Features and Occasionals

In the Garden: Snails and Slugs

By Margaret Park

Certain armies do march on their stomachs. I’m referring here to those life forms known as gastropods whose name means—literally – stomach foot. Better known as snails and slugs they actually are much more into making love than war—they’re hermaphroditic, so every one of them is a potential mom. Yet, when I see a dozen or so snails gathered around the stubs of petunia plants, the term “army” doesn’t seem off base.

Snails and slugs strike by night when the ground is moister, temperatures are cooler and we’re not around to spot them and do something about them. Picking them up and moving them away is an effective deterrent. Placed on lawn areas or in the clover patch, they’ll get into less trouble for a while.

Snails are rather peaceful creatures and do have decorative appeal. They surely have roles to play in the grand scheme of things. We can limit their destructive power rather than killing them simply because they eat our plants. Larger plants can handle some nibbling, so even if the gastropods do manage to find the flourishing lettuce patch, they are little creatures and don’t eat that much.

However, they cause unrecoverable damage when the garden is freshly stocked with tender seed­lings. The summertime sowing of the fall crop can be a particularly hazardous time for the vegetable garden. Snails and slugs can eat every seedling down to the ground.

Tips for enticing them into collection spots have been around for ages: Upside down flowerpots, and bits of wooden boards strewn on the ground will become snail and slug gathering places where they can be found in daytime and carted off. They supposedly will not traverse copper, since copper reacts chemically with the soft tissues of their underbellies. However, after watching snails casually crawl over strips of copper flashing, my confidence in this advice dropped sharply. Surrounding vulnerable plants with eggshells is another often mentioned folk remedy. While I haven’t tested eggshells as a deterrent, I have tried other kinds of sharp or pointy materials without much success. There are no less than a dozen YouTube videos showing snails crawling over razor blades.

In recent years, scientists at the Agricultural Research Service in Hawaii looking for ways to control an invasive frog species chanced upon a non-toxic repellent for snails and slugs: caffeine, a suspected neuro-toxin to these mollusks but obviously not harmful to humans and pets. Researchers are still investigating agricultural applications for using caffeine as a deterrent.

Many home gardeners do report success spraying leftover coffee on plants. Encircling vulnerable plants with coffee grounds is another popular strategy, especially for gardens with generally alkaline soils, as we have in the Salt Lake area. Since the coffee grounds are acidic, they should even help balance soil pH.

Armed with all of this information, I set out to test the most effective methods of non-lethal snail control that I could use in my home garden. (There isn’t much of a slug population in my area, so my discoveries may only hold for snails and perhaps not for slugs, though I think they’re worth a try.) Following are some of the things I’ve learned.

Copper: The copper strips that my husband nailed to the wooden border around the vegetable garden may have worked initially when the surface was clean and untarnished, but keeping the copper surface fresh demanded more maintenance than I was up for.

Caffeine: The grounds have a tendency to disperse with watering and also lose their potency after a few days. Corralling the coffee grounds with inch-high rings cut from plastic milk or soda bottles helped the coffee stay in place. Concentric rings with coffee in between the larger diameter outer ring and smaller inner ring worked even better, but the grounds still needed to be refreshed every day or so.

Tea leaves: Tea leaves had little deterrent power compared to spent coffee grounds.

Onion oil: Onion pieces and leaves can be steeped in foliar spray solutions such as compost tea, or Activated EM solution to make a pungent spray mix that the snails avoid, and the solution itself is nourishing for the plants. I tested a compost tea onion spray on bean and cucumber seedlings with very good results. Daily spraying is advisable.

Wire cage barrier: I came up with this strategy after losing most of my fall crop seedlings last summer. For spring planting, I shaped quarter- inch hardware cloth—a kind of wire mesh—into a box-like cage (without a bottom) and placed it over newly seeded areas, making sure it was firmly set into the soil. The five-inch-high sides of the cage gave the seedlings plenty of headroom to grow to a size less susceptible to overnight destruction. These cages kept the snails at bay for many months without having to do another thing for protection. The biggest drawback to the wire cage is the initial expense. However, given the longevity of metal and my practice of successive crop sowing, the investment in hardware cloth will eventually be a cost effective solution compared to buying new seeds or plants lost to snail consumption.

Watch Margaret Park make the wire cages on Facebook at Center Square Gardens: http://www.youtube.com/watch?v=-1CJIp2pj2w

This article was originally published on June 28, 2013.