Hydrangea Growing Guide

Hydrangeas would have to be one of the most recognisable plants in the world. Many of the 70 or so species come from China, Japan or Korea. The most popular species is H.macrophylla (meaning big leaf) of which there are about 600 cultivars! While we think of the whole massed head as ‘the flower’, this is actually a massed grouping of colourful sepals; if you look closely you’ll see the tiny flowers in the middle of each arrangement of sepals

The lesser grown Oak-leaf Hydrangea (H.quercifolia) requires the same conditions and, with its erect panicles of white flowers ageing to light pink, is an elegant shrub.

Contrary to popular belief, hydrangeas will grow in full sun if they’re watered when they ask for it! Like silverbeet, hydrangeas wilt when they’re thirsty.

Cultivation

Hydrangeas will grow in cool to subtropical climates.
They are tough plants that cope with wind, frost and coastal conditions.
For best results, grow hydrangeas in a partly-shaded spot; however they will cope with full sun in the morning.
Hydrangeas need regular watering over the warmer months, and will wilt when parched. Deeply soak plants growing in the ground every week, and those in pots every couple of days.
Mulch well as their fibrous roots are close to the surface.

Soil

Hydrangeas are adaptable, but need something along the lines of a moist, humus-rich, well-drained soil.
Blue or pink? If you don’t know the pH of your soil, you could conduct a pH test or plant a hydrangea! In acidic soils (under 5, and often found in mountainous regions) hydrangea sepals are blue, but as the pH climbs, sepals turn mauve, pink and eventually red. This is due to the aluminium present in the soil, which is usually insoluble, but acidity increases its availability to plants.
People with blue hydrangeas often want pink and those with pink yearn for blue (just like people with curly hair who want to go straight and vice-versa!). Luckily, there’s a solution: a blueing tonic (aluminium sulphate) can be added to alkaline soil in autumn and spring to change sepals to blue, while a cup of lime (calcium carbonate) in spring will do the reverse. This needs repeating every few weeks. An easier way to have the colour of your choice is to grow in containers using the appropriate potting mix along with blueing or pinking agent. A white flowering hydrangea will remain white regardless of your soil pH.

Pruning

Prune hydrangeas in early autumn, unless there’s risk of frost, in which case prune in spring???
Reduce stems that have flowered, cutting a few nodes back down the stem. Don’t prune stems that haven’t yet flowered as these will do so the following season.

Fertilising

Feed with a complete fertiliser at the beginning of winter.
Apply Seasol and Powerfeed regularly to keep plants healthy and performing at their best.