Answer: Lava rocks are inert, meaning they will not leach anything into the soil. So I don't think they had anything to do with the death of your plants. However, the rocks can absorb and radiate heat which could cause some stress to your plants. And, if the layer is thick enough, they can divert water and any roots beneath them might not get the amount of moisture they are used to. If you placed landscape fabric weed barrier on the ground before installing the lava rocks, it will allow water to percolate down, but if you put black plastic down over the ground before installing the lava rocks, the plastic can keep the ground too dry and can suffocate the roots of your plants. Hope this information helps you determine just what the problem might be. Best wishes with your landscape.
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