Hello again hydrangeas
Gardeners are rediscovering these vintage beauties once considered fit only for granny’s patch.
tVirtually all the hydrangeas grown in New Zealand are cultivars or hybrids of species native to Japan, China and the United States.
hey’ve been talking about it for some time now, the comeback of that classic nana flower, the hydrangea. For some of us though, hydrangeas never went away of course. Well-known Taranaki nurseryman and gardener Glyn Church is one of their staunchest advocates and author of two books on the subject. Glyn began growing and collecting hydrangeas at Woodleigh Nursery & Gardens in the early 1990s when they were “completely out of fashion”.
Although he sold the Woodleigh name and nursery to Janica and Quin Amoore in 2011, Glyn is still crazy about hydrangeas. “I first got into them when Graham Smith, the former director of Pukeiti Gardens, suggested hydrangeas as summer colour for our garden. I got hooked. I then propagated some for sale. At the time they were so unpopular – I make the joke hydrangeas were like kittens, you couldn’t give them away,” he recalls. “Once hooked, I began talking to people in other countries about them and accessed lots of new varieties, mostly as young plants but also some seeds of species or wild ones as we had our own quarantine house.”
Most of Glyn’s hydrangea plants came from France, Britain and the US. He would also often search through the gardens of abandoned homesteads here in New Zealand seeking older, resilient varieties. He sourced seed mainly from Asia – China, Korea and Taiwan. “I’ve done a bit of breeding and selecting but it’s hard to beat existing plants,” he says. “That’s why we imported varieties which were not available in New Zealand, such as ‘Merveille Sanguine’ which I renamed by turning those two words around to ‘Bloody Marvellous.’”
The focus of his more recent breeding work is a close relative of the hydrangea, Dichroa versicolor (recently recognised as a hybrid of the Vietnamese species Dichroa
febrifuga and Hydrangea macrophylla), often labeled the evergreen hydrangea. “We discovered that hydrangea and dichroa naturally interbreed. Intergeneric hybrids are extremely rare – usually pears breed with pears and not with apples! We selected and named some of our seedlings ‘Summer Skies’ and ‘Cambridge Blue’, which are sold by Woodleigh. Both are evergreen.”
Get to know hydrangeas
There are roughly 75 species in the Hydrangea genus, most of them growing naturally in south and east Asian countries such as Japan, China and Korea, with several species native to the US. The first hydrangea to arrive in European gardens was
Hydrangea arborescens, dispatched from North America by farmer and plant hunter John Bartram in 1730. He and son William then discovered the oak-leaved hydrangea ( Hydrangea quercifolia), native to Georgia.
Around the same time, mophead and lacecap hydrangeas were discovered in Japan by Engelbert Kaempfer, a physician working for the Dutch East India Company. But it was well nigh impossible at that time to remove any botanic samples from Japan, which was then a closed society. It was more than 150 years later that English botanist and plant collector Charles Maries was able to take samples of Hydrangea macrophylla and
Hydrangea serrata to Europe. Today, virtually all the ornamental hydrangeas we grow are cultivars or hybrids of species native
to Japan, China and US. Most widely grown is Hydrangea macrophylla, which has over 600 named cultivars of either lacecap or mophead types.
In the wild, Hydrangea macrophylla flowerheads are all lacecaps. Mopheads descend from a naturally occurring “sport” that breeders have continued to develop, says Glyn.
Both lacecaps and mopheads are resilient plants that are tolerant of both shade and sun, with some growing well in coastal locations. Indeed hydrangea mopheads have naturalised on some islands in the Hauraki Gulf, particularly the south-facing bays of Kawau Island.
Other popular Asian hydrangeas include Hydrangea paniculata, known for its big snow white flowerheads, easy care and cold tolerance, and
Hydrangea serrata, one of Glyn’s favourites. Growing naturally in woodland and mountain areas of Japan and Korea, this latter species is not as tolerant of drought, wind and heat as Hydrangea macrophylla.
Sometimes described as the tree hydrangea, Hydrangea aspera subsp.
villosa is a large shrub that can grow to over 3m. It produces beautiful lacecap flowerheads that have white or pink on the outer edge, with mauve or blue centres.
