Just as we begin to think about wrapping up things in the garden for the season, slugs slither out of their homes underground to lay their eggs for next year.
“What slugs want is a place that’s warm and moist,” says Claudia Groth, an Oregon State University Extension Service master gardener. “That’s why spring and fall is when they’re most active. They’ll be coming out soon to lay eggs.”
Slugs aren’t crazy about winter and summer. They bail from cold or hot weather. But fall and spring are agreeable seasons for slugs. In the perfect conditions of autumn—when the heat starts to wane and the first rains come—the mollusks lay eggs in clusters called clutches.
Eggs mature slowly over winter and hatch in spring. Those laid in spring hatch more quickly. Many slugs overwinter as full-sized critters and are ready to go in spring, showing up to scrape and shred plant leaves with tongues lined with thousands of tiny, extremely sharp teeth.
“In fall, you’re trying to kill them off before they lay eggs,” Claudia says. “In spring, when your plants are poking their heads up, you need to protect them. Once the leaves are nipped, the damage is there all summer.”
The pests are particularly fond of lettuce and other salad greens, broccoli, beans, hostas, strawberries, primroses and daffodils. Sturdier plants, such as ferns, sedums, ornamental grasses, bleeding heart, heuchera, hellebores and most herbs, fend slugs off reasonably well. Woody plants are also usually unbothered.
Because slugs go on attack at night and look for protected places during the day, you will find them under ground covers or mulches and in thickly planted perennial or annual borders.
“Many gardeners grow plants tightly in their beds to keep weeds from growing,” Claudia says. “That’s an environment that provides them with a 100% hiding place all day.”
Slugs will crawl beneath almost anything where it’s dark and moist.
“The first thing to do when starting a control program is to clean up the garden,” Claudia says. “Don’t leave things all over the yard. They can even hide under garden gloves.”
Raise pots onto bricks or pot feet. Pull mulch away from plants. Remove weeds, where the pests like to nestle down. Tidy under porches and other raised structures.
Although sanitation is the first line of defense, there are plenty of other methods for control. Get started now. Young plants are most susceptible.
Oregon State University Extension Service Master Gardener Claudia Groth recommends the following slug-prevention steps:
- Water in the morning. If you water in the evening, it’s wet until early in the morning. You’ve given slugs the best environment when they come out at night hungry.
- Put out beer traps. Use a pie plate or bury a plastic yogurt or margarine container almost to the rim. Pour in beer. Remove dead slugs daily and refill with beer.
- Don’t use salt, which can build up in the soil and damage plants.
- Get a duck, which will make a quick dinner out of slugs. Check for local restrictions first.
- Create an artificial hiding place by placing a board in slugs’ favorite places. In the morning, lift the board and remove slugs. Drop them in a bucket of soapy water.
- Go out at night with a flashlight or headlamp and handpick them.
- Use bait. There are two types. One is a synthetic bait that contains metaldehyde, which is toxic to humans and can be fatal to dogs if eaten in large amounts. The other contains iron phosphate, which is considered low in toxicity, according to the National Pesticide Information Center at OSU, but has been known to sicken dogs in high amounts. It can be used in organic vegetable gardens.
- When baiting, scatter rather than make piles or bands. If you choose the latter, slugs may go right by. If you scatter, they are likely to encounter the bait.