Oleander in zone 4 at winter outside has all leaves black or silver (was covered with paper and plastic bags). I planted oleander in zone 4, but It was covered on ground, and all over. Tree looks dead, leaves are black and silvered, some white spots from water on a tree by itself. Is there any way to bring it to life, or it is impossible to keep such tree outside (I don't have any space inside) and give it up? I love this tree! But winter is too harsh here in Michigan.
Oleander With Black Leaves
Certified GKH Gardening Expert
Oleanders are considered hardy USDA plant hardiness zones 8 through 10, but they are sometimes damaged by frost in zone 8. That being said, I think zone 4 might be too big of a stretch for your oleander to survive.
I would recommend reading the following article about cold damaged plants and apply some of the knowledge there. You might be able to revive it, certainly worth a try, but be steeled for the possibility that it won't recover: