Gardening: Hydrangeas take on brooding autumn hues
Hydrangeas have been showing their colourful flowers for months and are now sliding nicely into their autumn colours. The flowers deepen in colour - the pink or red ones turning to deep wine and rich magenta while the blue ones turn purple or slate-blue. These colours have a brooding intensity that make a great contrast with the yellowing of leaves and the yellow flowers of the season.
Even the shrub's own leaves can turn to lovely shades of yellow and old gold, sometimes with a flush of red-purple. In some cases this year, the leaves have fallen early because of dry weather but only on dry sandy soil. In general, it has been great year for hydrangea flowering as they got the rain during August when they needed it.
The most popular hydrangea is the mop-head type, with a rounded flower-head. The lace-cap type has gained popularity in recent years. Instead of a rounded head of sterile flowers, the lace-cap type has a ring of sterile flowers to attract pollinating insects and a central area of jewel-like small fertile flowers. The lace-caps have the advantage of holding less rainwater and not flopping down as the weighted mopheads do.
Both kinds are good indicators of soil acidity or liminess. The flowers turn blue when grown in acidic soil and turn pink or red in limy soil. If a blue-flowered plant is moved into limy soil, it will eventually turn pink. People who can grow pink hydrangeas often want blue ones, and those who have blue want pink.
Blue hydrangeas are easily turned pink by applying garden lime over the area of the plant's roots, thereby changing the soil from acidic to limy. It is more difficult to change pink to blue but it can be done by applying some sulphate of iron and a good mulch of conifer needles and topping it up.
This species of hydrangea is native to Japan, where it thrives near the coast, and it does best here when also planted near the coast. It is not completely hardy as frost can kill the flower buds at the tips of the young shoots. Plants grown in cold places inland often fail to flower reliably.
But incorrect pruning can result in the flowering buds being pruned away. When the bush has reached a satisfactory size, to keep it from getting too big, prune in spring, removing one shoot in five each year. They flower best where they get some sunshine and in fertile soil, not too rich or too poor.