Hi Jesse,
to the NGA.
You have a good bit of nice real estate to cover between your flagstones. That would make a lovely sedum, semp and thyme garden area.
Your conditions in CT. are very similar to mine here in Illinois.
Lynn's suggestion of Pediumus spurius is a good choice. I have some but in my climate the harsh winters they are only semi evergreen dying back to the stolons and coming back with vigor in spring.
For low growing I might suggest Sedum Album. Hardy, evergreen, low growing clumping type. It will spread but slowly. Cuttings root up easily for propagation and comes in many different cultivars.
Another good variety, somewhat taller growing but would look nice back against your retaining wall is Petrosedum rupestre subsp. rupestre 'Blue Spruce. I love the bright blue and the spruce needle like leaves. Tough as nails, evergreen, mine seldom gets taller than 6-8". It will spread slowly and is easily propagated from cuttings. I have some of this in hanging baskets, poor soil, harsh sun, rain, snow, ice storms, BAH! can't touch this. Grows equally well in ground. If it gets too lanky for your tastes, wack it back, root up the tip cuttings and it the original plant will produce more branches and come right back.
Another pretty mounding type is Sedum hispanicum 'Blue Carpet'. Winter hardy, slow growing creeper, soft blue in summer, taking on a deeper blue/pinkish blush in winter. The mounds tend to limit themselves to roughly 8-12" in diameter but it also grows easily from cuttings if you want to spread it around or enlarge the area it occupies.
Of the different succulent nurseries listed here at NGA. (Thanks Lynn) Perennial Obsessions has a very nice variety of sedums.
https://perennialobsessions.co...
