Hill Gardens of Maine - Dealing With Slugs & Snails

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Slugs & Snails
by Fred Davis, MG, Hill Gardens of Maine (To view other articles, click: Archives)

Additional comments about how much lime to use to discourage slugs added 9/7/2002
Using household ammonia as a "slug-a-cide"
Using copper foil or screen as a "barrier"

Welcome through Fred's Garden Gate! After a few days of warmth and occasional showers, it seems that certain types of insects and plant diseases proliferate. Clouds of mosquitoes almost always follow close on the heels of showery summer days. Molds, fungus and mildews are other trials that must be faced by many gardeners around the globe.

But the peskiest of all are the hoards of slugs and snails which appear seemingly from nowhere, competing with each other to see which can eat the most. A few of the slimy critters here and there are not all that much of a problem, but if your garden is near the woods (or in the woods like ours) watch out! To compound the problem, if one of these garden-malefactors meets another (a very frequent occurrence!), you'll have 50 or 60 eggs to contend with. Multiply that by the number of slugs or snails you see, and it almost boggles the mind.

Slugs and snails are essentially the same type of creature, mollusks, the difference being that one has a shell (its house) and the other doesn't. Controls and deterrents are much the same for both but, because slugs seem to present more of a problem to large numbers of gardeners, the remainder of this discussion will focus on those without a shell.

Here in Maine, long-time gardeners refer to the most destructive variety as "banana slugs." Large, yellow/orange creatures ranging between 1/2" to 1-1/2" long, they rampage through many New England gardens leaving an alarming trail of destruction and slime. Other, usually smaller, types frequently march side-by-side with their larger cousins devouring practically anything in their path: any dead or living plant, flower or fruit, especially tiny seedlings.

Most hosta aficionados will tell you their worst enemy is slugs! In fact, some varieties of hosta seem to be slug-magnets! Yet a few hosta growers – myself included – seem to be very nearly free of the pests. Read on to learn the secrets! (By the way, slugs also have a particular liking for yeast. Remember that last point, it's something we can use to our advantage a little later on.)

First, and probably most important, never - ever - let a slug get away! You must be ruthless in your search for and destruction of these fat, slimy and hungry creatures. I prefer not to use poisonous pellets, liquid or granules to reduce slug and snail populations. Most are exceedingly toxic to pets, children and wildlife, including birds and small animals. If you feel you absolutely must use them, put a few under a board or some newspaper where slugs crawl to hide. Always wash your hands thoroughly after handling slug baits. Make certain that none of this deadly material escapes into Nature or finds its way into water supplies. Better yet, show your disdain for widespread application of hazardous environmental poisons by not purchasing them.

A much safer, yet more labor-intensive, method is hand-picking. Walk through your garden either early in the morning or evening with a mason jar half full of very salty water, and a spoon. Scoop 'em up and let 'em take a swim. They can't! Look under boards, stones, thick weeds, pieces of rotting bark, anyplace where it's cool and damp.

Saucers of beer? Forget it! You may nail a few—but there’s a better way. Snipping the creatures in two with sharp scissors? Too labor-intensive—and yucky! Sprinkled table salt? Yes, salt does cause them to dehydrate and die, but that’s not the answer either. Which brings us to two highly-effective methods: one to thin the crowd, and another to prevent their re-entry into our gardens.

Large populations can be quickly (that’s a relative term, depending on the numbers in your garden) reduced through the use of yeast-baited traps. Slugs love yeast! That’s why they’re minimally attracted to saucers of beer. A more concentrated – and therefore more attractive to slugs – form will quickly draw them to their demise from several yards away. Here’s the deal: collect two one-quart Mason jars with lids and pour two cups of warm water into one. Add a packet of dry yeast, and one teaspoonful each of salt and sugar. Mix thoroughly and divide the odiferous concoction between the two jars. Nuzzle each jar into soft garden soil at an angle so the lower lip of its opening is just at ground level. Slugs smell the yeast, travel to its source, crawl in and drown. Every two or three days, collect the slimy mess and either flush it or put a tight lid on the jar and place it in the garbage. Place yeast-trap jars every six to eight feet where populations are high.

Now it’s time to get to the real nitty-gritty! There are a few simple, inexpensive steps which you can take to finally keep slugs out of your garden once their numbers have been reduced to manageable levels. But first, a question.

Where do you suppose you’ll find the most slugs in Nature? Answer: back in the dark, damp, cool woods—where, likely as not, pH conditions are highly acidic. Their physiology is acidic. Alkaline conditions are anathema to slugs and snails. Given the choice, they will avoid a pH of 7.0 or higher like the plague. OK—so most of the common, you’ll-find-them-in-every-garden annuals, vegetables and perennials we like to grow prefer a soil foundation pH of somewhere near 6.5 to 7.5. Hosta, for instance, like it sweet (alkaline). Delphiniums – another slug favorite – like it sweet (alkaline). Iris (definitely a choice slug-snack) like it sweet (alkaline). Get the picture?

I’m fond of challenging visitors to our 2-1/2 acre gardens to find 25 slugs. They can’t. Although surrounded by woods and "swamps" seething with slugs, these slimy malefactors will not venture into our gardens. That’s because our garden soil is constantly maintained at the pH level which most plants actually prefer in order to be vibrantly healthy, and look and perform their best. So, the short answer is: test your soil’s foundational pH, adjust it to optimum with lime or wood ashes, then, when all’s done, apply a light, dusted coating of lime or ash to the entire garden surface including paths, composting area, lawns and surrounding margins. In our gardens, at least, it works!

