The hydrangea is native to China, and was introduced to England and then to the United States in the 19th century. Hortensia hydrangea, or "Hydrangea macrophylla" for its botanical name, is also known as florist hydrangea, and is one of the most common species grown. These hydrangeas are popular in the garden, and also as cut flowers.
The hortensia hydrangea is a deciduous shrub that grows between 3 and 8 feet tall with an equally wide spread. It has broad, bushy, dark green leaves and grows spherical clusters of flat, fragrant flowers that range from pink to blue. A few cultivars bloom white. Hortensia hydrangea flowers during the spring and summer months and goes dormant when the weather turns cool. Hydrangeas do not tolerate very cold weather and should only be planted in climates with mild winters. Deadhead flowers to encourage more blooms.
Light and Water
Plant hortensia hydrangea where it receives morning sunlight and afternoon shade. The harsh afternoon sun causes hydrangeas to quickly wilt and lose their flowers. Hydrangeas have shallow roots so they need frequent watering. Keep hydrangeas moist but not soggy. Hydrangeas need adequate drainage to avoid diseases. Hortensia hydrangeas planted in containers require more frequent watering than those planted in ground. Don't allow container hydrangeas to sit in a tray of water.
Soil and Fertilizing
Hortensia hydrangea prefers rich, fertile soil that is loose and well-draining. The pH of the soil affects the colour of the flowers, although changing the colour of hydrangea flowers can take several seasons to complete. An acidic soil pH, between 5 and 5.5, produces blue flowers. More alkaline soil, with a pH above 6, produces pink flowers. To make soil more acidic, add aluminium sulphate or sulphur. To make soil more alkaline, add lime. When increasing the soil pH, the iron level decreases, making the hydrangea susceptible to iron chlorosis. Iron chlorosis causes yellowing of the leaves. Apply chelated iron to solve the problem. Fertilise hydrangeas in early spring. Apply a granulated balanced fertiliser, and water in thoroughly.
Pests and Diseases
Proper growing conditions play a big part in keeping hortensia hydrangeas free of pests and diseases. Powdery mildew may occur, which shows up as greyish powdery film on the leaves. Leaf spot may also be a problem. For powdery mildew and leaf spot, ensure that the shrub is receiving adequate drainage and air circulation. Remove affected plant areas and use a copper fungicide or Bordeaux mix to prevent the diseases from spreading. Spider mites are minute reddish-brown pests that spin fine webbing in between the leaves. They suck the hydrangea plant's juices, causing yellowing or mottled leaves. Aphids are also small various coloured insects that cause the same type of damage. Both pests are knocked off the shrub by a hard stream of water or killed by insecticidal soaps.