Lava stones have a rough surface with many sharp edges.
Therefore, lava rock is supposed to deter slugs and snails.
Lava granules (also called lava mulch or lava grit) should be scattered around threatened plants or spread over a large area in the bed.
Horticultural Lava Rocks | Mixed Granules | Natural Volcanic Stone
Click the image to see the offer on Amazon.
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I have tested in a small experiment whether lava rocks can really deter slugs.
Lava granules | Field trial
To test the effect, I spread the granules in a semicircle and placed slugs in the middle.
Lava granulate was used, which is explicitly sold as a slug barrier.
The slugs were freshly collected from the garden. Among them were some leopard slugs and several Spanish slugs.
The following video shows what happened next—in time-lapse, at about 10 times the speed.
Video: Lava granules against slugs in the test
The video clarifies that most slugs are not very impressed.
They simply crawl over the lava stones without being disturbed.
But you can also observe individual slugs that turn away after coming into contact with the granules and take a different direction.
However, these are clearly in the minority.
Conclusion
Lava granulate was not convincing in the test. It was only slightly to not at all effective in deterring the snails.
Therefore, I cannot recommend this product. This is because the stones are relatively expensive and not worth the effort.
Certainly, lava stones can be used as mulch or added to planting soil. It can help suppress weeds and improve soil health.
It is also good as a drainage layer in flowerpots. The volcanic rock further serves as a heat accumulator and increases the oxygen content in the soil.
Horticultural Lava Rocks | Mixed Granules | Natural Volcanic Stone
Click the image to see the offer on Amazon.
However, there are better alternatives as a mulch against slugs, such as sheep’s wool or sheep’s wool pellets.
I have tested numerous mulch materials, but only sheep’s wool and mint have shown success. Coffee grounds, eggshells, sawdust, etc. have proved almost completely ineffective.
Here is an overview: Mulch against slugs in the test.
Alternatives
To protect individual plants, you can also use slug collars.
For the protection of potted plants and raised beds, copper tape is also suitable and effectively repels most slugs.
More information here: Copper against slugs.
If you want to protect larger beds, you can use slug fences.
It is also worthwhile to introduce the natural enemies of slugs into the garden.
If hedgehogs, birds or insects that eat slugs can be established, then slug infestations can be prevented in the long term.
It is also advisable to cultivate mainly slug-resistant flowers and vegetable plants.
More information can be found here:
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Here, you will find an overview of measures to control slugs and snails.
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Peaceful Slug Control & Plant Protection
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| Snail & Slug Repellent Copper Tape | Adhesive | Garden Plant Cloche | Multipack |
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| or on eBay | or on eBay |
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| Sheep Wool Pellets | Slug Collars | Multipack |
| View on Amazon | View on Amazon |
| or on eBay | or on eBay |
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