A few weeks ago, I posted a list of tips concerning shopping for trees and shrubs. I promised at that time to follow up with a list of shopping tips for annual transplants.
Shop at a well-run garden center. I am leery of big box stores; these days they often offer good quality plants and sometimes at bargain prices, but I have found their care of the plants is often poor. In particular, the staff is usually untrained and often underwaters or overwaters the plants. Either way, such treatment stresses the plants and has a permanent effect of their vigor and health.