Marin Master Gardeners
University of California
Marin Master Gardeners

Snails and slugs: how to keep these slimy invaders out of your garden

It’s a nice evening in your garden when you suddenly spot a suspicious, slimy trail and a favorite hosta full of holes. You cautiously turn over the leaf and there it is: a snail. Question is, what do you do now?

How snails got here, and why they keep showing up
Snails arrived in California in the 1850s from France, imported by gourmands with a yen for escargot. Slugs and snails are most active at night and on cloudy days, hiding in shady spots during the heat of the day. When it's cold, they hibernate, sometimes attached to trees or walls.
A snail can lay 80 eggs up to six times a year, while a slug usually produces three to 40 eggs at a time. Since they are hermaphroditic, meaning that they have both male and female reproductive organs, they do not need to find a mate in order to produce fertile eggs. These gastropods use mucus to slip along on their "stomach feet," creating the silvery trails that glow at night. Slugs and snails are similar biologically, except slugs don’t have the distinctive outer shell of snails.

Is it snail damage?
You can recognize snail and slug damage generally by the smooth-edged, irregularly shaped holes they make in leaves, flowers, or succulents. Sometimes it is difficult to differentiate damage caused by snails from damage caused by insects such as caterpillars or earwigs. The clearest way to tell is to spot the slime trail on or near the damaged plant. It is important to determine the type of creature causing the damage in order to take the proper management steps to eradicate it.

How to control snails and slugs
There are several strategies to reduce your snail and slug population. Here’s how:

1. Clean up debris where they can hide, such as under stones or wood, under low-growing branches, or in ground covers like ivy. Vegetable gardens and other snail favorites should be placed as far away as possible from typical snail hiding places.

2. Switch from sprinkler to drip irrigation to reduces the humidity in a garden. Snails love nice moist conditions, so reducing water makes the environment less hospitable.

3. Install a copper barrier. Copper foil can be applied around the tops of planting boxes, just make sure there are no snails trapped within the perimeter.

snail on citrus
4. Solarize the soil if you are concerned that there may be snail or slug eggs in the soil. To solarize soil, place a clear plastic tarp over the soil for six weeks in late June or July, and be sure to secure the perimeter entirely with bricks or other material to keep all water and air out. Caution: only do this if you have no living plants in that soil because anything under the plastic will be killed. You can also try soil solarization in winter when the soil is fallow, but it may take longer than six weeks if there is not as much sun.

5. Encourage natural predators. Luckily, snails and slugs have many natural predators. They provide meals to beetles, snakes, toads, turtles and birds. Ducks, geese and chickens find snails and slugs to be delicious treats, too, but they also like seedlings, so it can be a mixed blessing to have them tottering through the garden.

6. Hunt them down. The hunters among you can handpick snails at night using a flashlight and rubber gloves. Destroy by crushing and dispose.

7. Choose plants carefully. One of the most effective ways of controlling snails is through careful plant selection. Snails and slugs enjoy soft-leaved, herbaceous plants like basil, beans, cabbage, dahlias, delphiniums, hostas, lettuce and many other vegetables and low-growing berries like strawberries. A few soft-leaved species such as begonias, poppies, fuchsias, geraniums, impatiens and nasturtiums are resistant to snails. In general, snails dislike grasses, plants that have rigid leaves, and woody, fragrant plants like rosemary, sage, and lavender.

8. Use baits. If all else fails, you can bait for snails. The safest method is to use iron phosphate baits available at nurseries because they are safe to use around children, pets, and wildlife. Water the garden before you apply the bait in order to encourage snail activity. The bait causes the snails to stop feeding. You may miss the slime trails, but your garden will be happier.

Original article by Juliana Jensen for the Marin Independent Journal
Edited for The Leaflet by Julie McMillan
Photos courtesy of UCANR

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