Answer: The first question is what chemicals did the lawn service apply? If they are of the type such as preemergent herbicides that breaks down quickly in the soil, then you can plant in that area this spring. Find out this piece of information first, before you build a raised bed. If you want to build the bed, laying the plastic on the soil and building up is fine. For vegetables the bed should be at least 10-12" deep. filled with loamy topsoil amended with compost. Let me know what chemicals the lawn service applied and maybe I can help you determine whether you have to build the bed.
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