How to Keep Slugs Off Cabbage and Other Cole Crops

With the possibility of having up to 200 slugs on every square yard of your garden in cool humid climates, your cabbage plants and other brassicas may be in peril.

Such a robust population can strip your garden of cole crops and other veggies.

Close up of a slug crawling on a damaged cabbage leaf.

And each of these terrestrial gastropod mollusks can produce 400 eggs a year; and they are hermaphrodites meaning they all have both male and female sexual organs and can lay eggs.

However, you can fight back and prevent the slimy fiends from damaging your precious plants.

We at Gardener’s Path will describe methods you can take to keep slugs from devouring your cole crops.

When You Have Slugs in Your Garden

The shiny trail of mucus is a giveaway that you have slugs or snails in your garden.

They hide out during the day by burrowing into crevices in the soil and hide under rocks, boards, or dense vegetation.

Night is when they do their damage.

What’s at Risk?

Slugs love to eat all cruciferous vegetables including (but not limited to):

  • Bok Choy
  • Broccoli
  • Brussels sprouts
  • Cabbage
  • Collard
  • Cauliflower
  • Kale
  • Kohlrabi
  • Mustard and other crucifers
  • Radish
  • Rutabaga
  • Turnip

Tell-tell signs includes large holes being chewed into the leaves.

A dozen slugs on cabbage plant with extreme damage to the leaves.

A serious infestation can make a plant look like lace, seriously damaging the crucifer’s ability to perform photosynthesis.

How to Manage an Infestation

Trapping

Classic methods such as putting cups of beer or milk in your garden are surprisingly effective. The best technique is to make a little hollow in the soil big enough for the container to fit in so the lip is at ground level when the vessel is inserted in it.

A large number of brown slugs caught in rectangular beer trap set in blue rectangular tub inset into the earth.

Fill with beer or milk and let it sit overnight. The creepy crawlies will be attracted to it, crawl in, and drown. Empty and replace in the morning.

However, you should be prepared to set out a lot of traps – one every square yard.

A board is another option. Simply place a board over rich organic with lots of compost. Slugs will craw under the board to escape the heat during the day. Towards after merely lift board, scoop them up. and either relocate or eradicate (with salt).

A board laid near a veggie garden as a slug trap. Close up view with a burred background.

To make it even more effective, you also bait your board traps with vegetation (cut potatoes, grapefruit skins, or even cabbage leaves!).

It is important that you check these traps daily.

Erect a Barrier

Slugs can be surprisingly mobile, moving as much as a mile over a few days. Therefore, you want to ban them from your garden.

Macro shot of a slug with crushed eggshell stuck to its body.
Having crushed eggshell stuck to your body is no way to go through life, son.

A barrier can be a good way to do this. You can make a two-foot wide path of crushed oyster shells, crushed eggshells, cinders, wood ashes, sawdust, or sharp sand.

Harris Food Grade Diatomaceous Earth via Amazon

Diatomaceous earth is a particularly fearsome substance to terrestrial mollusks because it is lethal to their soft bodies.

Other alternatives include wire screen or copper strips.

It’s not fully understood why slugs don’t like to cross copper, but it may be that low levels of electricity can naturally pass through the strips.

26 Gauge Copper Flashing 2″x120″ via Amazon

One bit of advice, many of the copper strips sold in garden shops and the big box stores aren’t wide enough to be effective. The strips need to be at least 2 inches wide to prevent these veggie-eating gastropods from arching themselves over the barrier.

Use Black Plastic Mulch

When you use black plastic mulch, the soil will heat up and dry out. Therefore, this will discourage slugs from hiding in it.

Avoid Organic Mulch

Slugs like to hide in organic mulch, so your best bet is to avoid it if you have an infestation. If you do insist on using mulch, at least thin it out, so the soil will get warm and dry (and be less inviting).

Remember these slimy mollusks can overwinter in organic mulch.

Plant in Raised Beds

Since raised beds of cabbage and other cole crops are more likely to dry out, they will reduce the likelihood of infestations in your cabbage plants.

Let Ducks Loose in Your Garden

Unlike chickens, which eat slugs and other pests, but damage your garden in the process, ducks are efficient predators of water and land mollusks and are much less likely to harm your cruciferous veggies.

A group of four brown Indian runner ducks in a backyard garden patrolling for slugs, snails, and other pests.

Buy Predatory Slugs

Who said that cannibalism is always a bad thing?

Top down, close up view of a Testacella predatory slug on brown leaf.
Wait! Don’t harm this guy! Meet Testacella of the family Testacellidae, your friendly neighborhood predatory slug working the mean pathways of your garden and eating the bad guys.

Conveniently, the slug species Testacella will eat other slug varieties and reduce your populations.

Use Slug and Snail Bait

Traditionally, metaldehyde has been a highly efficient bait/poison in controlling these pesky gastropods. However, this compound has its downside and affects non-target organisms.

Sluggo slug killer in several different packaging and sizes.

Nontoxic Sluggo® Slug Killer

In contrast, iron phosphate is an organic alternative that is almost as effective as metaldehyde and is nontoxic to other organisms. Sluggo® is a brand that has organic OMRI certification. It is available from Arbico Organics.

Purge These Slimy Fiends from Your Garden

While slugs can be fearsome and voracious foes, there are a number of techniques you can use to protect your cole crops.

Macro shot of a banana slug on brassica foliage.

When these options are used in combination, they can be extremely effective.

Have you succeeded in saving your cabbage plants or other brassicas from slugs? Let us know how you fared in the comments.

And for more ideas, consult our guide, “The Best Natural Methods to Protect Your Garden from Slugs and Snails.”

And make sure to check out some of our other guides covering other brassica pests including:

© Ask the Experts, LLC. ALL RIGHTS RESERVED. See our TOS for more details. Product photo via Monterey. Uncredited photos: Shutterstock.

About Helga George, PhD

One of Helga George’s greatest childhood joys was reading about rare and greenhouse plants that would not grow in Delaware. Now that she lives near Santa Barbara, California, she is delighted that many of these grow right outside! Fascinated by the knowledge that plants make chemicals to defend themselves, Helga embarked on further academic study and obtained two degrees, studying plant diseases as a plant pathology major. She holds a BS in agriculture from Cornell University, and an MS from the University of Massachusetts Amherst. Helga then returned to Cornell to obtain a PhD, studying one of the model systems of plant defense. She transitioned to full-time writing in 2009.

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