Garden News - July Digital Sampler

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The Problem SOLVER Yellowing leaves and dieback is a sign of downy mildew Why are buds rotting? Why are the flower Q buds on my Oriental poppies rotting? Sheena Allan, Stirling Oriental poppies have A large flower buds which can become water-soaked in wet weather or scorched in hot sun. This damages the bud scales, which then fail to open, a condition known as ‘balling’. The damaged tissue may then become infected with botrytis (grey mould), so Tree bumblebee using an old nesting box as a nest prompt removal is vital. Other plants with large, double flowers are also susceptible. The other possibility is downy mildew. Again, this is favoured by wet conditions. Look for mould-like growth on the underside of leaves. There are no fungicides available so cut plants hard back and dispose of the top growth. It may be wise to remove plants entirely if the new growth is infected. Can you identify the Q white-bottomed bumblebees nesting in my bird box? Linda Wilkerson, by email There are a A surprising number of bumblebees with white bottoms, but Shutterstock Sheena Allan Why won’t my containergrown fig fruit properly? Q Mandy Rye, Lincolnshire Figs need a container A at least 45cm (18in) in diameter and a potting compost of John Innes No 3 with 25 per cent added grit. Ideally, repot every three years in winter. When repotting, remove about 20 per cent of the potting compost and cut away a similar proportion of root. Figs are very drought-tolerant planted in the ground, but in a container you need to water well during the To produce fruit, figs need to be protected from frost over winter most nest in holes in banks. An exception is the tree bumblebee (Bombus hypnorum), which prefers to nest above ground and is very partial to bird boxes. It differs from the white-tailed bumblebee (B. lucorum) in having a distinctive, tawnycoloured thorax. The tree bumblebee is widespread from Asia and across Europe but is a summer, otherwise the tree will naturally jettison fruit if it dries out. Incorporate a controlledrelease fertiliser each spring and, during the growing season, feed every couple of weeks with a high potassium fertiliser, such as tomato food. Once a shoot makes five leaves, pinch out the growing tip to encourage bushy growth and the formation of embryo figs for the following year. Trees are frost tolerant but the fruit isn’t, so protect them over winter with three or four layers of fleece. new species to the UK, first found in Wiltshire in 2001, but now common throughout England and Wales. It’s active from March but colonies decline by late-July, with just the new queens hibernating over winter. Generally, as with most bumblebees, they’re pretty docile if undisturbed and very rarely sting humans. Shutterstock Can I prune my Japanese Q maple hard back? Gordon McGhie, Blyth, Northumberland These trees will usually tolerate A cutting back hard, but you should avoid such brutal treatment as it will spoil the tree’s natural elegance. When the trees are dormant and out of leaf over the winter, you can reduce the height or width by thinning out some of the longer branches. Use a pruning saw to take branches back to a well-placed, shorter side branch, at least one-third the diameter of the branch you’re cutting out. Very low branches can be taken back to the main trunk. Look to reduce the canopy by no more than a third overall. Be careful that pruning doesn’t ruin the shape of Japanese maples 48 Garden News / July 1 2017 Shutterstock
Why don’t my Q growing bag sweet peas flower? Dennis Haynes, Oxfordshire Sweet peas won’t flower if their roots are dry and overheated I wouldn’t grow A sweet peas in growing bags. Firstly, the volume of compost is very small and sweet peas hate drying out. The other reason is that in front of a south-facing wall, I suspect the roots are getting poached in the summer sun. Sweet peas do best in deep, well-cultivated soil, where their roots are cool and moist. If growing in containers, choose ones about 45cm (18in) deep and painted white to reflect the sun. Alternatively, if the containers are rectangular, line them with a polystyrene sheet, which will keep the roots cool. Even with tomatoes that tolerate warm roots, I prefer to sink some bottomless 10 litre pots into the growing bag and plant into these so there’s a larger volume of compost to hold moisture and which is also less likely to overheat. What’s killing shrubs? What are the growths Q killing my shrubs? Susan Greenwood, by email The growths are lichens. A They’re simply using the shrubs as a support and take all their sustenance from the air. They do no harm to the plants they grow on, but where they become established it’s a sign the shrub is losing vigour. Lichen can be controlled to some extent by pruning to improve air circulation and additional feeding, mulching and watering. Always mulch and prune shrubs well Dennis Haynes Alamy Quick Can you identify the leaf problem spreading through my pear tree? Baz Murray, by email The blackening of the leaves is due to the pear blister mite (Eriophyes pyri), a microscopic gall mite that feeds inside the leaf. Raised blotches start off pink or yellowish-green, but later turn black. It doesn’t affect cropping or the health of the tree, which is just as well, as there are no effective insecticides against mites. If just odd shoots are affected prune them out. How do I propagate my dendrobium orchid from the small plantlets on the stems? Margaret Hamilton, by email Under low-light levels, dendrobiums produce new plantlets, known as ‘keikis’, on the main stems. Once three or four roots form, sever the stem 2.5cm (1in) above and below the plantlet and pot into an orchid compost. Keep well watered, but out of direct sun until established. Questions Pear blister mite won’t harm your tree Is it OK to treat blue mould on my lifted bulbs with sulphur? Martin Hewitson, by email Sulphur no longer has approval for use as a fungicide. Ensure your lifted bulbs are thoroughly dried off before storing them. Remove any damaged bulbs and any displaying obvious symptoms. Store in trays in a warm, airy location until you replant. Can I save my pieris? Michael Wilson, Keighley, W Yorkshire Pieris are more droughttolerant than other ericaceous plants, but you need to increase watering to at least twice a week in summer. They’re prone to pieris lacebug attack, which bleaches the foliage, but this is associated with lots of debris and stickiness on the underside of leaves. Baz Murray Why are my plum Q leaves curling? Donald Parkes, West Midlands The damage is due to the A plum leaf-curling aphid (Brachycaudus helichrysi), a sapsucking insect that feeds on the foliage of many prunus species. It’s active from April through to late May and will have left trees by now. You can simply prune back badly distorted shoots. To avoid it next year, use a winter wash or approved insecticide for fruit as the leaf buds are opening. It’s worth examining the underside of the other leaves carefully, however, as you may also see whitishgreen insects which are mealy plum aphid (Hyalopterus pruni). These are active right into late summer, when dense colonies may develop, so a timely spray may help. Never spray any fruit tree when in flower due to the danger to beneficial pollinating insects. Damage to plum caused by leafcurling aphid Subscribe for just £1 an issue. Go to www.greatmagazines.co.uk/gn Alamy Have a chat with our gardening experts... We’ll solve your problems if you call 01733 468835 from noon-1pm Monday-Friday. Calls are charged at UK national rate. Email gn.letters@bauermedia.co.uk. Please include your full name and address. Social Post your question at facebook.com/ GardenNewsOfficial. Tweet your question at twitter.com/ GardenNewsMag. Write to Problem Solver Garden News, Media House, Peterborough Business Park, Lynch Wood, Peterborough PE2 6EA. Enclose an sae July 1 2017 / Garden News 49
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