A less common Asian species is the deciduous climbing Hydrangea
anomala subsp. petiolaris, found in the same territories as Hydrangea
serrata. This self-clinging vine has lacecap blooms in early summer. The two North American species
Hydrangea arborescens and Hydrangea quercifolia are very cold hardy, hence their popularity in regions with heavy frosts. Most selected forms of Hydrangea arborescens produce large white flowerheads, are happy in sun or shade, and drought resistant. The creamy white blooms of oak-leaved Hydrangea quercifolia are cone-shaped and the various forms of this drought-tolerant species grow well in shade or sun (more so in cooler regions). In fall, the leaves of oak-leaved hydrangeas turn burgundy and red, and their flowers also take on a pink tinge.
Hydrangea problems
They don’t have many, and it’s this easygoing nature that makes hydrangeas popular with gardeners. “Fungal diseases such as botrytis and mildews can be a problem in wet or humid climates, especially when plants are under stress,” says Janica Amoore. “Good hygiene and maintaining healthy plants can
“At the time hydrangeas were so unpopular – I made the joke that hydrangeas were like kittens, you just couldn’t give them away.”
help to manage these. Root rots can be a problem for the arborescens, aspera, paniculata and quercifolia species, most likely phytophthora, which is encouraged by wet soil and humid conditions,” she adds. “Minimising root disturbance when planting, applying trichoderma (a protectant fungi) and avoiding excessive watering or waterlogged soils will help to avoid this.” If the buds of your Hydrangea
macrophylla variety have been killed or damaged by frost, remove them and prune back to healthy wood above a bud. Gardeners living in colder regions who want to grow cultivars of this species should look out for newer, remontant varieties that will produce new stalks during summer from below frosted buds.
Flower structure
There are three types of hydrangea flowers: globe-shaped mopheads, flat clusters of lacecaps and cone-shaped panicles (particularly Hydrangea
paniculata and Hydrangea quercifolia). All these produce a mix of small, insignificant true flowers and larger modified bracts or sepals of what Glyn describes as “pretend” flowers. These sterile, colourful pretenders attract insects to the flowerheads, which then pollinate the true flowers.
As the blooms age, the colourful outer sepals gradually change colour. This is most obvious in cultivated hydrangeas, particularly mopheads which produce only a few true flowers, hence the longevity (up to six months) of their flowerheads.
Colour changes
Unlike other hydrangeas (and any other plant for that matter), Hydrangea
macrophylla cultivars and hybrids have the ability to change the colour of their blooms depending on the acidity of the soil they are in. Acid soils result in blue flowerheads; more alkaline soils mean your blooms will be pink or red.
However, it’s not just acidity that turns hydrangea blooms blue, it’s also the presence of aluminium ions in the soil. This is why the regular addition of aluminium sulphate to soil can turn pink hydrangeas blue, with lime doing the opposite.
However, Glyn and other experts question the worth of this practice, believing it’s far better to work with rather than against nature, and choose cultivars that will give you the best colour for your soil.
Propagation
Hydrangeas grow easily from cuttings, particularly Hydrangea
macrophylla and Hydrangea serrata. It’s best to take these from new growth, cutting a piece about 10cm long just below a node. Remove lower leaves, place the cutting into a pot with potting mix and keep moist. Some gardeners cover the pot with a plastic bag or similar to maintain moisture levels.
Pruning
Like other shrubs and trees, pruning out dead, weak and diseased wood is important for all hydrangeas. Likewise pruning to improve shape, and thinning to let in light and reduce crowding. Most benefit from the removal of spent flowerheads too. You can also prune Hydrangea
macrophylla and Hydrangea paniculata types to increase the size of flowers. Generally, the harder the prune, the larger the flowers.
For Hydrangea arborescens cultivars, the pruning regime can be as simple as removing spent blooms. Alternatively, you can cut back lightly (a third to half the previous season’s growth) or heavily (down to ground level).
Always prune hydrangeas in winter (early spring in frosty places). For macrophylla and serrata types, Glyn suggests retaining a good number of fat flower buds for a good display. For larger blooms, after removing spindly growth and so forth, cut stems down to the lowest set of fat flowering buds. This doesn’t apply to other species of hydrangeas as they don’t have overwintering flower buds, instead producing blooms on new summer growth.