Answer: When plantings fail over a significant area there is usually a soil related reason. I would suggest you work begin by running some basic soil tests to check fertility and pH levels, then amend the soil as indicated by the soil test results. Also add organic matter such as compost to help loosen the soil and prepare it thoroughly by loosening it down about a foot for a perennial bed.
Always use an organic mulch year round to help hold down weeds, reduce watering needs, and feed the soil gradually over time as it breaks down. Mulch should be about three inches thick.
Next, when you decide what to plant, first analyze the growing conditions: What kind of soil is it (clay based and heavy, or sandy and fast drying, etc.), is it extra wet or extra dry or average, is it sunny or shady and at what time of day, and so on. Then select plants that are suited to those specific conditions.
Using carpet is not recommended. The reason is that weed roots can become entwined in the carpet, it is impossible to work the soil, and the mulch layer is not in contact with the soil so it does not break down and renew the soil as it should. Instead, eventually you have a layer of rotted down mulch on top of the carpet making a great place for weed seeds to germinate -- and wet, heavy carpet to be removed.
If you want to try layering something under the mulch to smother weeds, you could use about five to ten layers of damp newspaper or a layer of damp cardboard. These will break down over time to help feed the soil. If you try this, first cut the weeds off short, then layer your paper to exclude light, then top with mulch. If perennial weeds manage to emerge from that, spot treat with an herbicide containing glyphosate or, cut them off again and recover with paper and more mulch. Eventually you will exhaust the weed. Rake the mulch periodically and mantain it at about three inches thick to prevent weeds from germinating there.
I hope this helps!
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