Rough-hewn stone for tree rings...

[mcclureandson]

...with mortar? I'm not a mason and don't work with stone often so I have a couple of questions. I'm installing three circular raised beds for topiary plantings approx 1' high with a diameter of approx 5'...regular compacted base, same as for walls I assume, but what's the best way to mortar the stone to give it a 'dry-stack' look but with more stability? As much detail on the mortar/mix aspect as possible would be greatly appreciated. I'll be using a Pa. fieldstone, irregular squares/rectangles etc...