One reason it’s so difficult to get rid of slugs is because they are hermaphrodites, which means they contain both male and female organs. Not only that, but they may alternate sexes at different times during their adulthood. Self fertilization is also possible, so if just one slug gets into your greenhouse, you will have an infestation in a very short time.
Slugs do have a purpose in that they eat dead and decaying debris in your garden, the problem is, they will also eat your plants, fruit and anything else they can reach; and slugs can climb up anything. Slugs look a lot like another garden pest, the garden snail, the difference being that snails have a shell on their back and slugs do not.
There are several ways to deter slugs, but as mentioned above, due to their extraordinary reproductive system, it is impossible to get rid of them completely. All you can do is slow down their numbers a bit.
Beer Traps: Almost every gardener has heard of using beer traps to diminish slugs; and it does work. Poor some beer in a shallow dish that is half buried in the soil around the plants they are devouring. They will crawl up the side of the dish and drown in the beer. Slugs are very attracted to beer. Once the beer trap gets too contaminated with dead slugs, dump it out. WARNING: be sure to dump it where other pets, especially dogs, can’t find it. They will eat the slugs and slugs can make pets sick.
Diatomaceous Earth: Is a powder you can find in most garden centers. It is considered safe to use around pets and on plants you will eat. It is made from crushed shells of crustaceans which cut the skin of the slugs when they crawl over it. Sprinkle it generously around plants you don’t want slugs to crawl up. You will have to replenish it every time you water.
Grass or Hay Mulch Works Very Well and Benefits Plants too: If you have a strawberry bed and the berries are being eaten by slugs, try putting grass clippings around all the strawberry plants making sure any berries are sitting on top of the clipping. Slugs don’t like decaying grass clippings because they create ammonia gas, but plants love it. Just be sure to replace the clipping with fresh ones when the old ones turn brown and are decomposed.