborescens available called ‘Incrediball’. This theoretically has larger flowerheads and stronger stems which do not flop. I remain unconvinced; perhaps I am just put off by the name. What went through the grower/breeder’s mind? This is unlikely to be appealing to anyone likely to grow this plant. Anyway, personally I remain faithful to ‘Annabelle’ despite her occasional unruly habits.
Hydrangeas do make excellent long-term subjects for pots and containers and will certainly deliver more in late summer than most seasonal bedding plants. Use large pots and a loam-based growing medium; ericaceous if you are trying to keep a blue hydrangea blue. Actually I think some of the smaller varieties of Hydrangea paniculata are the best for pots and containers. You cut back hard in late winter so control the size of the plants. They are usually later into growth than the macrophyllas so are less susceptible to frost damage. They are also light and pretty and good in semi-shade for that difficult situation near the house.
One of the most commonly asked questions about hydrangeas is: “Why won’t my hydrangea flower, it was beautiful when I bought it?” Feeding is not often the answer.
It could be because you are pruning incorrectly. As I said Hydrangea paniculata and Hydrangea arborescens are cut back only once in late winter, then left alone. Hydrangea macrophylla varieties are pruned in early spring. Leave flowerheads on over winter, then remove in early spring cutting back to the first pair of fat buds behind each flowerhead. On older plants cut out some of the dark, branched stems to give the newer light stems more space. If you cut back hard every year flowers are usually sacrificed.
The other reason a hydrangea may not flower is that it is a variety that has been developed for the pot plant market and it is not really suited to colder garden conditions. This will of course depend where you are gardening. So if you want a good reliable garden hydrangea choose a named variety that has been bred for garden use.
The ascending popularity of hydrangeas is endorsed by the selection of Hydrangea ‘Miss Saori’ as Plant of the Year at RHS Chelsea Flower Show 2014. Bred in Japan this has semi-double florets of ice-cream white, edged with pink and red-flushed foliage. The breeder assures us it is hardy and compact and will make a great container plant or shrub for the small garden. It is available this autumn from hillieronline.co.uk http://www.hillieronline.co.uk/products/plants/shrubs/hydrangea-macr-miss-saori-9cm.html
Hydrangeas will grow on most reasonably well-drained fertile soils. Although I have seen Hydrangea macrophylla thriving on river banks in Japan it certainly struggles with waterlogging. Conversely hydrangeas do not like drought, despite their ability to grow under trees. The mophead and lacecap hydrangeas seem to be the ones that struggle most with extremes. As for feeding, any slow release balanced fertiliser is ideal; rose or shrub food with trace elements. An annual application should be sufficient.
These hydrangeas are just a few of 300 hard-working, reliable shrubs featured in my new book, The Creative Shrub Garden published by Timber Press. I use hydrangeas and a host of other wonderful flowering and foliage shrubs to create simple but effective plant combinations that work in gardens of all sizes. To order your copy click here: