This article is written in two parts. The first part is what I call my Slug Manifesto. If you’re short on time and just need to know what works without needing to know the details of why most of what you read on the internet is false, scroll down to the bottom of the post until you get to the “what works” section.
I live in the Pacific Northwest, on heavily shaded and moist acreage which is prime slug habitat. The slugs out here grow to enormous sizes–five inches or so. I’ve dealt with slugs before when I lived nearby in the city, on a 5,000 square foot postage stamp lot and so I knew that dealing with the problems that they cause could be exceedingly frustrating. But nothing prepared me for the reality of what what was in store for me in attempting to grow food out here in the country. Not only were my plants damaged, but many times the entire planting would be completely wiped out overnight. Everything I tried to do to get rid of them failed.
But I was determined to figure it out. One fall, a couple of years ago, I decided to declare WAR. I would find out exactly what worked and what does not. I did slug experiments in a styrafoam box that we no longer had use for and recorded the experiments with photographs. What I found out was shocking! The absolute truth of the matter is that none of the purported methods that you read about work. Nearly every "cultural" method is a waste of time, money and resources. All of this information that I learned by trial and error was further verified when I took the Master Gardener Course through Oregon State University. Would've been nice to know that before I went to all that work. Oh well! What I did was this: I got a white styrafoam box and about 30 slugs (took me about 5 minutes to find that many). I tested each one of the popular internet methods. Here are my results:
Copper: supposedly, copper is supposed to "shock" slugs, and if you place copper in the garden it will repel slugs. In this photograph, I placed some copper "slug" tape on some cardboard and placed a lettuce leaf on it. It didn't take long (like a half hour) before the slug crawled right up onto the copper and started munching away.
In addition, I tested the "copper mesh" strategy. The theory is that if you twist copper mesh around the stem of the plant, it will repel slugs. Unfortunately, as you can see in the photograph, the theory did not hold up to reality. When I published the findings on my website, the seller of the product criticized me for not putting the mesh tighter around the stem of the plant. My rebuttal is this: First, the edges are extremely sharp and having something this tight and sharp around the stem is likely to injure the plant. Second, it is entirely impractical to go out into my garden, where I could likely have a thousand plants, and maintain these little gadgets. My conclusion: copper is a wildly expensive dud.
Wood ash: The salinity or alkalinity of wood ashes is supposed to repel and or kill slugs. But tell that to the slug in my picture. I had placed slugs on one side, lettuce on the other. The slug quickly crossed the slug line and devoured the lettuce leaf. Another dud. Besides that, the salinity of wood ashes is supposedly damaging to your garden.
Eggshells: many gardening writers state that eggshells placed around plants will deter slugs. Well, tell that to the slugs in my photographs, who are happy munching away on lettuce leaves amidst copious amounts of eggshells. The way that eggshells are supposed to work is this: slugs have a delicate body (nonsense--have you ever tried to crush one with your bare hand?) and, when the slugs run into them, turn the other way and are thus repelled. Well, maybe slugs are that smart, but I sincerely doubt it and it doesn't keep the slugs from multiplying out of control in your garden. By all means, adding eggshell to your garden isn't going to hurt and your garden is going to need the calcium anyway, but it is not a reliable way to get rid of slugs. The same principle applies to all "course" objects that are recommended, such as oyster shell or hazelnut shells. To illustrate my point, check out this video of a slug happily crawling across a knife blade.
Diatomaceous Earth: this is a substance that is commonly used as a pesticide for slugs. I came across some of this stuff, which we will call DE for short. When I test it out, it simply didn't work. Didn't deter the slugs, nor did it kill them. I actually rolled the slug around in the DE, and the slugs were fine. Note that this substance must be dry in order to be an effective pest control option. Slugs come out when it is wet, not dry. Furthermore, DE is a very dangerous lung irritant (asbestos anyone? yeah I didn't think so!).
Coffee grounds: I'm not sure why this theory came about, but something about the caffeine content or perhaps the abrasiveness of coffee grounds is supposed to repel slugs. Wouldn't this be nice? After all, coffee grounds are given away freely to us who will compost them for our gardens. Unfortunately, this method was yet another dud. It just didn't work.
Traps: oh I had high hopes for this one. The thinking behind the trapping method is to use the slug's natural behavior as a trapping mechanism. Slugs will hide under nearly anything, but they particularly like wood. I set out a few wood boards but didn't put a dent in their population. So I thought well, maybe I should use as many possible traps as I can, trap them all, and finally be done with the problem. I grabbed about thirty boards, placed them all under my plants, and, each day went out and destroyed the slugs. It too about a half hour each day to flip over the boards and look closely to destroy the. At the end of two weeks, I was still finding just as many slugs as on day 1. It was an exhaustive process, I wasn't getting anywhere, and so I chose to abandon the idea. Please note that had I left those traps in place, or only check the traps every few days, the boards would have actually exacerbated my problem by providing them with habitat.
