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How to make a new border and tips on viburnum beetle, by garden expert Helen Yemm

Planting a new border
Planting a new border Credit: GAP Photos

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

How do I make a new border without damaging spring bulbs?

I want to create a new border in what is lawn and rough grass within which are many spring bulbs. Will the cutting and lifting of the turf (with a mechanical turf cutter/lifter) damage the bulbs? If it can be achieved, when would be the best time to do it?

Victoria Symon – via email

A tricky one, this. Survival of the dormant bulbs rather depends on how deeply they are embedded in the ground, I feel. I suspect that the daffodils will be far down enough to largely miss the activities of the mechanical turf cutter/lifter, whereas snowdrops, crocuses and so on may be fairly shallow and run the risk of being cut to bits, or at best seriously disturbed.

Presumably you are planning to dig the new border out (once the turf has been removed), by hand which will give you a chance to quickly relocate any surviving bulbs you encounter, as well as enabling you to trench-dig and as you do so, to add organic matter and bone meal into the ground for the future well-being of your plants.

Have you thought of using the removed turf and its population of worms, upside down, at the bottom of spade’s-depth trenches, where it will rot down and enrich the border soil for years? This is what I have always done – and recommended to others here and elsewhere. The satisfaction and results outweigh the arduousness of the job.

Whatever method you choose, it is probably best to start the job sooner rather than later, since some spring-flowering bulbs start coming out of dormancy surprisingly early, producing their first little roots as early as September. And creative gardening is much more fun and much less hard as the days shorten, but the last rays of the summer still warm your back as you work.

How to beat viburnum beetle

Our Viburnum tinus is being attacked by viburnum beetle and we have taken the advice of our local garden centre to cut back its lower branches. This seems to work in so far as the bush has put on new growth, but yet again this year I found tiny caterpillars at work (which I picked off by hand). Is there anything else I can do, without using chemicals?

Irene Dachtler – via email

Viburnum beetle larvae at work

Viburnum beetles lay eggs in holes cut into the bark of the shrub’s older branches. Eggs overwinter, larvae hatch in spring and by mid-May start to feast on the shrub’s bright new foliage, disfiguring it with tiny holes. In June the larvae move down into the soil under the shrub to pupate.

Removing low branches in which the beetles lay their eggs is one way to stall their activities, but I think you could go further, and prune and dispose of the young shoots (i.e. larvae fodder) in early May, about a month after the shrub has finished its main flowering flush. The shrub will have plenty of time to make flower buds for the following winter in the growth made subsequently.

This is how I tackle the problem of viburnum beetle, and it works to an acceptable degree. Also, in late summer I fork over the soil under the bush to disrupt things before top dressing it with what I hope is a deeply impenetrable mulch.

Galls and strange growths on trees

Hawk-eyed Daphne Frost is concerned about some oddities she has observed on young shoots of an oak sapling in her garden – shiny, lumpen green swellings that appeared, on close inspection, to be smothering many of its acorns. Is it a sign of a nasty disease that will spread, she asks?

No, these are common knopper galls, and are the work of a harmless wasp that first appeared on our native oaks about 50 years ago. There was a flurry of concern among tree boffins: would their spread mean that our oaks would not be able to make viable acorns?

But although the wasp has now spread as far as Scotland it has had little detrimental effect and seems to have merely joined the harmless community of tinies minding their own business up in our trees.

Next on the Thorny Problems reassurance agenda are the observations of Rod Kenton, who saw some strange tangled growths in the birch tree above his head “quite like wood pigeon nests, but more organised”, is how he described them. Another thing to worry about?

No. They are, in science-speak, “virescences”, deformities caused by various microorganisms, fungal, viral or bacterial and occasionally by insect activity, aka “witches brooms”, which sounds vague enough for us not to ask more questions, but apparently they do not affect tree growth to any major degree.