Controlling Snails and Slugs
Q. Carol in Chesapeake, Virginia (who listens to us on WHRV) writes: "I have been buying flowers and setting them outside in their original pots every spring, summer and fall for the past 25 years--including geraniums, verbena, pansies, and zinnias.
"The past two years I've had a terrible problem with snails eating the plants. I have tried nearly every remedy I could find on the Internet with no success, including beer, coffee grounds, Epsom salts, Sluggo, Vaseline around the tops of the pots, mothballs, garlic spray, eggshells, and the balls from sweetgum trees. We never saw snails previously and have not done anything significantly different in the areas around the pots."
A. Before we address your molluskian marauders, we have to review your Internet list as a cautionary warning to others. There is no reason to expect coffee grounds, Epsom salts or garlic spray to be effective against these pests, but at least they're safe. Mothballs are NOT safe, and it's shocking that they're still for sale! These little balls of kidney cancer in a box are extremely dangerous to you, pets, wildlife and just about every living thing on the planet. Whatever site recommended them should be ashamed of itself.
Now let's look at your could-have-worked choices--both for slugs and snails.
• Beer: Beer can be highly effective, especially as a diagnostic tool when gardeners aren't sure what's causing overnight damage to their plants. (Both snails and slugs work at night and thus often go undetected.) To use beer effectively, bury some small containers near the affected plants--things like cat food cans and half-pint containers from the deli--flush with the soil; you want to make it easy for the pests to fall in. Then, as evening falls, crack a fresh can of beer and fill the containers. Do NOT fill them during the day; they'll be useless by the evening. Do NOT use "stale beer"; slugs and snails like stale beer about as much as you or I would. If this tactic proves to be effective, buy a case of the cheapest beer you can find, empty the containers of their dead, drunken quarry every morning and refill your traps every evening.
• Products like Sluggo and Escar-Go! are pelletized yeast laced with iron phosphate. The slugs go for the yeast and then are incapacitated by the iron. A light sprinkling on the surface of the soil around your plants should be effective; don't pile it up. Mist it slightly at dusk for optimum results.
• Vaseline is interesting. I suspect the mollusks might actually find it comforting, as it's a lot like their slime. But I can't see it hurting them.
• That brings us to eggshells and "itchy balls" (that's what we used to call those round spiked sweetgum tree seed heads when we threw them at each other as kids).
• Eggshells: There is some thought that slugs won't cross over a line of calcium--but for that to work, you'd have to crush the shells up very fine. A commercial product known as diatomaceous earth (or just DE) would be a better choice; to us it looks and feels like flour but is very sharp on a microscopic level. It needs to be bone dry to be effective.
• And if you surround the plants with enough itchy balls, I can't imagine snails trying to mollusk their way in.
Now--you say that you put out your plants in their original store-bought containers every year. I suspect that because of the relatively small size of such containers you're probably overwatering them--and/or watering them at night, just before the snails go to work. Only water your plants in the morning; and don't water them every day.
You could also try capturing the pests under boards. Snails are a huge problem in many parts of California, and The University of California Department of Agricultural and Natural Resources suggests laying down wooden boards that have little stones or something holding them up about an inch off the ground. Slugs and snails will retreat to this easy protection at sunrise. Later in the day, go out and scrape your catch into a bucket with some soapy water in the bottom. Taunt them as they drown.
Copper can be wildly effective. Slugs and snails essentially get electrocuted when they touch copper, which is very cool to watch. You can buy thin strips of copper flashing at hardware and home improvement stores and wrap it around the outside lip of the containers. Wear good gloves if you pursue this option; copper flashing is sharp. Martha Stewart once solved a similar problem by hot-gluing copper pennies around the tops of her containers, which might be more workable if you transplanted your posies into bigger pots to get a wider surface to work with.
Another option is to place piles of lettuce leaves and citrus rinds on the ground around the pots in the evening and then go out late at night or early in the morning and collect it as the beasts are feeding. Similarly, you can wet the plants down like blazes in the early evening and then go out at midnight and handpick the pests. But this is the only time you should water at night.
And be sure and check the undersides of your containers for snails-in-hiding and/or their eggs; these pests love the moist dark areas under pots. And finally, don't pour salt on your snails when you do catch them. Yes, it makes them writhe and dissolve, but it's also bad for your plants.
Ok--move one to the sidewalk and salt it. Taunt the ones in hiding as you do.