You want fast spreading plants with a lot of foliage-fertilize. If you want flowers-do'nt.

Yarrow grows like gangbusters here in our alkaline soils and with very little water. So I wouldn't worry about the pH so much as just having more of a well drained mix, although they have performed more than fine in my heavy, wet, clay soils too. Except for the yellow cultivars that seem to stay more under control, I don't plant them anymore--they are invasive as heck!! Pots are a fine idea for this one.