The Zimbabwean Gardener Issue 19 Summer 2016/17 | Seite 18

hydrangeas Silwet, a wetting agent, with the fungicide before spraying, it will not only improve efficacy but it will also control red spider mite, provided good under-leaf cover is achieved when spraying. Pruning As hydrangea plants age, they need regular annual rejuvenation that may be achieved by pruning. This also presents an ideal opportunity to get rid of all non- productive wood. In our climate, pruning is usually done in late winter. The process involves removing any dead, diseased and thin, spindly, non-productive shoots. Then, in order to stimulate new, strong, vigorous shoots during the ensuing season, remove 3 to 5 of the oldest stems, cutting them back to ground level. Finally, cut back the remaining shoots by a third to a half of their length. Always make a clean cut just above a pair of buds on a stem. Changing colour Over the past several years, plant breeders have produced many colourful hydrangea varieties. Here in Zimbabwe, we are familiar with older Mophead and Lacecap varieties that vary in colour from pink to blue and all shades in between. These colours are determined by the availability of aluminium in the soil, which in turn is dependent on the pH of the soil or growing medium in a container. If the soil is acid (low pH), the flowers will be blue, and if the soil is alkaline (high pH), the flowers will be pink. So, to change the flower colour, you need to alter the pH of the soil. Pink flowers To change from acid to alkaline, add agricultural lime - about a tablespoon per square meter. Blue flowers To change from alkaline to acid, add sulphur-containing compounds such as Gypsum and mulch with pine needles and compost. However, this can be a long-term process. Avoid planting hydrangeas close to concrete walls, as lime will be leached into the soils, not giving you a true blue colour. We have had some success applying aluminium Hydrangeas love the morning sun and partial afternoon shade. 18 sulphate, 25g per 5lt water, to the root zone once a month during the growing season. Their favourite growing conditions When planting and growing hydrangeas, think about the magnificent displays of these beauties we see in Nyanga, Chimanimani and the Vumba areas. Try to emulate those conditions as closely as possible with rich compost, lots of mulch, a cool position and, of course, routine feeding. Picabella Rose Nursery Quality and expert advice, a range of ht roses, floribundas, miniatures, standards, climbers & nostalgic scented roses. Gil 0773 208 032 Gerry 0733 360 164 [email protected] Hydrangeas at Bridal Veil Falls in Chimanimani.