There is a simple way to save your spring bedding plants from slugs and snails. Start with transplants, not seeds. If your plants are already growing before slugs and snails hatch in the spring, they are more likely to survive slug and snail attacks. The problem with this approach is that if the soil is still too cold for slimy pests to emerge from their eggs, it is usually also too cold for strong spring growth. However, this approach works for frost-hardy and cold-hardy plants. When timing your plantings is not enough, there are other more and less effective ways to outsmart these pests.
- Plant seeds a little deeper in the ground and pat down the earth over them. One study found that firming up the planting bed was as effective as one application of a poison called metaldehyde for stopping slug infestations.
- If your garden goes dormant during hot, dry weather, or during winter cold, use this as a time for deep cultivation. Digging up or plowing the soil exposes slugs and snails to dry air that can kill them.
- Invite slug and snail predators into your garden. Install a bird bath. Dig a pond for frogs and toads. If you live where they are hedgehogs, leave out hedgehog fodder (but not if your garden has ripe berries or melons).
- Starve your slugs in the fall, but feed them in the spring. Most species of garden slugs prefer to eat decayed plant matter and only eat growing plants if they can’t find decayed leaves, stems, and bark. (The greedy field slug is an exception to this rule.) Leave them a little leaf matter to eat in the spring so they won’t eat your seedlings. But deprive them of dead plant matter in the fall so they won’t be able to lay eggs or prepare to hibernate in the winter.
- Let plants fight slugs for you. Slugs are repelled by the scents of artemisia, bleeding heart, chives, cornflower, fennel, forget-me-not, foxglove, fuschia, garlic, geraniums, hydrangea, lavender, nasturtium, mint, peony, pink, tulip, and wallflower. Place these plants at the edges of your planting beds to keep slugs out, but be aware that an especially hungry slug will even eat these heavily scented plants.
- Be especially aware of slugs in garden spots where you have planted cabbages or lettuce, even if you planted them last year and you are using the bed for some other kind of planting this year.
- Build a barrier of diatomaceous earth. Just dusting the ground with these powdered rocks won’t be enough. You need to have a wall about 25 mm (1 inch) tall and 75 mm (3 inches) wide to make slugs and snails turn around at the border of your flower beds and vegetable plots. Other kinds of finely crushed grit and gravel, as well as eggshells, will serve as a deterrent, as long as they are dry and mounded. Sawdust won’t work if it’s wet.
- Install copper sheets at the edge of plantings and around the trunks of trees. A vertical copper sheet needs to extend 2 inches (50 mm) below the ground and 2 inches (50 mm) above it to stop these little crawlers. Copper bands around tree trunks need about 200 mm (8 inches) of overlap to allow for the growth of the tree, and they need to be attached to the tree with a single staple so the copper band does not deform the trunk. Copper barriers can also be used to protect potted plants. Remember, you always need to make sure there are no snails or slugs inside the area you want to protect before you put up a copper barrier that would keep them inside.
- Paint Bordeaux mixture (copper and lime) all the way around the base of trees and seal with latex paint. This will deter snails from crawling up the tree for up to two years. It’s best to apply Bordeaux mixture in the winter or spring so you don’t trap snails or slugs on the tree.
- Kill slugs and snails with beneficial nematodes. These tiny parasitic worms attack and kill slugs and snails but leave other animals and people alone. Just buy the nematodes, mix with water as directed, and spray around your plants.
- Lay down anti-slug tapes at the base of larger plants. Be sure to weight down the tape with stones or gravel, but don’t create a bridge across the tape for the slug to cross. The chemicals in the tape will cause indigestion to the slug when it tries to slide over it, and it will turn around.
- Trap slugs with beer (see the instructions for slug pubs). Budweiser and Michelob have a yeastiness that appeals to slugs. Yeast and sugar water will also work if you can’t buy beer.
- Provide your slugs with their own garden Starbucks. Coffee, colas, or caffeine sprays cause slugs to become internally hyperactive in a way that freezes them in place. Their foot pulls back into their shell so they cannot move forward. High doses of caffeine cause them to become so jittery they die of muscle spasms or of dehydration if they are trapped in a dry place. It’s useful not to spray slugs with so much weak caffeine mixture that they stay hydrated. Unlike most pest control products, the stronger the product, the more you can use.
- Provide slugs with an edible hotel. Eat half a grapefruit, cut a small hole in the rind as a “door,” and place upside down in your garden. Wait a few days and then collect the slugs that gather within, throwing them into the trash or your compost bin. You can also place large lettuce or cabbage leaves on the ground to trap slugs, although this only works in cool, damp weather.
- Pick snails and slugs by hand. You will have to work at night with a flashlight, and you will have to collect the critters every night for a couple of weeks to make a substantial difference, but there are no poisons, no environmental damage, and the only expense is your time.
Alternatively kill slugs and snails with poisons
Metaldehyde, which is also known as Meta, has been used for decade as a fuel for camp fires. Campers noticed that Meta tablets discarded at a campsite killed snails and slugs. It turned out that a slug’s body metabolizes metaldehyde into acetaldehyde, which is the same chemical a human’s body makes after drinking too much. Metaldehyde makes slugs “drunk.” Their motions become uncoordinated, and they become dehydrated as they secrete large amounts of mucus. Sometimes metaldehyde kills slugs outright, but it more often just paralyzes them. To keep other animals from eating the poisoned slugs, it is best to gather stunned slugs after putting out metaldehyde and discarding them in the trash.
Metaldehyde comes in familiar blue pellets and also in aerosol sprays. The blue dye is added to the pellets to make them less noticeable and less attractive to other animals. By itself, metaldehyde smells bad and is somewhat repellent to slugs, snails, and people. The “inert” cereal ingredients in the blue tablets are added to make the pellets more palatable to the intended pests. Because the bait doesn’t completely mask the odor of metaldehyde, it’s important to scatter Meta pellets rather than piling them up. Isolated pellets kills more slugs than pellets in piles.
A much more effective chemical called methiocarb. It’s a potent neurotoxin. It’s very good for killing slugs and snails, but it also kills the animals that eat them and makes humans sick. Methiocarb is now banned for farm and garden use in the European Union, and any trace of the chemical is banned in food sold the USA. Even if you can buy this slug and snail poison, you should never use it around your home or in any place frequented by children or pets.
A kinder, gentler organic alterative to these poisons is iron (ferric) phosphate. It doesn’t kill slugs outright. It only keeps them from feeding. Ferric phosphate is approved for organic-certified farms and gardens.
And another chemical alternative for slug and snail control is glyphosate, better known as the Monsanto chemical Roundup. Glyphosate kills the weeds that feed the slugs that would otherwise be in place to eat tender shoots of vegetables and flowers. It also has a direct, toxic effect on snails. It interferes with their ability to make proteins, and slows down their growth. It stimulates the snail’s metabolism so that it “burns” amino acids as well as carbohydrates. No study has shown that glyphosate has a similar effect in humans, but many gardeners reject the product and others don’t use it around vegetables.