Slugs are a common garden pest that can quickly damage plants by eating holes in leaves, flowers, fruits and vegetables. As slugs have soft bodies, they are vulnerable to desiccation and prefer moist environments. This makes them a challenge for gardeners to control in damp conditions that slugs thrive in.
A traditional method used to deter slugs is spreading crushed eggshells around plants. The idea is that slugs dislike crawling over the sharp, gritty texture and will be repelled. But does this home remedy really work or is it an old gardener’s tale?
Do Eggshells Physically Deter Slugs?
There is some basis to the theory that eggshells provide a physical barrier against slugs. Slugs have soft bellies that can be cut and injured by sharp debris. Spreading materials like crushed eggshells, diatomaceous earth or coffee grounds around plants means slugs have to crawl over an abrasive surface to reach foliage.
Research has found that slugs show aversion to crawling over dry, granular materials. The texture irritates their foot mucus and poses a risk of injury. In lab studies, slugs placed on a half eggshell barrier took longer to cross over to the other side compared to a clear plastic surface.
However, in the real world eggshell effectiveness depends on several factors:
- Spreading a dense, several inch deep layer of crushed eggshells is more likely to deter slugs than a light sprinkling.
- The coarser and sharper the egg shell pieces, the more uncomfortable it will be for slugs to slither over.
- Eggshell barriers need to be refreshed after rain or watering which causes them to break down.
- Slug behavior varies by species with some more motivated to push through eggshells than others if hungry enough.
There is also the issue that eggshells primarily deter slugs from crawling over an area but do not stop them from dropping down from above. For plants like lettuces and seedlings, slugs can still fall onto the plants from border walls and high foliage.
Do Eggshells Repel Slugs Chemically?
Aside from the physical barrier, there are claims that eggshells repel slugs chemically due to releasing calcium carbonate as they degrade. Gardeners have reported seeing slugs changing direction before crossing eggshell barriers, suggesting a chemical repellent effect.
Research to date has not found strong evidence to support eggshells repelling slugs through chemical secretions. In laboratory choice test with different materials, slugs did not show significant aversion to containers of eggshells or crushed eggshell secretions.
While there are reports of eggshells repelling slugs when freshly crushed and damp, this effect appears to diminish quickly rather than producing an ongoing chemical deterrent. More research may establish if any initial chemical release from eggshells has slug repelling properties.
Are There More Effective Slug Deterrents?
While eggshells can provide some slug control, there are more effective options to deter slugs based on research evidence:
- Copper tape or foil barriers – Slugs receive an electric shock from contact with copper, causing them to recoil.
- Diatomaceous earth – The razor sharp remains of algae physically lacerate slugs, leading to lethal water loss.
- Coffee grounds – Caffeine is toxic to slugs, but a very high concentration needed for lethality.
- Seaweed mulch – Salt content deters slugs and mulch dries the soil surface.
- Wool pellets – Abrades slugs and retains moisture to reduce environmental appeal.
- Slug hunting – Hand picking slugs at night or trapping under boards or in beer traps.
- Encourage natural predators – Ground beetles, frogs, toads and birds eat slugs.
While more effective than eggshells, many of these methods also have drawbacks. Copper strips can be expensive, diatomaceous earth needs reapplying after rain, coffee grounds may affect plant growth, and encouraging predators can bring new problems.
Should Eggshells be Used in an Integrated Slug Control Plan?
Eggshell barriers can deter some slugs from crossing over and reaching foliage. However, limitations on effectiveness mean they are best used to supplement other more reliable slug control measures as part of an integrated pest management plan.
Advantages of including eggshells are that they are inexpensive, safe for pets and plants, and make use of kitchen waste. Working best in dry conditions, eggshells can be deployed:
- Around seedlings and transplants most vulnerable to slug damage.
- Around the base of established plants to hinder slugs climbing up from the ground.
- Along garden borders and walls where slugs enter from.
- In a ring around vegetable gardens, flower patches and containers.
For best results, use eggshells in combination with trapping, hand removal, predator encouragement and other tactics targeting different elements of slug behavior and lifecycle.
How to Use Eggshells Effectively:
To maximize the slug deterrence from eggshells:
- Rinse eggshells and allow to dry before crushing to get rid of egg residue that can accelerate decay.
- Crush shells into small 1/8 inch or smaller pieces using a mortar and pestle or by grinding in a food processor.
- Apply a band of shells 2-3 inches thick and 2-3 inches wide around vulnerable plants.
- Reapply after rain or watering washes shells into the soil.
- Combine with other organic materials like crushed seashells, wood ash or lime to create texture.
- Replace with fresh shells every 2-3 weeks as they decompose.
The Bottom Line:
Eggshells can provide a measure of slug control by acting as a physical barrier, but have limits to effectiveness compared to other methods. As part of an integrated pest management plan eggshells are a suitable addition, especially for organic gardeners, but should not be solely relied on to protect plants.
With careful placement around vulnerable plants, refreshing after rain and combining with other tactics, eggshells can be a worthwhile addition to the gardener’s arsenal of slug deterrents.
| Advantages of Eggshells | Disadvantages of Eggshells |
|---|---|
| Cheap and readily available | Not as effective as other methods like copper tape or diatomaceous earth |
| Organic and safe for children and pets | Need reapplying after rain or watering |
| Make use of food waste | Can wash into soil rather than staying as a barrier |
| Abrasive texture deters slugs from crossing | Slug species vary in eggshell tolerance |
| Provides some repellent when fresh | Does not prevent slugs falling from above |
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