Slugs are a common garden pest that can wreak havoc on vegetable gardens, flower beds, and other ornamental plants. As slimy mollusks, slugs use rasping tongues to feast on tender shoots, leaves, flowers, and fruits. When slug populations explode, the damage to plants can be extensive, making effective slug control an important concern for many gardeners.
What are some common slug deterrents?
There are many commercial and home remedy style slug deterrents available to gardeners. Some of the most common include:
- Diatomaceous earth – The sharp edges of this powdered mineral physically damages slugs and dehydrates them
- Beer traps – Slugs are attracted to the yeast in beer and will drown after falling into containers sunk into the soil
- Copper tape or copper pipes – Slugs receive electric shocks from contact with copper due to interactions with bodily slime
- Eggshells – The sharp, gritty texture can irritate slugs and damage their soft bodies
- Coffee grounds – The caffeine and coarse texture make movement uncomfortable for slugs
- Salt – Pure salt will dehydrate and kill slugs on contact
There are also many commercial slug bait and pellet products that contain metaldehyde, iron phosphate, or sodium ferric EDTA. Always read product labels thoroughly before using chemical slug baits.
What natural predators help control slugs?
In addition to directly deterring slugs, encouraging natural predators in the garden can help keep slug populations in check:
- Ground beetles – Both adult ground beetles and larvae prey on slug eggs and young slugs.
- Fireflies – The larvae are voracious predators, feeding on slugs, snails, and other small invertebrates.
- Frogs and toads – Slugs make up a large part of the diet of many frog and toad species.
- Snakes – Garter snakes and other small snake species consume slugs and keep numbers down.
- Birds – Geese, ducks, turkeys, and chickens will all eat slugs and can be allowed to forage in the garden.
Creating habitat for these slug predators, avoiding pesticide use, and tolerating some damage can allow nature to help control slug populations.
What physical barriers deter slugs?
In addition to chemical controls, there are some simple physical barriers that can be implemented in the garden to deter slugs:
- Crushed eggshells or diatomaceous earth around plants
- Copper pipe, tape, or mesh around raised beds or containers
- Plastic sheeting or straw as mulch between rows
- Vaseline or petroleum jelly smeared on surfaces
- Sharp grit like sand or crushed gravel surrounding plants
These abrasive textures irritate slugs and limit their ability to move freely to reach plants. Keeping vegetation trimmed away from beds can also eliminate protective hiding spots for the slugs.
How effective are beer traps?
Beer traps are a popular home remedy for controlling slugs. The traps lure in slugs with the scent of yeast and beer, drowning the mollusks in the liquid. To make a simple beer trap:
- Bury a cup, bowl, or jar up to the rim in soil near plants being damaged
- Fill with cheap beer, leaving 1-2 inches at the top
- Optional – Create coverings or lids with small holes to prevent beneficial insects being trapped
The traps should be emptied and refilled every few days as long as slugs continue to accumulate. The effectiveness of beer traps depends on a few factors:
- Proper placement near foliage that slugs are targeting
- Using enough traps to cover vulnerable plantings
- Frequent emptying and replacement of stale beer
- Presence of other food sources that lure slugs away
- Environmental conditions and size of local slug population
When these factors are all addressed, beer traps can provide moderate control, capturing several slugs per trap each night. They may not eliminate all damage, but are a simple option to try.
Should slug pellets containing metaldehyde be avoided?
Metaldehyde is one of the most common active ingredients in commercial slug bait pellets. It is moderately toxic to people and pets if ingested, and there are concerns over toxicity to wildlife. Many gardeners are now avoiding metaldehyde products due to the risks. Safer alternatives include:
- Iron phosphate baits – Much lower toxicity to children, pets, and wildlife
- Sodium ferric EDTA products – Also have very low risk for non-target animals
- Diatomaceous earth dusts – Not a true poison, works by physical damage
If metaldehyde baits are used, the following precautions are critical:
- Carefully follow label application rates and methods
- Never use near edible plants or areas where children play
- Avoid contamination of ponds, streams, or other waterways
- Thoroughly wash hands after handling
- Clean up any scattered pellets after application
Given the potential risks to pets, wildlife, and water quality, avoiding metaldehyde altogether is the safest approach.
Are eggshell barriers an effective deterrent?
