Hydrangeas produce showy heads in a variety of forms from lacecap, to rounded mophead, to showy lilac-like panicle. They owe their diversity to the fact that the twenty-three species are now divided between America and Asia following the Continental Drift which split up the single land mass.
Find out how to grow hydrangeas.
The difference between Asian and American varieties
To generalise, the Asian species tend to thrive on moisture and they prefer rainy summers and an ambient climate for nine months of the year, although they are hardy enough to survive cold winters. This weather pattern mimics the rainy season found all across Asia. The main Asian species is Hydrangea macrophylla, but others include H. serrata and H. paniculata. There are also climbing and evergreen species.
The Asian species also prefer acid soil and they will only produce flowers if the pH is low enough. Add sequestered iron, or place rusty iron impalements close by, or grow them under pines. All three make the soil more acid. This is why the best hydrangeas in England are found in acid pockets in the western half of Britain.
The American species are much more drought tolerant and they could be grown all across Britain in all types of garden. The flowers tend to be in a less showy spectrum of colour - creams, whites and pale-greens. But these are colours that glow in gloomy light and, as the flowers fade, shades of pink creep in. These American species grow happily on lime and even chalk.
Hydrangea arborescens is a native found from Louisiana to Florida and northwards to Iowa. There it survives the snowy winters and hot, dry summers of Iowa and will happily grow anywhere in Britain, regardless of rainfall or temperature. 'Annabelle' is the best form with flat-headed white flowers appearing from July. The green veining on the four "petals" (which are in fact long-lasting bracts) prevents 'Annabelle' from looking brash in summer sun.
This plant was discovered growing wild near Anna in Ohio, hence the name. It was launched in the mid-1970s by the Gulf Stream Nursery and is now widely available. These hydrangeas bloom on new wood so frost does not effect flowering. Cut down in late spring to the shooting buds.
Two new forms of Hydrangea arborescens from America
From Madrona Nursery, has longer-lasting double flowers, although not quite as white.
The first pink arborescens developed by Dr Tom Ranney at North Carolina State University's Mountain Horticultural Crops Research Station.
The oak-leaved hydrangea is another American species with large, lobed leaves that turn red in autumn. Heavy triangular heads of flower appear in late-summer to autumn and they are almost horizontal - so this is a good plant for a container, or for overhanging a wall. The two best known named forms are 'Snowflake' and 'Snow Queen' - both a cool white.
The Asian species
Award-Winning AGM Varieties - but flower colour depends on soil pH.
Maroon-coloured stems - pallid mophead flowers in pink or blue depending on soil pH.
Elegant white lacecap (1903).
Bright-rose to red lacecap.
Blue-budded pale grey-blue lacecap.
'Madame Emile Mouillière'
The finest white mophead for late use.
White starry lacecap.
'Générale Vicomtesse de Vibraye'
Earliest clear-blue mophead.
Wiry small shrubs, perfect for small gardens, with good red autumn colour and smaller lacecap flowers. Ashwood Nurseries have the best collection.
A very old Japanese variety, often seen in their old paintings. Flowers in June, white flowers with few ray florets which age to pink. Upright growth to about 1 metre (3ft), with reddish foliage and stems later in the season. 1.5 m (5 ft).
(Japan) AGM 1992 (syn. Aigaku) A lovely small to medium-sized shrub covered with very shapely lacecap type heads. Flowers in early summer and repeats in autumn. Grow in sun or shade, pink or blue flowers according to soil type. Leaves change from green to reddish brown as the season progresses.
(Haworth – Booth pre 1970) Best grown as blue, this is a lovely dwarf shrub with a long flowering period. Rather uneven lacecap flowers with serrated edges to the florets and foliage which changes to reddish purple in autumn. Needs a sheltered spot to avoid spring frosts. 1.25m (4ft 1in).
Lovely golden foliage in spring which fades to green as the flowers develop. Upright growth, with many pale lacecap flowers.
(Chambers 1888) AGM 1992. A tall, slender lacecap with white florets, gradually changing to deep pink from the outer tips. The individual florets are unevenly shaped, serrated and very beautiful. They reverse with age displaying their deep crimson backs. This shrub improves with age, flowering from June until late October. 2m (6ft 7in).
A taller shrub with almost luminous medium sized lacecap flowers with both fertile and sterile flowers of rich blue. 1.5 to 2m (4ft - 6ft).
(syn. Var. Kiyusumensis) A plant with thin, wispy growth, but delicate lacecap flowers. The sterile florets are white and beautifully edged in rose-pink. Discovered originally on Mount Kiyosumi in Chiba Province, Japan, it has been used to produce some very striking cultivars.
A white flowered lacecap variety. Four or five ray flowers surrounding the white fertile flowers. The ray florets turn red in bright sunlight. A dwarf plant which needs some shelter to do well. 1m (3 ft).
(Haworth-Booth pre 1980) Neat little lacecaps with 6 to 10 sterile florets in shell pink or pale blue depending on soil. Fertile flowers are generally blue. A dwarfish shrub suitable for a patio container with a long flowering season and tidy habit. Up to 1m (3 ft).
(Japan) A free flowering white lacecap variety with green fertile flowers. Bushy and neat forming a small shrub. 1m (3 ft).
Large, clean lacecap blooms of shell pink, or mauve-blue on acid soil. Very free-flowering when well grown. Florets are irregular with one sepal larger than the rest.
(Foster 1992) Small pink or blue lacecap blooms in great profusion on medium sized bushes. Easily grown, hardy and very reliable for summer colour in the shrub border, with deep claret red foliage colours in autumn. Long lasting interest and one of the best serratas. 1m (3 ft).
An oriental variety capable said to need lime-free soil but I also grow the following in my Cotswold garden quite happily. Best in shade in rich, well-fed soil. They make a late-summer feature and they are planted all over Battlestone Hill at RHS Wisley to great effect.
Lime-green to white lilac-shaped heads of flower. Medium to small sized shrub, subtle and lovely.
Very large shrub (up to 20 ft) with white flowers ageing to pink - loved by landscapers.
Huge bright-white heads - you either love it or hate it.
Much broader-based panicles of flower - white speckling to pink.