Question
I got a blue aster from Home depot last week and the cold night weather hurt the plant/it wilted and leaves turned blackish. Do I cut it back and maybe it will regrow. I am in Washington state/I think zone 7

Answer
Hi Terri,
Thanx for your question.  Look at the plant tab and make sure that the plant tab says the aster is at least hardy to Zone 7.  I imagine that it is but if you had an exceptionally cool or frosty evening that would cause the damage (the blackishness sounds like frost damage).  Another thing that could have caused the damage to the leaves is that if the plant were being raised indoors and then was exposed to cold evening temps without acclimatizing it (exposing it to the outdoors for short periods of time over a ten-day period...) the plant would suffer some damage from shock.  Yes, I should like to think you could prune off the damage parts of the plant and it should regrow.  Keep the plant hydrated but not soggy and feed it a 12-12-12 balanced fertilizer following the directions on the package.  I hope this helps.
Tom