Slugs are as destructive as they are slimy, and can wreak havoc in a garden. They chew holes in both leaves and fruit and sometimes attack new woody plants with young bark. Although you likely would prefer not to deal with them, they do benefit the ecosystem by helping to break down dead plant materials. Because they do serve a purpose, it is best to try and find ways of keeping them out of your garden without killing them, whenever possible. The key is to select the right plants to keep slugs away from certain areas while luring them to others.
Protect your plants from slugs by placing plants that repel them around the perimeter of your garden or close to plants you want to protect. Herbs work well as they will do double duty by protecting other plants from slugs and providing you with fresh herbs for the kitchen. Herbs deter slugs include:
- Annual basil (Ocimum basilicum)
- Annual fennel (Foeniculum vulgare)
- Annual parsley (Petroselinum crispum)
- Mint (Mentha spp., perennial in U.S. Department of Agriculture plant hardiness zones 3 through 10)
- Sage (Salvia officinalis, USDA zones 5 through 8)
Herbs aren't the only options, and ornamental plants can also deter slugs:
- Annual sweet alyssum (Lobularia maritima)
- Annual sunflowers (Helianthus spp.)
Common foxglove (Digitalis purpurea, USDA zones 3 through 9)
Common daisy (Bellis perennis, USDA zones 4 through 10)
Protecting your garden doesn't have to mean keeping slugs out. Another option is to choose plants that are resistant to slug damage and able to coexist with the slimy critters. Generally, plants with woody stems, scented foliage and ornamental grasses withstand slugs well. The University of California's Statewide Integrated Pest Management Program names several specific plants which can survive slugs, including the annual 'Purple Robe' cup flower (Nierembergia caerulea 'Purple Robe'), nasturtiums (Tropaeolum majus) and lavender (Lavandula spp., USDA zones 5 through 9). Geraniums (Pelargonium spp.) are also slug resistant but are only perennials in USDA zones 10 and 11. Elsewhere you can grow them as annuals.
On your next trip to the beach, gather any seaweed you find washed ashore and take it home for your garden. Though you're not going to plant it, you can use the salt in seaweed as a slug deterrent. As an added bonus, seaweed withers and becomes rough as it dries out, creating a gritty surface that soft slugs will avoid crawling over. To use seaweed, spread a layer of it 3 to 4 inches thick around your garden -- it will shrink to a depth of about 1 inch when it dries out. This is completely organic and safe, but remember that your plants may not like salt either. Make sure the seaweed you spread is not pushed up against plant stems.
If you have many slugs in your garden, it's often simply easier to peacefully live with them than to eradicate them. A good way to do this is to plant a patch of red clover (Trifolium pratense) near your garden. This short-lived perennial will grow in USDA zones 4 through 13. As a wildflower, it is easy to grow and slugs love it. Planting it near your garden should attract most of the slugs to the clover rather than the vegetables and flowers you want to preserve. Consider planting the clover in a container to keep it where you want it and control its prolific spreading ability.