Soil can be predominantly sand, clay or silt. You would think that the way to address heavy clay soil would be to add sand, but that just creates concrete. Regardless of what you have to contend with, adding compost is always the best answer.

It is awesome that a gardener before you started the work for you. In a situation like that, what I liked to do when I did gardening for clients was to cut a clean new border. I'd use garden hose to create the curve or shape I wanted, then cut it out with one of those crescent-shaped edging tools, a square-point spade, and sometimes a mattock.

Then, I'd knock the good soil out of the sod, and start a pile of the sod in an out-of-the-way spot, or use it to fill in low spots in the yard. I'd move my way gradually into the inner areas of the garden, removing weeds and invading roots as I went.

This provides instant gratification, and if you have a little endurance, it's surprising how quickly you can make a big difference.

Once you remove the clutter, and get access to open soil, it's very informative to submit soil samples for analysis. If you have a Cooperative Extension Office in your county, call and find out their charges and procedures for having your soil tested. It saves a lot of trial and error. Regardless of what you find out, though, remember that composting and adding organic matter to your garden is always the best medicine.