Anna Pavord's A to Z of pests and problems: P is for passageways, pests and pruning

Our green-fingered correspondent Anna Pavord continues her A-Z of horticultural pests and problems standing between you and your perfect garden

Passageways

Urban gardeners often have to cope with a narrow return at the side of a terraced house, made longer than it was originally by a kitchen extension. With high walls either side, this can be a dark, rather uninviting space, but it may at least provide access to the garden at the back. Whether you are hauling garden rubbish out to the tip or hauling mushroom compost in to improve the soil, this is an invaluable asset.

If it’s regularly used for access, you may not want to clutter up the passage with plants. But if you don’t, there is garden potential even in this unpromising area. Ferns in pots, for instance, will probably do better in the dark, cool environs of a passageway than they do in the dry, thin soil of the average town garden. Their foliage will soften the surroundings of brick and concrete, and provided you remember to water them, they will need very little regular attention.

Try one of the elegant maidenhair ferns, such as Adiantum venustum, a native of China and the Himalayas. It produces very beautiful, lacy fronds, rarely more than 15cm/6in tall in a bright lively green. This is an evergreen, but if you remember to shear down the old fronds in late winter, you’ll have the extra pleasure of watching the new fronds unfurl in a surprising, bright shrimp pink.

Peach leaf curl

This is most likely to affect peaches growing outside. I learnt to live with the problem, though there’s no doubt it has a debilitating effect upon the tree. I made up for that by pressing upon it food and drink, like building up a child after the flu. The disease affects all the first leaves which blister hideously and then drop off. But the subsequent foliage is usually clean and it stays clean all season.

There is a theory that planting garlic round the base of the tree keeps leaf curl at bay. Not in our garden it didn’t, and I’ve get to meet anyone who swears that this works.

But it’s no crazier than the old belief that if you carved an inscription on a peach stone and planted it, all the peaches on the tree that subsequently grew would have the same inscription on its stones. Ralph Austen banged that superstition (and others) on the head in his Treatise of Fruit Trees (1653).

Rain is the bearer of peach leaf curl, which is why trees grown under glass so rarely suffer from the problem. It is not the rain itself that matters but the fact that it carries the fungal spores (Taphrina deformans) that cause the disease.

You can sometimes check it by spraying with fungicide, but this is a preventative treatment rather than a cure. The first spray must be in autumn, just before leaf fall. Than you must do another two sprays in early spring, before the blossom comes out. I never did spray, but only because spraying – any spraying – is the most tedious and unfulfilling job in the gardener’s canon.

In old kitchen gardens, you notice that there is often an overhang of stone at the top of the wall to keep trees, as well as wall dry. This is the best defence against peach leaf curl. You can make your own temporary shelter of wood and polythene to keep off rain during the critical period in the first four months of the year. This is likely to be more effective than using fungicides. But you must roll up the polythene in good weather at blossom time so that pollinating insects can do their work.

Pests

Novice gardeners will probably get the idea from gardening books that there are an awful lot of them: mangold fly, mustard beetle, pea moth, rhododendron sawfly, gall mites, leaf blotch eelworm and the like. In a mixed garden, however, there is little likelihood that you will be wiped out byf any of the above. Bugs exist to feed other creatures. If you wipe them out with insecticide, the predators will go, hungry, elsewhere. Then when the pests come back, they won’t have any competition. Aphids are the most common pests, especially the greenfly that congregate on roses. If you cannot bear to wait for order to reassert itself, spray with an insecticide, but choose one that is specific to the job in hand.

Phytophthora

This is not a word you want to have to say too often. Nor do you want to contemplate the dire picture of a country stripped of the native trees that we have for so long taken for granted. The P-word is now horribly common, and can kill azaleas and rhododendrons, Lawson cypress, heathers, apple trees, ornamental cherries and sweet chestnuts. There are many different kinds (potato and tomato blight are caused by phytophthora pathogens), but the one we hear most about is P. ramorum (sudden oak death). This was first identified in the US in the mid-Nineties but was already in the UK by 2002. Its first victims were rhododendrons, viburnums and camellias, but more serious is the potential effect on oak trees. At present there is no cure available to gardeners. Foresters put their faith in the possibility of seedlings emerging with natural resistance to the disease. But that’s what they hoped would happen with the elm too. And we’re still waiting…

Pruning

Plants present many of the same characteristics as children. The intense period of bringing them on, worrying about the right food and so on, is followed by an equally intense period of trying to rein them in. There’s no equivalent to pruning in childcare, but gardeners have this one enormous advantage over parents.

Good pruning is a matter of working with, rather than against a plant. The most important thing, before you make any cuts, is to have clearly in your mind the essential qualities of the plant you are about to attack. Don’t reduce them all to the same bun-shaped blobs. In the most general terms, shrubs that flower in the first half of the year do so on growth made the previous year. These can be pruned after flowering. Shrubs that flower in the second half of the year bear the flowers on the new wood they have made in the first half. These are best left until early spring.

Pruning kicks a shrub into top growing gear. “Crumbs,” it says to itself. “Someone’s trying to do me in”, and it pumps energy into dormant growth buds lying along its stems to replace what it feels it has lost.

If you pruned a late summer-flowering buddleia or caryopteris when it had just finished flowering, the resultant tender new growths would coincide fatally with the first frosts. So you leave them until February before pruning. Rambling roses are best dealt with when they finish flowering. Hybrid Tea roses (both bush and climbing) are best left until February.

Now and again, it pays to take out a stem completely at ground level, especially when the main framework of a climbing rose has crept higher and higher up its support. This drastic reduction sometimes forces the rose to send out a new shoot from the base. A hefty mulch helps, too.

Pruning is often fuelled by fear. We feel a shrub is getting out of hand; reducing its size is the only criterion. But if we take the trouble to understand the consequences of our pruning, the results will be so much better.