Every month, Garden Answers quite literally brings you the answers to your gardening questions. Write in to the team and we will give you expert information and advice about any queries you have. Here we bring you the top 10 Q&As featured in Garden Answers.
Q. Why didn’t my philadelphus flower this year?
A. Philadelphus (mock orange) are early-flowering shrubs, which bloom on new growth produced the previous summer, so it’s likely that you pruned your plant at the wrong time and cut out all the flowering stems. Straight after they finish blooming – around June time – cut back the stems that have just flowered by about two-thirds. Then they’ll put on new stems that will bloom the next year.
Q. Can I prune a magnolia?
A. Magnolias generally don’t require pruning because they naturally form a well-branched framework. However, if your plant is becoming too vigorous or there are crossing or wayward stems, you can lightly prune in late summer. Use sharp loppers and, after pruning, feed your tree and place a thick mulch around – but not touching – the trunk.
Q. What are these furry white things on my hydrangea?
A. The mass of white fluff on your hydrangeas is hydrangea scale – a sap-sucking insect that often attacks plants that are dry or stressed. It is not easy to control without chemicals and the best time to spray is in summer when the young scale are crawling around the plants. Organic sprays, such as pyrethrum, fatty acids or plant oils, are suitable, provided that you cover the entire plant including the leaf undersides.
Q. How do I prevent slug and snail damage without chemicals?
A. None of the following guarantees success, but these methods are worth a try. Spray the leaves of susceptible plants with a garlic solution – boil one head of garlic in 1L water and dilute the cooled solution with plain water at a rate of 1:10; place copper tape around pot rims; pick slugs off by hand, by torchlight; sprinkle crushed egg shells or gravel around plants; place orange or melon skin traps or trays of beer between plants and empty each morning.
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Q. How do I stop my rose getting blackspot?
A. This fungal disease infects the leaves and reduces the vigour of the plant. Make sure you pick up any infected leaves lying on the soil or remaining on the plant in autumn. Keep plants growing well – prune hard in January and feed with a rose fertiliser. Early in the year, a preventative spray of a fungicide labelled for the control of rose black spot will certainly help, but organic gardeners might need to replace susceptible plants with resistant cultivars such as white double ‘Claire Austin’ or deep pink ‘Princess Anne’.
Q. Could I plant lilies in a pot?
A. Lilies grow well in a large pot with drainage holes and a few stones placed in the bottom to improve drainage. Plant bulbs from autumn to spring into John Innes No3 or other good-quality potting compost with some controlled-release fertiliser granules. Overwinter in a cool but frost-free place, such as a cold greenhouse or porch, and keep compost moist but not wet. Move the pot into a sunny spot in spring and give a tomato feed fortnightly in summer.
Q. My box hedge is looking very sickly. What is a good replacement?
A. Box blight is a growing problem in the UK, causing leaves and stems to die back. Alternative dense-leaved hedging plants include Berberis thunbergii ‘Atropurpurea Nana’ (purplish-red, spiny, deciduous stems), Euonymus fortunei (variegated evergreen), Lonicera nitida (dark evergreen), Osmanthus delavayi (white-flowered, dark evergreen), Ilex crenata (evergreen Japanese holly) or Taxus baccata (dark evergreen yew).
Q. When do I repot my Christmas cactus?
A After Christmas cactus finish flowering, it’s good to give them a rest, so reduce watering in spring until they almost start to shrivel. Then, in June, soak the plant and repot into houseplant compost and water and feed them well so they put on lots of growth, ready to bloom at Christmas.
Q. What causes plums to go rotten on the tree?
A. Brown rot is a common problem when plums are pecked by birds or nibbled by wasps and fungal spores are able to enter and infect the damaged fruits. The disease rapidly spreads through touching fruits, so it’s best to thin the plums in summer so they are well spaced. Pick off affected fruits and clear up any that have fallen and water plants in dry spells to help prevent fruits from splitting.
Q. Will any climbers grow on a north-facing wall?
A. The following plants will thrive in the shade of a north-facing wall: Garrya elliptica ‘James Roof’ an evergreen wall shrub with glossy, wavy-edged leaves and long, silvery catkins Dec–Feb; Lonicera japonica ‘Halliana’ a semi-evergreen honeysuckle with white and yellow highly scented flowers Apr–Aug; Hydrangea anomala petiolaris a deciduous climber with white lacy flowers Jun–Aug; climbing rose ‘Albéric Barbier’ with white double flowers Jun–Jul.
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