Hartley Magazine

All the latest news, hints, tips and advice from our experts

How to deal with slugs in the greenhouse

Green-fingered gardening enthusiasts have many problems to deal with, not least of which is unwanted wildlife encroaching on their plants.

Needless to say, something like a slug tear through your flowers, fruit and vegetables is undesirable, although they can also cause damage in less direct ways – such as by consuming nutrients and limiting a plant's chances of healthy growth.

Gardeners can rest assured there is a very wide range of solutions to this issue, although none are steadfast rules that guarantee success.

In an article for online garden planner GrowVeg.com, organic grower and founder of the site Jeremy Dore suggested the use of barriers. This could be particularly beneficial for those who have found slugs to be a problem in their greenhouse.

He explained that making a moat of gritty substances around the points of entry should act as a deterrent. Copper rings are a useful solution, as they produce a slight electric shock in gastropods.

Plastic barriers made from yoghurt pots are also a useful solution – although Mr Dore added that slugs always seem to work out how to get around them in his greenhouse.

Those who have an open greenhouse could bear in mind the positive impact of birds and frogs. While birds in particular can present a different kind of problem for individuals who are growing fruit, they are great at finding and eating slugs. Frogs are also effective – especially if there is a nearby pond area for them to thrive in.

Mr Dore also recommended the use of beer, as slugs will drink themselves to death if this is left in a trap for them.

Indeed, in an article on TwinCities.com, Everyday Cheapskate columnist Mary Hunt offered much the same advice. She explained that a good method of trapping the creatures is to sink aluminium pie plants – or a similar shallow dish – into the soil, making sure that the rim is flush with the ground. Once this is filled with beer, all that is required of the gardener is to wait.

Bob Sherman, chief horticultural officer at the UK organic growing charity Garden Organic, told Friends of the Earth that this method can create additional problems of its own.

"Unfortunately these [traps] also drown beetles and other beneficial creatures," he explained, adding: "Raising the lip above the soil surface by one cm reduces this risk."

The expert continued by stating that his preferred method involves using nematodes – microscopic parasitic worms. They can be watered on to soil warmed to a temperature of six degrees. In wet weather, they will hunt down and destroy the slugs that reside under the soil.

Mr Sherman specified which slugs pose the biggest threat to gardeners: "The ones to worry about are black slugs known as keeled slugs and the grey and brown field slugs that you find all over the garden at night, especially after or during rain."

"There are no food plants I can think of that are immune to slugs and snails," the expert remarked, adding: "What you might notice, however, is that in a row of, say, broad beans, one plant will have been visited again and again and eaten down while others nearby are barely touched."

He explained that this is because of the presence of natural deterrents that can protect your growths.

"Plants are not defenceless," Mr Sherman explained. "They are responding to the chemical signals given off by the attacked plant and releasing toxins to keep the slugs and snails away."

The expert went on to suggest that the best protection is to assume that there will be some casualties when planting and sowing, preparing more plants than are needed at this early stage.