Slugs are common garden pests that can cause a lot of damage to plants. They feed on a wide variety of living plants and decaying plant matter. Controlling slugs can be challenging, as their soft bodies make them resistant to many insecticides. Fortunately, there are some weather conditions that can help naturally reduce slug populations.
Hot, Dry Weather
Slugs need moist conditions to thrive. Hot, dry weather causes slugs to dry out, which can quickly kill them. Prolonged dry periods with temperatures over 90°F can significantly reduce slug activity and populations. Drought conditions are especially detrimental to slugs.
When it’s hot and dry, slugs often hide in moist, sheltered areas. You may see increased slug activity in the evening and early morning when temperatures are cooler. But extended hot, dry days will eventually desiccate and kill them.
Places that get hot and dry for weeks or months at a time during the summer see greatly reduced slug issues. The lack of rainfall prevents slug eggs and juveniles from developing successfully. Hot temperatures speed up evaporation, making it hard for slugs to stay moist enough to survive.
Cold Weather
Frigid temperatures can also kill slugs. Most slug species cannot survive being frozen solid for extended periods. Temperatures below 30°F start being detrimental to slugs, and cold snaps below 20°F can wipe out huge proportions of slug populations.
Slug eggs are the most vulnerable to cold. Embryonic slugs inside the eggs cannot withstand freezing. Cold fall and winter weather largely prevents new generations of slugs from hatching the following spring.
Adult slugs can survive light freezes and brief cold spells by hiding in insulated spots. But hard freezes lasting multiple days will eventually kill them. The cold causes extensive cellular damage in slug tissues.
Precipitation Extremes
While slugs need moist conditions, too much rainfall can also damage slug populations. Prolonged downpours and flooding can drown slug eggs and juveniles. Slugs may get washed away by heavy rain or beaten down by pounding droplets.
Extremely dry conditions are even worse for slugs. Lack of rain dries out their environment, leaving them desiccated and dead. Hot weather paired with drought deals a double blow to slugs.
Unseasonable dry spells reduce slug numbers, while excessively rainy periods promote them. Ideal slug weather has regular rainfall with occasional dry days mixed in.
Wind
Strong winds speed up moisture loss in slugs, especially on hot, dry days. Wind pushes warm air currents over slugs, accelerating evaporation. On windy days, slugs tend to stay hidden in moist refuges under wood piles, rocks, plant debris, etc.
Powerful winds during storms can displace slugs. Heavy rain and winds beat slugs down and may blow them into hazardous areas. After storms, slugs may be slow to recover or unable to make their way back to shelter and food sources.
Regular windy conditions dry out slug habitats, damage young slugs, and reduce overall slug activity. Gusty days help suppress slug numbers in the garden.
Salt
Salt is toxic to slugs. Sprinkling salt directly on slugs draws moisture out of their bodies through osmosis, quickly killing them. Areas treated with salt repel slugs.
Salt damages the protective mucus coating on slugs, leaving them prone to dehydration. Excess salt can also poison plants, so it should be applied carefully only in slug hotspots.
Salt loses effectiveness after rain washes it away. Reapplication is needed after heavy rains or watering. The abrasive texture of salts may also help deter slugs from crossing treated areas.
Diatomaceous Earth
Diatomaceous earth (DE) is a powder made from fossilized aquatic algae. The tiny sharp edges of DE shards damage the soft tissues and protective mucus layer of slugs. DE absorbs lipids from slugs’ skin, leading to dehydration.
Sprinkling DE around plants helps repel and kill slugs. It is most effective in dry conditions. After rain, DE needs reapplication to maintain effectiveness. Wear a dust mask when applying to avoid breathing in the fine silica particles.
Over time, DE will also reduce slug populations by preventing eggs from hatching when repeatedly applied to known egg-laying areas.
Beer Traps
Shallow containers filled with beer can attract and drown slugs. The yeasty smell draws them in, and the alcohol intoxicates them. Once in the beer, slugs quickly die from alcohol toxicity and drowning.
For best results, sink traps at soil level and space them every few feet in slug-infested areas. Eliminate other hiding spots nearby so slugs are more likely to enter the traps. Empty and refill traps after rains.
Yeast-free beer can also work but is not quite as effective. The fermented carbohydrates and proteins likely complement the attraction of the alcohol.
Copper Barriers
Flexible copper tape repels slugs. The copper reacts with the slime on slugs’ bodies, delivering a mild electrical shock. Copper’ssharp temperature fluctuations also deter slugs.
Wrap copper tape around plant bases, pots, or garden edges. The smooth surface prevents slugs from crawling over. Regularly clean oxides off the copper to maintain effectiveness.
