Sounds nice. Why not use potting soil? Try and get one without the fertilizer in it. I repotted a jade plant in some of that and it almost killed it. I wouldn't use clay soil. It sounds like you have enough sun. A half a day of sun should be enough.

Water drain well in your flagstone path? That is key for thyme. Skip the compost and mulch if possible. Thyme likes the soil lean.

FataMorgana

Thank you for your replies; I finished the path last weekend.

I filled the spaces between the flagstone with cactus mix; I'll plant the Thyme (or ???) in the fall.

We have Thyme growing elsewhere in the yard, and when I planted it about 10 years ago I amended the soil with plenty of organic matter, LOL, not knowing any better about Thyme. Well, it's still there... a little rangy (could use a haircut)... but it's still growing and seems happy enough.

This time, I won't amend the soil, and most of the Thyme plugs will be growing in the cactus mix.

Also I'm sure you know you need a creeping thyme variety, Thymus serpyllum or similar, or one of its cultivars, rather than T vulgaris, the usual culinary thyme.

flora_uk: Is that because the culinary thyme doesn't like being stepped on? I plan to put that type along the edge of the path, and fill the center area with a creeping time.

No thymes LIKE being stepped on. Just that culinary thyme could be a foot tall and creeping thymes stay flat on the ground. Stepping on the larger plant does more damage and could also trip you up. It would be more like a flower bed than a path. So your edging plan sounds good.