I agree that the spray n grow may be causing the black leaves. Also cold temps will do that. It must be so difficult growing plumerias in the northeast. I love them so much that I to would try an grow them anywhere. I know how you feel having to bring them in at night because of the cold temps. I have 25 new cuttings that I had from late last summer and from early this February. I had to bring them in every night because the night time temps would dip below 50 degrees. I know they can stay outside and survive those temps but it's way better if they stay warm at night when they are that young. I couldn't imagine living somewhere where it snows or where the temps dip below freezing. So I give you a lot of credit enjoying your hobby while living in New York.
