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NZ Gardener - 2021-10-01

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Hints & tips

KIMBOLTON

ALTERING SOIL PH The ideal pH for rhododendrons is 5.5. Most of the heavier soils in New Zealand are too alkaline and need to be acidified. The addition of sulphur is the best method because it is long-lasting. Add before planting: 1kg per 10 square metres is usually enough. The regular use of acid fertilisers does have an acidifying effect but quite often, it will not enough to rectify any major deficiency. PLANTING IN POTS Any container is suitable for growing rhododendrons – look for one about three times the volume of the plant’s existing root ball. Just take care using concrete containers: lining with polythene or painting with two coats of acrylic paint is a good idea to ensure that the lime (which has a high pH) in the concrete will not come in contact with the plant roots. Painting or lining the inside of terracotta pots also helps prevent them drying out so readily. The container must have a drainage hole and it is advisable to put about 75mm of stone or chip in the bottom before adding the potting mix. REPOTTING After two years most potted plants will need repotting. Either repot into a bigger container or just lift them out of the existing container, trim the roots, add fresh soil and fertiliser and repot. Prune any straggly branches at the same time. FERTILISING The use of a balanced fertiliser is essential. Rodney recommends the use of Cross Hills Long-Life Fertiliser for fertilising plants in containers and hanging baskets. One application in the spring is sufficient for one growing season.

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