Answer: Based on your description I am not sure what is happening to your petunias, salvias and lawn. There are many possible reasons why plants can fail to thrive. I would suggest you work with your county extension and/or professionally trained nursery staff to try to trouble shoot those.
Slugs can be controlled by handpicking them at night (drop them into soapy water) or by using one of the slug baits that is formulated with iron phosphate. Read and follow the label instructions.
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