Tony Dickerson problem solves
QWhat is the best way to look after my topiary box in containers?
ABox make wonderful topiary features in containers. If they’re placed in full sun, keep them well-watered in summer but avoid wetting the foliage. Box will tolerate deep shade, too. Apply a general purpose liquid feed fortnightly and, in spring, top-dress the pots with fresh potting compost and a little slow-release fertiliser, such as Vitax Q4. Repot every two years in spring, using a mix of John Innes No 3 with some added multi-purpose and sharp sand to create an open mix. If you’re unable to pot on into larger containers use an old saw to take a couple of inches off the bottom of the rootball and a few slivers down the side. Tease the roots out well and repot, adding fresh potting compost to the bottom of the container and down the side. Avoid the old advice to clip on Epsom Derby Day. This encourages soft growth that’s susceptible to box blight. Instead, do your main clipping in August. In warmer weather new growth will be tougher and more able to resist infection. Do a final clipping in early September.
Box displays a few distinctive leaf symptoms if it’s unhappy. In containers, if it’s too dry, foliage may scorch in bright sunlight. A general bronzing or orange colouration may also result if plants dry out. Yellowing to the leaf tips and margins over winter is very common and of no significance, plants quickly growing out of the problem in spring.
The two major problems of box blight and box tree caterpillar may not be avoidable, so be tooled up. Siting the containers in a sheltered spot with some overhead protection from rain may help with box blight, but I’d have a bottle of Bayer Fungus Fighter Plus handy, which is likely to be the most effective treatment.
For the caterpillar, a number of products, including those based on pyrethrum, will be effective but plants need a thorough spraying to penetrate the silk webbing the caterpillars surround themselves with.
Q What’s stunting the growth of my centaurea? Barbara Brand, Crawley, West Sussex
A Knapweeds, although they’re members of the daisy family, have some of the most attractive and distinctive flowers of any border perennial. They generally do best in well-drained soils in full sun.
I suspect the problem here is powdery mildew. This fungal disease becomes common in May and June as the weather becomes warm and dry. The fungus invades the leaves and later you may notice a white, powdery covering as spores are produced which then spreads the disease on the wind.
Keeping plants watered and growing strongly will help but you may have to resort to a fungicide. Most of the commonly available ones are approved for control of powdery mildew. Check product labels for details. Alternatively, you could try a product such as Ecofective Plant Defender, which creates a protective layer over the foliage, helping to reduce infection. In autumn cut back infected foliage and dispose of it.
Q When can I move my rhododendron? Mr A Marsh, Exeter
A Evergreen t trees and shrubs move best in spring or autumn. With those that flower in spring, such as rhododendrons and camellias, do it immediately after flowering, just before the new leaves open. It’s too late now as the transplanted shrub would struggle in warm summer conditions. You can, however, do some preparation by pruning back some of the longer growth so it moves more easily in the autumn.
Avoid chopping everything back as this will lose the flowers for next year. Choose some of the longest shoots and prune them off where there’s a good sideshoot lower down. You may also want to clear the lowest sideshoots right back to the main trunk.
Q Why are flower fading early on my new hydrangea? Lisa Longbo om, Leeds
A There are a number of possible causes for the flowers fading early and the leaves falling. Most hydrangeas enjoy cool, shaded conditions. A few are more tender and do well indoors, but you need to check the label for details as outdoor types will not last long indoors. Also check you aren’t overwatering. The potting compost should be moist, but not saturated. Finally, it’s possible the plant got chilled before you got it. On the nursery it’s likely to have been in a polytunnel but it may have spent a chilly night or two on a lorry. It may be worth chatting with the plant centre where you bought it. To gauge survival prospects, check out the roots. Healthy roots are white and quite tough. If they’re black and fall apart on being teased out, the prognosis isn’t good.
Q Was my grape vine frosted? Andrew Palle , Brentwood, Essex
A The answer, unfortunately, is yes. The night of April 26 saw a late frost across England as temperatures fell to -2C (28F).
Although not particularly cold, damage to plant cells is proportional to the speed of temperature drop and this was severe, following a warm, sunny day. The damage affected a range of ornamental plants and fruit.
The blackened buds and curled leaves on your grapevine were replicated here at Wisley, where the entire vineyard crop was lost. Pears and plums which blossom early had already set fruit, but apples were also affected. In Belgium, it’s estimated that 80 per cent of the apple crop was lost. Where plants have been frosted, prune out damaged growth to a sideshoot or bud and apply a general fertiliser, such as Growmore. Where entire plants are damaged hold off for a few weeks before doing anything as they may produce a second flush of foliage.
Q Why do my rose leaves have orange spots? Linda Whinney, Norwich
A This is rose rust. It’s a disease specific to roses so it won’t affect other plants in the garden. It’s important, however, to take early steps to control it.
Rusts have two stages in their life cycle and it’s the second stage that produces spores that overwinter to spread the disease the following season. If just a few leaves are affected pick them off and dispose of them. It’s important to gather up any fallen leaves from last year as they could be harbouring spores. In the autumn, repeat this operation.
Most modern roses are pretty resistant, so if the problem persists and shrubs fail to thrive, consider replacement. Alternatively, several of the commonly available fungicides are approved for control of rose rust. Check the product labels for details.