There is one highly effective barrier that stops slugs in their tracks. Slugs have a definite dislike of copper. It doesn't kill them, but sets up an invisible "roadblock" of sorts. An electrolytic effect results from contact between copper and their slime—giving them a tiny electric shock. Quite a deterrent. There are no electric wires to mess with, and the foil is readily available in some garden center and retail hardware outlets. Easiest would be to use the Internet: Organic product supplier, Peaceful Valley Farm & Garden Supply, Grass Valley, California 3" by 20' roll; 3" by 100' roll.

You could also use copper window screen. Most hardware stores still carry it.... and it's a good deal less expensive than the foil. Cut it into about 5" wide strips and bury about 2" of that so that at least 3" sticks up above ground like a little fence. It could also be laid flat on the ground all the way around the bed or cold-frame to be protected. Just like a little minefield.

On a recent trip out to the central valley of California (Salinas, if memory serves), we stopped at a garden center and found a similar product. A thin—almost painted on—layer of copper bonded to a stiff, probably waterproof, backing of a cardboard-like material. It, too, was less costly than the rolls of all-copper.

There is an inherent and hidden danger to using copper foil or screen. As an "easy fix" you're liable to use it as a crutch to avoid dealing with the real issues of garden neatness and cleanliness, and maintaining surface soil pH.

The best method of slug and snail control isn't control at all...it's prevention. Three little words: Keep it clean! Eliminate trash, piles of weeds and rotting plants or anything else they can hide in or under. A clean, neat and well cultivated garden is apt to have far fewer slugs. Combined with correct pH, the phrase won’t be "Where’s the beef?" It’ll be "Where’s the slugs?!"

Consumed by Slugs!

More and more frantic questions are arriving about garden-invading slugs and snails. The most recent came in the form of an email (I love email!) from Kate, after reading the above article, Slugs & Snails, in which I recommend surface application of lime to discourage slug travel. I had neglected to be very specific about how much lime to spread over a given amount of space.

Here’s her question: “My garden is being consumed by slugs—they have devoured the campanula and are now working their way thru the hosta. Please explain what to do with the lime. I am beginning to feel a little bit like Bill Murray. —Kate”

It occurred to me that this simple, inexpensive—and effective—method of dealing with a very common pest should be shared with gardeners everywhere. Here’s my response:

            “Greetings, Kate! Yep....been there...done that! Until, that is, I discovered that slugs simply cannot stand alkalinity brought about by the light surface distribution of ground limestone or screened wood ashes. That should do the trick for you…but, first:
            It'll be necessary to reduce slug and snail population levels. Here's how to do that: Forget the saucers of beer which are only marginally effective (meaning that the process will take probably ten times as long to reduce populations by less than half the original levels. Who needs that?!). Slug-snail baits are also out of the question due to their potential negative impact on the environment, and the danger of toxicity to birds, household pets, and always-curious children.
            Household ammonia at the correct dilution not only destroys slugs, at that dilution the solution actually provides a source of nitrogen which plants absorb through their foliage—"foliar feeding". Mix 1 part household ammonia (I prefer the non-sudsing type, but either works well) with 5 parts of non-chlorinated, non-softened water—for a total of 6 parts. A few others have suggested a much stronger dilution...and, yes, it'll kill slugs quicker but there's a higher risk of burning relatively tender new leaves. The 1:5 is highly effective—with far less risk of scorched foliage.

            You'll need to use some sort of a sprayer—either a garden type or an old Windex type bottle.
            Slugs are highly active at dawn and dusk, when conditions are damp, cool, and calm. Walk around your garden during those times for two or three mornings and evenings, spraying everything in sight. Be sure to check anything that they might hide under: boards, newspaper or plastic mulches, cardboard, boxes, containers.
            Now—after the population has been decimated by your persistent ammonia attacks—is the time to adjust the surface pH with lime or ash. Very early on a following cool, damp, calm morning, distribute the material evenly over the entire garden—paths, beds, lawns...everything. I do that by carrying a small pail of lime under one arm, and an old cat food can in the opposite hand; I wear an inexpensive painter's mask (a medical/surgical mask works too, but doesn't fit quite as tightly), and walk backwards through the gardens, vigorously slinging lime into the air at about head-height. When done, the whole place looks like a dense fog....gradually settling over everything.
            Later that same day you can go back with a hose and hose-end nozzle to rinse foliage so the garden looks better...but remember: a coating of lime or ash must remain on the soil surface where slugs and snails prefer to crawl. If you cultivate or disturb the soil later, you'll need to reapply a dusting of lime.
            Another factor is slug eggs that are already deposited in the soil. They're going to hatch later on, so you may eventually need to repeat an ammonia spray treatment. Also consider that hosta like their foundational soil pH considerably sweeter (higher pH: neutral to slightly alkaline) so don't forget to add your lime this fall—four or five pounds in a spot 10' x 10 'x 10' (100 square feet)—cultivated about three to four inches into the soil. Actually, just maintaining correct soil pH in your hosta beds will discourage the travel of most slugs.
            That should solve the problem for you. Good luck...and drop by my email box any time. (By the way...your complimentary copy of the book "Keys To The Garden Gate"is waiting for you.)

Until next time, do what you must to stay ahead of the fast-growing, cool-weather weeds that will be doing what they must to take over your garden this fall.

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