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How to tackle overbearing hedges, according to expert Helen Yemm 

Hedges and shrubs can soon take over a garden
Hedges and shrubs can soon take over a garden Credit: Yola Watrucka / Alamy 

Every week, Telegraph gardening expert Helen Yemm gives tips and advice on all your gardening problems whether at home or on your allotment. If you've got a question, see below for how to contact her. 

How to live with overbearing hedges and trees

Two readers with related problems here: Lynn Simpson’s description and pictures of her front garden told a depressing story. The garden, she says, is “barren”: small, sloping, north-facing, open to the road. A large part of it is overhung by a neighbour’s wide (but thankfully not tall) leylandii hedge.

Lynn should reduce the conifer overhang straight away, taking care not to cut into old wood (from which it would not resprout). Then, bearing in mind the site’s limitations and that maintenance of an open front garden is not an altogether enjoyable experience, she should adopt the “less is more” approach.

Mindful of utility supplies running, no doubt somewhere under the garden, she could plant a light-canopied blossom tree in the grass somewhere near the road on the garden’s outer, lighter edge.

An amelanchier for example, a rowan, a hawthorn, or crab apple would fit the bill. Then Lynn could make a little planted patch of shade-tolerant lovelies that could cope with the challenge, such as hellebores, ferns, hostas or Japanese anemones, to extend outwards from around the tree.

Graham Bruce’s shrubby garden is dominated on one side by the dense, cantilevering growth of a vigorous, fairly youthful “pine tree” (variety unclear from his picture) that has started to ruin the lawn beneath. Can he prune it back and, if so, when, he asks? Yes, and now is the quick response.

A better course of action than just trimming the whole thing would involve cutting the lower branches back to the trunk to make it into a proper tree, thus instantly allowing more light and rain to reach the grass beneath.

Following this up with restorative pruning/shaping/feeding of the adjacent, mostly evergreen, shrubs and a bit of lawn TLC could transform the whole area, I feel.

Leatherjackets on the lawn

Our son’s lawn, his pride and joy, is being dug up by birds, possibly to feast on insects. Have you any advice?

Matt and Claire Grimes – via email

The birds are probably homing in on an infestation of leatherjackets, the brown, soil-dwelling, grass-root-eating larvae of crane flies.

The eggs were laid by the gangly flies late last summer, and the relatively mild weather will have allowed the young leatherjackets to continue feeding and growing all winter, hence the attention of hungry birds. There is no longer a chemical treatment for leatherjackets available to gardeners, so your son will have to use a biological control. This takes the form of a pathogenic nematode, Steinernema feltiae, which you water on the turf when the soil temperature is a minimum of 12C.

While he may have missed the boat for this crop of leatherjackets, he should apply the nematodes next August or September to nobble the next batch. The nematodes enter the bodies of the leatherjackets and infect them with a fatal bacterial disease. Buy Nemasys Leatherjacket Killer from greengardener.co.uk.

Hungry caterpillars

I have been putting safe (ferric phosphate) slug pellets around my hollyhocks to deal with whatever has been making the young leaves look ragged. I then found what I suspect is the real culprit, a solitary bright-green caterpillar hiding among the leaf stalks. This was in February. Is this normal?

Janet Booth – via email

It is quite normal if, as I suspect, it was an angle shades caterpillar, of a large, brownish moth, more common in the south of England than the north.

These caterpillars are often to be found in winter among the juicer shoots of various shrubs and perennials that maintain a bit of foliage. In my garden, I sometimes find them munching at the rosettes of grey foliage on my perennial stocks. They pupate just below the soil or in leaf-litter even in winter and hatch out in spring and summer.

In our more insect-aware times, we are advised, rather preciously, to “hand pick” caterpillars (and then what? Give them a severe talking to?).

In my experience, plants recover from the early spring voracity of angle shades caterpillars, so I am lenient. My pet hate is the beautiful, stripy mullein moth caterpillar. I have successfully sprayed preventively with a systemic insecticide, sacrificing one plant, which remains unsprayed and gets trashed, of course.

Your columnist has no garden-friendly answer to this one.