Gardening: Slugging it out with unwanted visitors

A slug. Picture by RHS/Andrew Halstead
A slug. Picture by RHS/Andrew Halstead

It’s a no-brainer that slugs and snails topped the Royal Horticultural Society’s (RHS) Gardening Advice Service’s top pest of the year list last year.

Unsurprisingly, honey fungus was the top disease (it has been for the last 21 years).

Honey fungus. Picture: RHS/Jenny Denton

Honey fungus. Picture: RHS/Jenny Denton

There is a north/south divide, with the south getting a host of new pests which haven’t reached us yet, such as fuchsia gall mite and thrips outdoors.

In 2015, slugs and snails, which had been the number one pests for eight out of the past 10 years, were pushed off the top spot by the box tree moth, but last year the pests were gardeners’ enemy number one again with a record number of enquiries.

Fuchsia gall mite, first detected in mainland Britain in 2007, is now widespread in southern England.

Glasshouse thrips were a greenhouse pest until 2008 when they began to be reported on outdoor shrubs, thought mainly to be in sheltered positions in warm urban areas.

Vine weevil adult. Picture by RHS/Joyce Maynard

Vine weevil adult. Picture by RHS/Joyce Maynard

Also known as thunder flies, thrips feed by sucking sap from leaves and flowers. Adults have narrow, dark brown bodies up to 2mm long with an orange-tipped abdomen.

The weather had an impact on bacterial diseases, which thrive in moist, mild conditions, securing 8th place in the table, with RHS scientists dealing with twice as many enquiries about fireblight in 2015.

Fireblight is a bacterial disease that kills the shoots of apples and pears and their ornamental relatives. Symptoms include the wilting and dying of blossoms and shoots.

Scabs were named the 9th biggest disease problem, with the RHS recording a 65 per cent increase in the number of enquiries.

Scab diseases disfigure the plants by producing unsightly dark spots on the leaves.

Blossoms and fruit can be attacked, and the vigour of the plant reduced.

Apple scab is a big problem in my garden. Other hosts affected by scab diseases include loquat, olive, pear, poplar, pyracantha, rowan, and willow.

RHS head of plant health Gerard Clover said: “Simple steps such as choosing more resistant varieties and taking an integrated approach to dealing with them, which could involve using a combination of controls together such as biological and cultural, can help gardeners fight back.”


If you’re doing that traditional Easter trip to the garden centre or nursery, make sure the annuals you buy are hardened off before you plant them out.

Half-hardy annuals like Surfinia, petunias, French marigolds and Antirrhinums can’t go outside until your last frost date, as they are tender.

It’s traditional to plant potatoes on Good Friday (mainly because it was one of the few days off pitmen got). If you got off to an early start last month with your spuds, then they may be ready for earthing up – covering the haulms (stems) with soil. Start this process as the shoots start to show, paying special attention if frosts are forecast. If frost is forecast, protect early, young potato shoots. They’ll need protection even in unheated greenhouses and tunnels, as well as outdoors. Earth them up or cover with newspaper, net curtain or horticultural fleece overnight.

Prune spring flowering shrubs such as Forsythia, Ribes (flowering currant), Kerria japonica and winter jasmine when flowering has finished. Next year’s flowers will be produced on stems growing over the coming months, so cut back hard now to get the shape you want for next spring. Wait until summer to prune magnolias such as M stellata and M. x soulangeana.

Once soil is warm and still moist, mulch well, to a depth of 6cm/3ins. Use leafmould or home-made compost if possible, to suppress weeds and help retain moisture levels right through the summer.

Start a new lawn from seed. Soil should be moist for sowing.

And once sown, seed must be kept watered in dry spells. When designing a lawn, remember that curves are much easier to mow round than sharp corners. Thicken up a lawn that has become patchy and thin. Rake all over vigorously, then scatter grass seeds where growth is thin, concentrating particularly on bare patches.

Hardy annual seeds can be sown directly into open ground, but wait until you can see weeds growing strongly before sowing.

Take cuttings from young shoots of shrubs. They should be putting on new growth now, and will root easily.

You can still plant herbaceous perennials such as Geranium, Astrantia and Oriental poppies. Check that the plants you buy have strong, green shoots and plant them into well-prepared soil.

Divide clumps of herbaceous perennials that you want to propagate, those that have become too large for their allotted space, and those that are flowering poorly or have lost their shape. Bamboos and clumps of bulbs or rhizomes can be divided in the same way. Make sure that the transplanted divisions have roots, shoots, and are given adequate water to settle into their new positions.

Prune penstemons and other slightly tender plants such as Teucrium and lavender. Make the cuts just above fresh, new shoots.

Apply a general-purpose fertiliser to borders and beds. Take care not to damage emerging shoots, or to burn them with fertiliser.

Place card collars around the stems of brassicas to prevent an attack of cabbage root fly.

Sow pots of herbs such as parsley, coriander and basil.

Cover blossoming fruit trees with sheets of fleece on frosty nights to protect embryo fruit.

Sow seeds of the following if conditions are fine: beetroot, parsnips, turnips, onions, peas and mange tout, broad beans, lettuce and salad leaves, spinach, radish, rocket, mizuna, pak choi, cauliflower, cabbage and Brussels sprouts.


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