Caring for Delphinium Aurura Blue
How to care for, prune, maintain and winterize Delphinium (Aurora Blue).
After your delphinium has finished blooming cut off the flower stocks. If it blooms early enough and you do that you may get a second bloom in late summer. In the fall trim the entire plant back to the soil. I live in a zone 3b & mine survive fine with snow cover from mother nature. You could put a mulch of dead leaves over top. It is important to prune it down in the fall preferably after the frosts have mostly killed the foilage. This procedure helps to prevent delphinium worm infestations.
Hope this helps you out.