Answer: Unfortunately, a rock mulch provides an ideal environment for slugs -- cool, moist and dark beneath. Apart from removing the rocks altogether, you will have to make a persistent effort to reduce the slug population in that area. One method that may prove helpful is to rake the mulch in very early spring to disturb the slug eggs. Another would be to encourage toads, birds and other slug predators. Next, by all means avoid evening watering. Finally, a concerted effort at controlling the population would include hand picking in the evening (take a flashlight, squirt them one by one with some ammonia and water or drop them into a bucket of soapy water) as well as traps or baits applied according to the label instructions.
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