Paraic Horkans Plant of the Month for August is the Hydrangea

Plant of the Month – Hydrangea

The wonderful flowers are reminiscent of coastal Cape Cod or Brittany in northern France.Paraic Horkan
Hydrangeas were first introduced to the British Isles in 1790 and are native to South East Asia and the Americas, both North and South. There are approximately 70 species of Hydrangea with an incredible 600 + cultivars. The word hydrangea comes from Greek: hydro meaning ‘water’ and angeion meaning ‘vessel’ which is believed to describe the shape of the seed pods.

Tolerating both sun and partial shade, Hydrangeas love a moist well-drained soil. They do not like to dry out so the base of the plants should be liberally mulched to help with moisture retention and you should consider watering in very dry weather.

Within the species of Hydrangea most popular in Ireland are deciduous shrubs and evergreen and deciduous climbers. The shrubs can be sub-divided into:

Hydrangea paniculata enjoys more sun than other Hydrangeas. It is a deciduous shrub with a height and spread at maturity of 2m. It has large conical flowerheads and blooms as late as October. Two of the more popular cultivars in Ireland would be Hydrangea p. ‘Limelight’ whose flowers open a pale lime colour turning to white as they mature and Hydrangea p. ‘Wim’s Red’ whose flowers open white, gradually change to pink and mature to a deep rich burgundy.

Hydrangea macrophylia (or Big Leaf Hydrangea) is probably the most well known of the Hydrangeas and can be further subdivided into Mopheads and Lacecaps. This describes the flower structure of the shrub. Mopheads are large pompom-shaped flowers made up of lots of individual male flowers while Lacecaps have a flattened centre of tiny female flowers surrounded by a ring of larger male flowers. Both can be blue, pink, purple, red or white. It should be noted that the Big Leaf Hydrangeas flower on last year’s growth so should not be pruned back too hard. They grow to a full maturity of just under 2m tall and about 3m wide. They are also responsive to the acidity of the soil; the more acidic the soil, the bluer the flower colour. Those grown in an alkaline soil will be pinker in colour. It should be noted that white flowers will not be affected by the soil pH. Particular favourites would be the blue mophead Hydrangea m. ‘Bodensee’ and the pink lacecap Hydrangea m. ‘Shower Teller’.

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The abundance of flowers in late summer make the Hydrangea a wonderful addition to any garden.Paraic Horkan
Hydrangea quercifolia is known as the Oakleaf Hydrangea and is a North American native. It bears large conical white flowers on last year’s growth. It should be noted that this Hydrangea does best with morning sun and afternoon shade and has a mature height and spread of 1.5m and 2m. Its leaves turn purple and red in autumn adding another dimension to this wonderful shrub.

Hydrangea involucrata is a Japanese native which matures to approximately 1m tall and 2m wide. Its leaves are more heart-shaped and its flowers, in blue, pink and white, are similar to the lacecaps but tend to be looser or more open in structure.

Hydrangea serrata is also known as the Mountain Hydrangea and is one of the smaller Hydrangea shrubs with a mature height and spread of just over 1m. Its flowers are lacecaps, the inner small flowers being shades of pale purple, pale pink or white and the outer larger flowers being blue or pink. A favourite for Irish gardeners is Hydrangea s. ‘Bluebird’ whose central flowers are blue and its outer flowers are pale blue/pink.

Hydrangea arborescens or the Smooth Hydrangea has a mature height and spread of 2.5m. It bears large spheres of white flowers which can be up to 25cm. The most popular of the Smooth Hydrangeas is Hydrangea a. ‘Annabelle’.

Climbing Hydrangeas can be sub-divided as follows:

Hydrangea anomala petiolaris is a deciduous self-clinging climber. It bears loose lacecaps of white flowers in summer. It can grow to a height of 15m.

Hydrangea seemannii is an evergreen climber which bears loose lacecaps whose central flowers are greenish white and the surrounding larger male flowers are white. It does well in shady areas and will require some support before it becomes self clinging as it matures.

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