THIS would have to be one of the most rewarding plants to grow - lovely soft, deep-green foliage contrasted with huge, brightly coloured flowers.
For a long time these beautiful plants were found mainly in old-fashioned gardens but they are now making a comeback.
Older varieties of hydrangea could grow quite tall and tended to become "leggy" if not pruned correctly but new varieties have now made them a much more versatile plant.
Hydrangea macrophylla is the most well-known species, of which there are two shapes: mopheads and lacecaps.
Mopheads are almost purely composed of sterile flowers, whereas the lacecaps have a few large flat sterile flowers around the edge of a mass of tiny true flowers.
The non-fertile flowers last a long time because they are never fertilised or produce seed.
The recently developed Endless Summer range of hydrangea produces abundant blooms on both old and new wood all summer long and never needs pruning.
Lacy, deep-pink centres of Twist-n-Shout are surrounded by gorgeous blossoms of pink or periwinkle blue, depending on soil type.
Sturdy red stems and glossy deep green leaves turn red-burgundy in autumn to offer year-round interest in the garden.
Twist-n-Shoutis an elegant stand-alone specimen, dramatic in combination with other plants, and compact enough for containers growing to about 120cm high and 120cm wide.
Hydrangea "You & Me" is another new variety that grows to only 80cm high and 1m wide, has striking double flowers and will withstand high temperatures as well as frost.
The Oak Leaf Hydrangea (Hydrangea quercifolia) is named because of its scalloped leaves, which change from green to rich crimson in autumn.
It has large creamy cones of sumptuous flowers and, like those of Hydrangea paniculata "Diamond Head", they become tinged with a rosy pink towards autumn. Hydrangea paniculata is popular for the pyramidal shape of the flower heads.
Why do the flowers change colour?
The flower colour in most hydrangeas 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 agent (containing aluminium and iron) will turn pink or mauve hydrangeas blue.
It should be applied once a month in March and April and again in August, September and October, following the directions on the pack.
A cup of lime (calcium carbonate) added to the soil in spring will cause blue or mauve hydrangeas to turn pink.
Once buds have begun to form, it is too late to change their colour. White flowering hydrangeas will remain white, regardless of soil pH.
Although the newer hydrangeas don't really need pruning, older varieties will.
In most areas hydrangeas can be pruned in March or April. Don't cut back into old grey wood.
If hydrangeas are pruned too fiercely year after year, flowering will be reduced to 10% or less, so just cut back the green, current season's growth to two plump eyes, or leaf buds.
Leave stems that have not flowered as these will flower the following season.
If you want to pick the flowers for indoor arrangements, by all means do so. That is really good for the plants.
Most garden hydrangeas are tough plants that thrive in moist, humus-rich, well-drained soil.
Plant in a position in sun or dappled shade that offers protection from the hottest sun and mulch well.
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