Small copper pipes stuck upright in pots or garden beds also block slugs. The slippery surface prevents upward crawling. Copper foil sheets laid around plants work the same way.
Coffee Grounds
Used coffee grounds deter slugs in a couple ways. The caffeine is toxic to slugs, eventually causing paralysis and death. The grounds also have an abrasive, rough texture that slugs avoid crawling over.
Scatter wet grounds around slug-prone plants. Focus on applying around the bases and any known slug hiding spots. The grounds will dry out after a few days but can be rewetted with a bit of water.
A barrier ring of used grounds provides ongoing slug protection until washed away by rain. Reapply regularly for maximum benefit.
Eggshells
Crushed eggshells can be used like diatomaceous earth to create a sharp, spiky surface that deters slugs. Both the jagged texture and calcium repel slugs as they crawl over the shells.
Scatter crushed shells around plants, particularly seedlings that need extra protection. Focus on creating a barrier around the stems right at soil level. Refrefresh the shells after rain or watering washes them into the soil.
Whole eggshell halves can also be partially buried upright around plants as mini slug fences. These last longer than crushed shells before needing replacement.
Wool Pellets
Sheep wool pellets are made from lanolin-rich wool waste from textile production. The wool fibers slowly absorb and hold moisture. When spread as mulch, the pellets help maintain consistent soil moisture.
For slug control, wool pellets reduce eggs and juvenile survival by absorbing excess moisture during wet weather. This helps prevent rapid slug population explosions when conditions are ideal.
The pellets also slowly dry out the top layers of soil during hot, dry spells. This reduces protective moisture for slugs, forcing them to burrow deeper or risk desiccation.
Natural Predators
Promoting populations of slug predators is an organic control strategy. Common slug eaters include:
- Ground beetles
- Fireflies
- Frogs and toads
- Snakes
- Turtles
- Birds like ducks, chickens, and songbirds
- Opossums
- Moles
- Raccoons
- Foxes
Avoid killing beneficial predator animals that frequent your garden. Provide habitat like brush piles and water sources to attract insectivorous wildlife.
Let chickens or ducks forage in the garden to feast on slugs and eggs. Their scratching also exposes hiding slugs to dry conditions.
Trapping Boards
Placing boards and wet cardboard on the ground attracts daytime slug shelter. The slugs gather underneath, leaving them exposed for harvesting.
Set traps along slug trails in moist, shady areas. Lift to hand pick slugs daily and drop into soapy water. Scrape off any eggs laid beneath to prevent future generations.
Wet corrugated cardboard makes an effective disposable trap. Remove and replace with new cardboard as it gets filled with slugs and eggs.
Nematodes
Beneficial parasitic nematodes can be purchased to control soil-dwelling slugs. The microscopic roundworms attack and kill slugs but are harmless to plants, pets, and people.
Water nematodes into moist soil and repeat every few weeks according to label directions. They are most effective in areas with proper moisture and do not work on dry soils.
Different nematode species target slugs at varying stages, so use a combination to reduce all life stages. Nematodes perish quickly on hot surfaces, so apply only to shaded, protected areas.
Barriers
Physical barriers prevent slugs from reaching plants. Materials like copper, diatomaceous earth, sand, crushed shells, and wood ash create effective blocking perimeters.
Extend barriers an inch or two outward from planted areas since slugs can stretch over short gaps. Keep edges thin and vertical to deter crossing.
Any coarse, abrasive substance slugs dislike crawling over can be applied in bands around garden beds or individual plants. Avoid organic mulches like bark or straw that shelter slugs.
Traps
| Trap Material | How It Works |
|---|---|
| Beer | Slugs are attracted to the yeasty smell but end up dying in the alcohol solution |
| Boards | Slugs gather underneath propped up boards where they can be collected |
| Wet cardboard | Provides cool, moist shelter for slugs to aggregate under so they can be disposed of |
Population Control Methods
| Method | Effect on Slugs |
|---|---|
| Hot, dry weather | Causes lethal dehydration |
| Cold snaps | Freezing damage kills slugs and eggs |
| Salt | Osmotic moisture loss; disrupts mucus coating |
| Diatomaceous earth | Cuts slugs’ bodies, leading to dehydration |
| Predators | Eat slugs and eggs |
Conclusion
Slugs require moist conditions to survive. Hot, dry weather causes lethal dehydration in slug populations. Prolonged cold snaps below freezing can also wipe out slugs and eggs. Heavy rains may drown or displace slugs, but excessively wet weather promotes population growth. Chemical deterrents like salt, diatomaceous earth, and coffee grounds can desiccate and kill slugs. Traps and natural predators help control slug numbers. Using multiple slug control methods together provides the best results.