Posted: 24/06/2014 at 18:22
All you can do is keep it watered and hope. There was a late frost here which killed all of the leaves and flowers on 4 of my young magnolias. The ones which were planted 2 years ago have now recovered and grown new leaves but the two planted last Autumn are dead sticks and have now been pulled up.
Use your thumbnail to scrape a small amount of the outer bark from the trunk, starting at the top. If it is still green underneath they are alive. If brown, the wood is dead at that section, so move down a few inches and try again. If brown all the way down there is no hope of recovery. If you do find green tissue, cut all of the dead wood above it off, just above a bud if you can see one.