Question
I think my soil is killing my flowers in one of my garden beds.  How much soil should I remove in order to put fresh new soil?  Should I buy potting soil and regular top soil and mix it 50/50?

Answer
Hi Sandra, soil doesn't kill plants.  They may die from toxins in the soil, fungal diseases, insects, improper water, incorrect sunlight, soil compaction, incorrect pH or drainage issues, but no plant wants to die.  The truth is...we kill them by giving them something they did not need, or by not giving them something they want.
If we can rule out toxins (oil, herbicides, etc.# then I would never remove soil, just improve it by mixing organic matter with it.  This loosens your soil, adds depth #which improves drainage) and helps your soil microbes.  
Take a soil sample to one of your local garden centers.  They can tell a lot about your soil from the texture and they can probably test it for you also.  Then they can help you pick the right plants for the location and fix the soil if necessary.  Jim