My wife and I have an old Victorian house in Texas that features a small pond on the south side. The house has been under restoration for a few years and in the process we dug up a large amount of very nice flagstones, which once served as a stepping-stone sidewalk around the property. We would like to re-use them as a flagstone patio around the pond. Our soil is dark clay. The stones are an average of 3" thick. And we would like to plant some sort of plant between them that one can walk on, such as thyme.

Does anyone have any suggestions as to how to prepare the soil underneath the flagstones? Can the stones merely be sunk into the clay soil? Or is it necessary to build up gravel and sand beneath them for stability?

Thanks!

Paul