In many gardens, mophead hydrangeas (Hydrangea macrophylla) are the stars of summer. These super-tough deciduous shrubs have large heads of blue or pink flowers from late spring and often well into autumn. These flower heads consist of individual sterile flowers. Curiously, the flowers change colour depending on the acidity of the soil – blue and purple in acid soils, pink in alkaline soils. Plants in containers can have their flower colour changed or enhanced by adding blueing tonic to increase acidity for bluer blooms, or lime to intensify pink colouration.
As well as the mophead form, there are also lace-cap hydrangeas, which have a central cluster of fertile flowers surrounded by sterile flowers to give a lacy effect. For longer flowering, discover the newish repeat-flowering varieties, including the Endless Summer series.
Others to enjoy in cool-climate gardens include H. arborescens ‘Annabelle’, with its large heads of white flowers, and oak-leafed hydrangea (H. quercifolia), with its panicles of white flowers and large leaves that colour deep red in autumn. Hydrangeas grow well from hardwood cuttings taken in winter at the same time plants are being pruned.
Q EXACTLY WHEN AND HOW HARD SHOULD I PRUNE MY HYDRANGEAS?
Karen, Botanic Ridge, Vic
Determine what type of hydrangeas you have, as they require slightly different pruning methods. Forms of Hydrangea paniculata and H. arborescens flower on the current season’s growth, so prune any stem back to about 30cm, cutting to just above a pair of buds. Do this in winter, or, in very cold areas, early spring. H. macrophylla and H. quercifolia flower on the previous year’s stems, so should be pruned in late summer when flowering has finished. Prune stems that have flowered by at least half, and remove weak or dying stems. Leave stems that haven’t flowered yet.