This is one of 10 stories on "Green Gardening Choices for the '90s: Alternatives to Lawn and Garden Chemicals" to be published before this year's Green Garden tour.
Judging from the tattered iris leaves and empty spots where the lettuce and marigold transplants were, mollusks are on the move in our gardens. The gray garden slug sliding about on its single foot, and its ally, the brown garden snail, are among the most damaging and persistent of Northwest pests.
The snails may surprise you. They are now common in many gardens here. Both mollusks feed on tender vegetation of all kinds, and are most active at night or on cloudy, cool days. On hot sunny days they hide - under groundcover, a flower pot, or your deck.
Slug and snail control takes vigilance. Go out after dark and hand pick them, or look for them early in the morning while they are still on your plants. Disposal methods depend on the gardeners' sensibilities; it's easy to drop them into water containing a little alcohol, or toss the container in the freezer for nearly instant slug demise. Some people carry weeding tools to dispatch the critters.
If you are growing iris, you are probably especially frustrated. German iris could be called a "trap crop" for slugs and snails. They scoop out chunks of stems and hollow out buds, wrecking the whole year's blossom. Patrol often and look under deck pots regularly. And yes, they still like beer; put out in shallow containers.
Copper barriers work, too
Copper barriers, used for nearly 10 years in California to protect citrus trees from snails, offer another nontoxic form of protection, and one that is new in the Northwest. Orange growers developed the method of fastening copper around the tree trunks. If you have a raised-bed vegetable garden, installing copper barriers can help repel the slugs. The copper strip must be at least 3 inches wide with a top edge that folds over to form a little ridge.
The copper strip lasts for years. You'll notice weathering, to a greenish-blue which does not harm the effectiveness against slugs and snails. If you want the copper to look pre-weathered in your garden, you can brush it with a solution of warm saltwater. The copper strip works on the same principle as a copper boat bottom against barnacles; the mollusk starts across and is greeted by an electrolytic reaction, thus retreats in discomfort.
University studies in California and Colorado have shown copper barriers to be quite effective if properly installed. Escargot producers in California use the copper barriers inside growing areas and bins to keep their crop from wandering out.
A representative for the Snail Barr company noted that the barrier's effectiveness is reduced if it's driven directly into the ground. Garden soil washed against the copper by rain or irrigation can leave splotches that the slug may be able to cross. If you have open garden vegetable beds, you could staple the copper to bender board and place that combination around the area. Wear heavy gloves to handle the copper. It's sharp. And if the barrier is ripped or torn, you'll have to restaple. (Don't go hitting it with your weed-whacker.)
Keep' em outside
Remembering the principle established by the escargot growers, check to be sure you don't have slugs trapped inside the barrier. A slug will pull itself up on a nice lettuce leaf, skipping the copper, and spend the rest of the summer inside your salad greens. Copper barriers would be easiest to use with raised beds and are certainly worth trying for chemical-free control. You can use Snail Barr, Dr. Harvey's Copper Mountain (copper-impregnated plastic available at local nurseries), or generic sheet copper. The commercial barriers are still rather difficult to find in the Northwest. In Washington, you can call Snail Barr at (619) 749-7132.
For more information call Dial-Extension, 296-3425 for Tape No. 123, "Slugs." To receive brochures on alternative pest controls (available in late May), or a map to the July 9-10 Green Garden Program tour, call 547-7561. To schedule a slide presentation on alternatives to lawn and gardening chemicals, call 632-1545.
The Green Gardening Program is a collaborative effort of WSU/King County Cooperative Extension, Seattle Tilth, and the Washington Toxics Coalition. It's sponsored by the Seattle Solid Waste Utility and funded by the Local Hazardous Waste Management plan.
Gardening is published Friday in Scene and Sunday in Home/Real Estate.