A trap plant—also known as a trap crop or a sacrificial crop—is a plant that you grow specifically to attract and feed pests (insects, mammals, mollusks, etc.), drawing them away from the plants you want to protect. Trap plants can be used, among other things, in the fight against slugs, one of the most important pests of both edible and ornamental gardens.
Slugs tend to prefer plants with soft, thin, tender leaves. That’s why they do so much damage to seedlings: the leaves of seedlings have not yet developed their adult texture, usually considerably tougher. They’ll often quite ignore the mature leaves of the same plants they devoured so voraciously when they were seedlings.
However, there are plants slugs particularly like at all stages of their growth and that can be used to divert them from other plants. Chervil (Anthriscus cerefolium) and red clover (Trifolium pratense) are two plants often used this way in organic gardening, but you’ll find more potential slug trap plants in the following list.
Best Slug Trap Plants
- Basil (Ocimum basilicum) zones 10–11
- Bean (Phaseolum, Vicia spp. and Vigna spp.) vegetable
- Begonia, Tuberous (Begoniax tuberhybrida) zones 10–12
- Cabbage (Brassica oleracea) vegetable
- Canna (Zantedeschia) zones 8-12
- Chervil (Anthriscus cerefolium) annual
- Coleus (Coleus scutellarioides) annual
- Corn (Zea mays) vegetable (seedlings only)
- Dahlia (Dahlia) zones 8–12
- Delphinium (Delphinium) zones 3–9
- Hosta (Hosta) (thin-leaved varieties) zones 3–9
- Lettuce, leaf, crisphead and Boston* (Lactuca sativa) vegetable
- Ligularia (Ligularia) zones 3–9
- Lily-of-the-valley (Convallaria majus) zones 2–7
- Marigold (Tagetes) annual
- Mustard (Brassica) vegetable, herb
- Potato (Solanum tuberosum)vegetable (some varieties are slug resistant)
- Primrose (Primula) zones 3–9
- Red clover (Trifolium pratense), zones 3–9
- Seedlings of most vegetables
- Soybean (Glycine max) vegetable
*Slugs usually ignore lettuce with tougher leaves, like Romaine lettuce.
Using Trap Plants
Often, in companion gardening, you’ll hear the recommendation to simply insert a few trap plants throughout the main crop. While that can be effective in the case of certain insect pests that don’t tend to move from plant to plant and therefore stay on the trap plant, such as aphids, this will not work with slugs, whose modus operandi is to spend the day hiding at the base of their favorite food plant and then to spread out and plunder other plants at night.
It’s more effective to plant trap plants in a row on the edge of the vegetable garden, followed by a few rows of vegetables less attractive to slugs (you’ll find a list of plants that slugs don’t like here: Slug Resistant Plants), before daring to plant, in the center of the vegetable bed, vegetables they adore, such as leaf lettuce or mustard. But better yet, give the trap plants their own plot at least 10 feet (3 m) away from the main garden, in order to draw slugs completely away from the plants you want to save.
Once the slugs have settled in on the trap plants, focus your slug control efforts there. Harvest manually at night wearing a headlamp, lay boards on the ground where slugs can hide during the day so you can pick them and drop them into a bowl of soapy water, put out slug bait, etc. Or pull out the trap crop on a hot, dry summer day, letting the slugs (that thrive on coolness and shade) cook in the scorching sun.
These same trap plants that work on slugs will also be effective in controlling another class of mollusk, snails (essentially, slugs with a shell) in areas where they cause problems. Note that in most of North America, snails are harmless: yes, they may clamber over your garden plants looking for algae and waste (read more about them in Don’t Crush Those Snails: They May Be Your Friends), but they don’t eat living leaves and there is no need to control them. It’s usually only very locally, where the brown garden snail (Cornu asperum, formerly Helix aspersa) has been accidentally introduced from Europe, that snails seriously harm plants. However, in many parts of the world, including Europe, there are many species of plant-eating snails and they can be even more damaging than slugs. Under such circumstances, a trap plant would be more than welcome.
Trap plants: using food to lead your enemy to its doom. There’s a certain sadistic pleasure in the concept!