There are at least 7 species of slugs that are garden pests in the UK. Most live at the surface of the soil, but the keeled slug lives underground attacking plant roots and laughing at slug pellets on the surface of the soil! The large black slug can grow up to 12cm long and out eat a small child, or at least it seems that way.
Slugs are the perennial enemy to the gardener. There are thankfully a number of effective ways to deal with them. The top 5 are environmentally friendly.
1) Encourage predators of slugs and snails into your garden. Frogs only need a damp puddle/pond to thrive. Grass snakes, hedgehogs and even birds can dramatically cut down the population of slugs.
2) Not for the fainthearted you can manually remove the slugs and squish them yourself. It can take a lot of time and you will never get them all. Lay down half a grapefruit skin with a small ‘doorway’ hole in the edge overnight and in the morning when you lift it you will notice lots of slugs underneath it.
3) Nematodes. These are just fantastic. A biological enemy to slugs. They are small parasites that bore into the slug or snail and breed. Eventually the slug will burst open and die. The released nematodes will then go on to find other hosts. Just water onto the soil. A single treatment can last for months if you can keep the soil moist to allow them to multiply, but for best results apply every 6 weeks during the growing season.
4) Beer traps. What a way to go. If I were a slug this would be the way I choose to go. Take a small margarine, yogurt or similar tub and put 2 inches of beer into it. The slugs are attracted to the beer and will fall in and drown. The big plus is that the birds get beer marinated slugs. This really does work and we saw slugs from over 1 meter away homing in on a freshly setup beer trap. Deal with the corpses daily or they can get a bit smelly.
5) Barriers. Apparently copper strips create an electrostatic shock to slugs as they try to pass over it. Alternatively a band of very fine gravel will prevent a slug from being able to pass over it.
6) Water on slug killer. Try to water it on the soil not on crops you are soon to eat. There are a wide variety available so check the labels for suitability and toxicity to pets/humans.
7) Slug pellets. It can be quite hard firing the pellets at slugs even though they move rather slowly. When I re-read the label I saw that you only have to sprinkle them on the ground! The slugs love these and will eat these instead of your precious fruit and veg plants. The downside of pellets is that these can poison the predators that live off the slugs such as birds, grass snakes and frogs.