There is not need to trim the roots of your angel's trumpets. They need morning sun and afternoon shade and require frequent watering as they'll wilt anytime they are subjected to the sun for a period of time on a hot day. They will probably not be perennial in your climate as the winter cold is too intense. You'll want to bring them in for the winter season.
I am not aware of local sources for the blue fanflower. Check with a local garden center and see if they can direct you to a local source.
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