Crushed eggshells spread around gardens are often recommended as an easy slug deterrent. The jagged texture and calcium content are proposed to deter slugs in various ways. Research into the effectiveness of eggshell barriers shows mixed results:
- Small observational studies show reduced slug damage to seedlings when encircled by eggshells
- Other trials demonstrate no benefit compared to control groups without eggshells
- Slug movement appears slowed by eggshells, but not completely blocked
- Effects seem dependent on eggshell particle size and depth of layer around plants
A few drawbacks of eggshells are that they break down quickly, require frequent re-application, and can attract other pests like snails. While not the most reliable standalone control method, crushed eggshells are simple to spread and may provide some temporary protective value against slug damage when applied properly.
How do different slug species impact control efforts?
There are nearly 30 slug species that may be encountered in North American gardens. A few of the most common include:
- Gray garden slug (Deroceras reticulatum) – Prolific pest, up to 2″ long
- Marsh slug (Deroceras laeve) – Darker coloration, found in damp areas
- Greenhouse slug (Milax gagates) – Distinctive black with orange slime trail
- Yellow slug (Limax flavus) – Gets up to 4″ long, nocturnal feeder
- Leopard slug (Limax maximus) – Large, up to 6″ long, distinctive spots
Identifying slug species can provide some insight into their behavior patterns and allow for more tailored control strategies. For example:
- Nocturnal feeders like Limax flavus are more prone to beer trap capture at night
- Species living in damp areas like Deroceras laeve can be deterred by improving drainage
- Larger slugs like Limax maximus require stronger barriers and predator pressure
In general, implementing multiple control tactics and maintaining vigilance is key to dealing with any slug species. But noting the key species in your garden and when they are active can lead to more effective management.
Should salt be avoided as a slug deterrent?
Salt is an effective and inexpensive slug killer, as the sodium causes the slugs to dehydrate and die quickly when they come into contact with it. However, salt can cause problems in the garden when used improperly:
- Excess sodium damages soil structure and chemistry over time
- Salt runoff can contaminate groundwater, ponds, and streams
- It may burn and kill plant roots, crowns, and leaves
- Beneficial soil organisms like worms and bacteria are harmed
If salt is used to control slugs, it is best applied sparingly and directly only where slugs traverse. Scattering salt across soil surfaces should be avoided. Only 1-2 teaspoons per square yard is needed. Salt mixed with an abrasive like sand or diatomaceous earth is more effective with less salt required. Heavy rainfall will necessitate re-application of salt barriers.
What environment modifications deter slugs?
In addition to direct control methods, creating an environment less favorable to slugs can be an important part of an integrated pest management plan. Steps like these can make gardens less inviting habitats:
- Eliminate hiding spots by removing piles of debris, leaves, boards, etc.
- Raise planting beds to improve drainage and cut down on moist dark areas slugs prefer
- Use drip irrigation and avoid overhead watering to keep foliage dry
- Clear 3-4 foot diameter areas of vegetation around vulnerable plants
- Apply new mulch after planting rather than before to avoid providing cover
- Group susceptible seedlings together within barriers for protection
Along with directly managing slug populations, executing cultural practices to reduce dampness, hiding places, and access to plants can be an important part of control.
How effective are diatomaceous earth barriers?
Diatomaceous earth (DE) is the powdered remains of ancient sea organisms called diatoms. The microscopic silica particles are sharp and abrasive, causing physical damage and dehydration when slugs crawl across treated areas. Research shows:
- DE significantly reduced slug activity and damage when applied as a barrier around plants in multiple studies
- Effectiveness depends on applying an even layer of at least 1/4″ deep around vulnerable plantings
- DE works best when kept dry, so reapplication after rain or watering is advised
- Must contact slugs directly to work, but has no toxicity risks for people or wildlife
Properly applied as a physical deterrent, diatomaceous earth can provide effective slug control without chemical toxins. DE performance is reduced when applied directly to damp soil though, so maintaining dry barriers is key.
Conclusion
Controlling slugs in gardens require an integrated approach, rather than a single cure-all method. The best results will combine:
- Direct population control via traps, baits, or natural predators
- Physical barriers to protect vulnerable plants, like DE, copper, or crushed eggshells
- Horticultural practices to reduce dampness and hiding places for slugs
- Persistence in monitoring and maintaining defenses against reinvading slugs
With a toolkit containing multiple tactics, gardeners can combat slugs at all stages of their lifecycle. Eliminating favourable habitat and deploying barriers to limit access to prized plants provides the best chance for effective, long-term slug management and protection of backyard or commercial plantings.