Beer: I'm going to walk out on a land mine here, as this is the most beloved method of all. The process is simple: pour beer into a shallow container and the slugs will happily crawl in and drown. On the surface, this method seems to work, but the reality is entirely different. Yes, some slugs do crawl in and drown. But most don't. I tested this by using my little box and several containers filled with beer. I put about 30 slugs in the box and observed them over about a week. Only about three drowned, but the beer was slowly going away. Slugs were drinking it alright, but they weren't drowning. In essence, I was just feeding them. Beer is an expensive (non)solution too. Last time I priced it,the least expensive price was .71/pint. Considering that the traps must be refilled regularly, the price for maintaining these traps is absurd. You're certainly not getting the most bang for your buck. Save your beer for you, not the slugs! By the way, have you ever dumped out dead slugs floating around in stale beer? GAG. In conclusion, when I read articles by supposed "experts" in this field and they continue to purport that some silly substance like coffee grounds will solve your slug problems without testing the method, I want to should from the rooftops: "Hey! We're actually trying to grow food over here! Your articles are only adding to home-gardener's frustrations and we're more likely to give up our gardening efforts so just stop it!"
Now for the "what works" section:
Reduce Habitat. Slugs love hiding under mulches. They particularly like hiding under old boards or wood of any kind. Keep the ground bare as much as possible. Cover crops are wonderful but also provide hiding and breeding ground, so plan accordingly. Invest in a high quality, sharp hoe.
Over-seed and progressively thin your plants. This technique overcomes many gardening problems.If you live in a heavily infested area such as mine, you will just have to change your gardening mindset and learn to expect slug damage. By planting twice as many plants or seeds as you need, you will at least partially outwit the slugs. When you plant lettuce, plant LOTS of lettuce seed. This way, you can progressively thin out your plants and eat your harvest earlier! Of course, this will mean that you will need to thin the plants that you don't need, because you don't want to crowd them, which will reduce their water and nutrient availability. Tip: when you purchase seeds through a reputable seed company, you typically have the option of purchasing significantly larger seed packages, which drops the price-per-seed down significantly.
Physically destroy the slugs and their eggs. The quickest, most efficient way to do this is by going out at night with a headlamp and scissoring away. Yes, you could drop them into water, this takes extra effort and the slugs can just crawl right back out. Besides, slugs are high in protein and all that "green" that they eat is high in nitrogen. Better to reuse their resources and recycle the nutrients back into the garden. Many folks swear by using a salt shaker in lieu of destroying them. But this means wasting money on salt, adding more salinity to your garden, and makes your food icky when the slugs disintegrate all over the leaves. Trust me, its gross. For folks such as me, who have large gardens, this process can be quite laborious and it is probably more efficient to just use bait.
Keep your plants as high off the ground as possible. If you let your tomatoes sprawl all over the ground like I did in that one disastrous year, you are asking your slugs to come and eat your tomatoes!
Attract natural predators to your garden. Provide habitat for small reptiles such as snakes, frogs, salamanders. If you have chickens, they will only eat the smallest slugs, no larger than the size of your pinky fingernail. Unfortunately chickens do like to eat your plants as well, so you'll have to allow theme to forage in the area when you aren't actively growing. Carol Deppe, author of The Resilient Gardener, says that she likes ducks for per slug patrol. She fences off an area near her garden for her ducks and says that the duck poo attracts the slugs away from the garden and the ducks gobble them up happily. Also, I've read that some wild birds are natural predators (such as robins) but I have yet to test this theory. I figure birds are a great addition to all gardens except those where you are trying to grow fruit anyway.
Plant slug-resistant greens. I was delighted to find out one year that Miner's lettuce and corn salad seem to deter slugs! Yahoo! The good news is that miner's lettuce self-seeds readily (and survives well in part-shade!), and you can create a perpetual salad garden.
When all else fails, use bait. There's a few different chemicals that you can use. The classic chemical, metylaldehyde, is an environmental nightmare and a no-brainer----DON'T use it if you care about your kids, dogs, wildlife, etc. Check out this post to find out more. The other chemical, the "organic" option is called Iron Phosphate. It is commonly called: Sluggo or Escargo and there are a few other names. Slugs eat it, dehydrate, and die. The substance itself breaks down into fertilizer. The bummer about iron-phosphate is that the price is astronomical: as much as $11/pound. I did a little price shopping last year and found that the cheapest way to obtain this stuff is to purchase extremely large, 50 pound bags. The price can go down considerably: as low as $2.80/pound.
So there you have it. My slug manifesto. Have you ever had slug issues? How did you handle (or not) the problem?