Stepping Stones can be placed directly on the membrane. For a more secure hold, you can add a layer of landscaping sand before placing the stones. Other Stones it depends on the type of stone and desired look, you might need a layer of gravel or sand under the stones.
I wanted to ask:
Do you have any specific plants in mind?
Do you have any budget constraints?
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craigslist landscaping jobs' on platforms like Craigslist or AroundWire and specialists will start contacting you.