Hydrangea is a flowering plant found in different parts of the world in many different climates. Some species are native to China. The Chinese names of the flowers are 繡球花, 八仙花, 紫陽花, etc. It is a deciduous shrub growing to 2 m tall by 2.5 m broad with large heads of pink, blue or white flowers in late spring and summer.
The inflorescence of Hydrangea is a corymb, with all flowers placed in a hemisphere or even a whole sphere in cultivated forms. Two distinct types of flowers can be identified: central non-ornamental fertile flowers and peripheral ornamental flowers, usually described as “sterile”. Some ornamental varieties are all sterile. More studies on the floral structures will be done later on.
Flowering lasts from early summer to early winter. The fruit is a subglobose capsule.
Hydrangeas are amazingly versatile in that you can actually alter the flower colours to suit your needs. The flower colour in most forms relates to the acidity or alkalinity of the soil. In acid soil (pH 5 or less) hydrangeas are usually always blue. As the soil pH climbs towards the neutral and alkaline end of the scale (pH 7 or more) hydrangeas turn mauve, pink and red. A blueing tonic (containing aluminium and iron) will turn pink or mauve hydrangeas blue. A cup of lime (calcium carbonate) added to the soil in spring will cause blue or mauve hydrangeas to turn pink. White flowering hydrangeas will remain white regardless of soil pH.
However, in my garden a purple flower plant is planted together with a pinkish-blue flower plant under soil of the same pH, their different phenotypes can still be expressed.
Before next Spring, I will adjust the pH of the soil and see if the plants will change the colour of the flowers.
Development of the Hydrangea inflorescence
Close-up view of the white inflorescence
Many botanists consider those flowers where stamens and pistils are under developed and lack function as neutral flower. However, near the end of the life of the white flowers, the petals eventually open and the stamens and pistil are exposed.
No development of the flowers into fruits have been observed in these commercial varieties of Hydrangea.
Young inflorescence of Hydrangea with lilac ‘flowers’
Chinese drawings / paintings on Hydrangea
Oil painting on Hydrangea
Chao Shao-ang (趙少昂) (1990) A Study of Chinese Paintings, Publisher: Ho Kung-shang, Art Book Co., Ltd, Taiwan, ISBN 957-9045-22-4