How do I deal with slugs in greenhouses

Slugs can wreak havoc in the smallest garden or greenhouse. Basically, anywhere that you choose to grow tender, juicy young plants is a magnet for these pests and  keeping them under control is a process of constant vigilance and integrated pest management.

In the greenhouse it’s slightly easier if you can isolate the greenhouse from the outside, but slugs and snails have an uncanny habit of find their way inside and if you have any greenhouse gaps, or indeed a greenhouse border then access is always possible.

It’s not just adult slugs and snails that will wend their way into your greenhouse, bear in mind that anything you import into the greenhouse may harbour eggs, baby slugs and snails or even adults. Don’t forget that slugs can burrow and are often found between the flower pot and the plant root ball where they shelter in the daytime and reappear at night or when it is safe to come out.

The best way to deal with slugs in a greenhouse is to move everything out and wash out the whole greenhouse with a greenhouse disinfectant. Wash all the pots, trays and containers and your greenhouse benches, staging and shelving, removing any pest eggs and potential hiding place. Replace capillary matting and look inside self-watering trays, watering cans and anywhere dark and moist. If you have a greenhouse border then dig as much of the soil out as possible and replace with fresh, clean, bagged multipurpose compost. Be very wary of using up bags of old compost, slugs and snails have a very crafty knack of hiding within the plastic compost bags.

You will never get rid of them all and when you import plants into the greenhouse for over wintering for winter, or indeed open the greenhouse for summer ventilation, the slugs and snails will find a way in.

Once you’ve got the problem under control you need to be extremely vigilant. Watch out for the tell tale slivery tracks and also munched leaves, slugs and snails tend to chew large holes on the edges of leaves. If you’ve got obvious round holes within the leaves then check for caterpillars.

A greenhouse visit by torchlight is well worth the effort. Any slugs and snails lurking in nooks and crannies are more likely to put in an appearance at night and can be found blatantly feeding on plants in the dark. All you need to do is to pick them off and take them outside. Of course if they have laid eggs in the compost of your plants you will need to vigilant for some time.

Slugs and snails have an aversion to copper. Some gardeners swear by using copper tools to prevent these pests moving through the soil. Others use copper bands, copper paint and copper mats as barriers to protect susceptible plants.

Use beer traps designed for hard surfaces on greenhouse benches and greenhouse paths, these will attract some of the pests.

Create barriers made from sharp gritty materials, copper or a dedicated slug barrier, at least in the greenhouse these are less likely to be affected by rainfall but do be careful of washing them off.

Place decoy plants near those you want to protect, or use lettuce leaves, cabbage or even bowls of bran to attract them to a feast so that you can collect them up.

If you choose to use slug pellets then use them as a last resort and very sparingly. Try the organic ones first. Which? Gardening found they were as effective as the non organic and they are less of a risk to pets and children. Don’t use them in contact with leaves or plants you will eat, e.g. salads, herbs and leafy crops as they may taint the food. Keep them out of the reach of children and pets that may come into the greenhouse and clear up any dead slugs and snails as soon as you see them to prevent them entering the food chain.


Alan Jackson

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