Rock Cress seed, Aubretia zone 4, is very easy to grow and tolerant of everything in zone 5. My orange one dies back every winter. The seeds seem to winter-over because it spreads to other places but it's easy to pull where not wanted. I hope the same is true of these colors !
HOT and DRY. Drought tolerant Ice Plant (Delosperma) is right at home along this cement curbside. Few sun perennials can take such less-than-forgiving locations yet still provide months of bloom all summer long.