Where Do Garden Slugs Spend the Winter?
By Emily Selleck, Community Educator, Horticulture, Essex County

Not if Florida!

Having been the wet summer it was, I have had many calls from frustrated gardeners bothered by slugs munching their way through spring and summer gardens. Even in September, folks are were still seeing holes in lettuces and tell-tale, slimy trails in hosta beds. When asked recently where slugs spend the winter, I jocularly replied “Florida”. I hadn’t been beset with this particular garden pest this year, so perhaps I didn’t appreciate the magnitude of the problem - until I saw the crestfallen look on the questioner’s face.

Slugs often arouse the anger (not to mention frustration) of gardeners because both slugs and their damage can be so visible. Slugs aren’t entirely villains, though. Slugs and their close relatives, garden snails, do have a role in the landscape as recyclers of decaying plant material. Some species even eat aphids and small caterpillars although far more dine on tender vegetation. Slugs also eat a variety of other things - not all of them attractive - such as weeds, animal feces, and the bodies of their fallen fellows.

In the animal kingdom, slugs and snails are classified as mollusks, relatives of squid and octopus. (Let us rejoice that garden slugs are far smaller than squid!) Several different species of slugs attack garden plants, two of the most destructive species being the common gray field slug, Agriolaimax reticulatum, which varies in color from gray to brown to buff, and the large black slug in the genus Arion. In our neck of the woods, the gray slug is the most common. However, all types of slugs and snails can destroy garden plants, the problem being particularly difficult in May and June when plants have soft, tender growth although it can persist throughout the summer, especially if it’s been a wet one.

Understanding the lifecycle and habits of slugs is helpful in developing management strategies. Slugs require moisture in soil and vegetation, though in dry spells they can move down into soil to find damp areas, often following existing wormholes or other openings. Adults can live through winter in these areas (not in Florida! Apologies, Ruth…), seeking shelter from the cold under ground, under garden mulches, and under other garden litter, including composted yard waste piles. Many bothersome spring slugs, however, hatch from last year’s eggs laid in pearly clumps of 40 to about 100. These little spring slugs, often smaller than a pencil eraser, eat voraciously and become about an inch long a month after emerging. Slugs can eat 30 to 40 times their weight every day!! In a year, these little devils will be full size - if they are fortunate enough to escape the control tactics of the motivated gardener.

In the garden season, both slugs and snails enjoy lush weedy areas around gardens to hide in, and soils rich in calcium and organic material (such as amended garden soil). An irrigated, mulched garden with carefully prepared soil presents slugs with the ideal habitat. The fact is that slugs like precisely the same garden conditions suitable for young vegetable seedlings and many herbaceous perennials. But, don’t give up your good garden practices - go sleuthing for slugs instead!

Look for slugs under leaf litter and mulches, under pot rims, and under containers of young plants. Many summer annuals can suffer from slugs climbing up pots and containers, reducing marigolds and petunias to fibrous tatters before you even get them into the ground. Slugs are feasting at night, so keep your containers of plants inside on a cool pantry counter until you’re able to plant them.

Some obvious traditional control methods work to reduce populations. In spring, look for and destroy the pearly egg masses laid under rocks, in soil, or in garden litter (this speaks well for good fall garden clean-up). To determine your potential pest population, make traps such as dampened paper towel cardboard tubes, damp, inverted clay flower pots or saucers with one edge slightly raised by a stone or pot shard. Check under some favored slug areas like emerging hosta leaves and perennial ground covers. Slugs migrate from these areas at night to dine on your garden plants.

Handpicking does help, particularly if done in early evening at dusk as they come out to feed. Of course, all slugs will feed during dark, moist days (like many we had this summer). Put the captured slugs into containers with secure lids such as a glass mayonnaise jar containing soapy water. Live slugs can push of pop-off lids and can eat their way out of cardboard containers.

Other than hand-picking , consider some barriers as garden management techniques. Various sources in home gardening magazines have recommended putting sand, diatomaceous earth (made from shells of tiny sea creatures called diatoms), wood ashes or lime (neither a good idea as both can change the pH of your garden soil), and eggshells. Most of these barriers work only intermittently and not at all when wet.

Many gardeners rely on beer traps, filling an empty tuna fish can and pushing it into the soil leaving the rim extending 3/4 inch above the soil. (If the rim is flush with the soil, beneficial insects like predatory ground beetles may fall in.) I used to think that it was the yeast in beer that attracted the little buggers until recently. And I quote from Amy Ivy - “In Marvin’s famous beer trap study, he found that the yeast in water was not very attractive at all, not even non-alcoholic beer. His slugs preferred the real thing to anything else.” (Marvin Pritts is the head of the Department of Horticulture at Cornell.) This is a good example of what sounds like a home remedy but has actually been researched at a major university.

There are poison slug baits on the market, but they must be used with care as they become “attractive nuisances” for pets and small children left unattended. Also, slugs can sometimes crawl off and slime away the poison (nerve toxin), recovering from it on a cool, moist day, so reliance on bait alone won’t manage a garden problem. If you do choose to use bait, read the label carefully and take all the recommended precautions.

As with most of our challenges in the garden, there’s no silver bullet. And, there’s no substitute for the astute gardener scouting, identifying the pest correctly, using a combination of practices to minimize the damage, and having some tolerance. If Mother Nature can live with some imperfections, perhaps you can, too!