Answer: It's more likely that the plants in question are annuals and they have finished their lifecycle, which is why they are dying off at this time of year. Some perennial plants die down naturally in late summer as well, but return the following spring. Without knowing specifically which plants are acting this way in your garden, I can't tell you whether the process is normal or something to be concerned about. If you submit another question through the Home Depot forum with the names of the plants in question, we can offer more information.
Best wishes with your garden.
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