Plant of the Month: September


by Kate van Heel

Throughout history the hydrangea has been especially significant in Japan, where many believe the flower originated. According to a Japanese legend, the hydrangea became associated with heartfelt emotion, gratitude for understanding, and apology after a Japanese emperor gave them to the family of the girl he loved to make up for neglecting her in favour of business and show how much he cared about her. Pink hydrangeas are especially associated with genuine emotion because their shape resembles a beating heart.

The genus Hydrangea contains about 75 species of shrubs, trees and woody vines, along with hundreds of named cultivars. Hydrangeas are grown primarily for their large flower clusters that vary in shape from flat lacecaps, to long panicles, and large, round mopheads. 

The colour of hydrangeas, except for white hydrangeas, depends on the acidity of the soil. You can make pink hydrangeas turn blue by increasing the acidity of your soil. Apparently you can increase the acidity by adding coffee grounds, citrus peels, and crushed egg shells, although I have never tried it.

One of the most popular hydrangeas is Hydrangea arborescens ‘Annabelle’ .

Hydrangea arborescens ‘Annabelle’

Hydrangea arborescens is a large bushy North American shrub bearing a mixture of tiny fertile florets and larger more showy sterile ones, which in fact have coloured bracts in place of petals. Hydrangea arborescens ‘Annabelle’ has only sterile florets, which makes the flower heads much larger, like spectacular white balls up to 30cm across. The Royal Horticultural Society has given it an Award of Garden Merit (AGM). However, its only failing, I think, is that the flower heads are so heavy that after a downpour the whole shrub flops over and never really recovers its former glory. I have tried both cutting the shrub back very hard in Spring to 30cm, and also pruning less severely but to no avail. However, Sarah Raven recommends Hydrangea ‘Incrediball’, a new variety of Annabelle type Hydrangea from the USA, that boasts giant flowers on very strong stems. It apparently produces strong, sturdy stems which support giant, football-sized blooms – hence the name ‘Incrediball’. They are meant to be tolerant of all the wind and rain that a British summer can throw at them, so perhaps it is a better option.

Another of my favourites is Hydrangea paniculata ‘Limelight’. It opens a  bright acid-green then the flowers fully flatten and turn pure ivory, before being washed with rich pink.

Hydrangea paniculata ‘Limelight’

It likes a cool, semi shaded part of the garden where its flowers will stand out and doesn’t flop after rain. Although the only essential work is to remove dead wood in spring, it will flower more prolifically when pruned back annually to a framework of branches. Each spring, cut back last year’s stems to a pair of healthy buds to maintain a permanent framework.

My third choice is Hydrangea aspera. H. aspera is an erect deciduous shrub to 3m tall, with softly hairy, lance-shaped leaves to 25cm long and flat flowering heads with purple fertile flowers and showy white, pink or purple outer sterile flowers in late summer, which are attractive to bees and butterflies. Like Hydrangea quercifolia, this needs only minimal pruning in spring to remove dead and over-long stems. A new addition to my garden is Hydrangea aspera ‘Hot Chocolate’. The underside of the leaf is striking burgundy, whilst the top is chocolate brown, fading to deep green later in the season. The flower colour is pale peach/pink which contrasts well with the leaves. This is planned to replace a pink Annabelle which has decided to flop unacceptably.

These are my three choices but there are so many beautiful hydrangeas to choose from.  Most hydrangeas will remain in flower well into September, so there is a generous selection of stunning varieties to choose from. Also the final flowerheads of the year can be left on the plant to provide winter interest.

Hydrangea aspera Villosa Group


Hydrangea arborescens ‘Annabelle’ and H. aspera Villosa Group by permission of HPS Image Library

Hydrangea paniculata ‘Limelight’ copyright Kate van Heel

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