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Outdoor Plant of the Month – Hydrangeas
Hydrangeas are popular, perennial, garden shrubs with beautiful, delicate heads of flowers in shades of pink, white or blue. The mophead and lace-cap hydrangeas are most well-known for their ability to change colour in different soils – changing blue in acidic soil and pink in alkaline soil.
Hydrangea are native to North and South America, the Himalayas, and central and eastern Asia and thrive in the heat of the summer months, producing stunning round flower heads in mid-summer.
Hydrangeas are easy to grow, quite hardy and resistant to most pests and diseases.
With numerous varieties to choose from, you’re certain to find one that’s right for you.
Blue or Pink?
A distinguishing feature of some Hydrangeas is the ability to change colour. This is not true of all Hydrangea but most often seen in Mophead and lace-cap varieties where flower colour is determined by the pH of the soil in which they are planted in. When selecting a Hydrangea, if you have a preferred flower colour, it is important to know the pH of your soil. The soil pH affects aluminium availability, Hydrangeas with blue or pink flowers tend to be blue in acid soil conditions (high available aluminium levels), mauve in acid to neutral soil conditions, and pink in alkaline conditions (soil containing more lime).
White flowers, and also green-flowered cultivars, remain white or green regardless of soil pH.
For container grown plants it is a lot simpler to determine the flower colour as the soil can be selected to meet with your colour preference.
Secrets of Success
• To get the best flower colour, choose cultivars that give the best colours for the pH in question.
• Hydrangeas thrive in a moist, but well-drained soil, in a cool, semi-shady part of the garden. Try to avoid exposed east-facing sites, where cold winds may damage young spring growth, and also avoid dry, sunny spots.
• When planting, work plenty of organic matter into the soil prior to planting, after planting and in subsequent years apply organic matter as mulch.
• Hydrangeas can be fed with fertiliser annually in late winter or spring.
• Most pruning should be carried out in late winter or early spring. However, the climbing hydrangea is pruned after flowering in summer.
• Try to use rainwater to water hydrangeas, since mains hard water can affect the flower colour, turning blue flowers mauve or pink.
• Hydrangea Colourant can be used on plants to make the flower colour blue or intensify its natural colour. Hydrangea Colourant is available from our Garden Sundries Shop, 500g – £4.99 – Always follow manufactures instructions for use.