Mine has dropped it's leaves every winter for the past 5 years, since I've had it. It didn't leaf out this year until almost June. BUT this year, it didn't lose it's leaves and I have no idea whatsoever why.
Interesting. They seem almost as finicky as BRTs this far north
I currently have 2 sets of salicaria (well 3 sets if the cuttings I planted today strike). I have these 2 and I have two that are smaller but are two halves of the same tree. I had cut the top off above the fat roots to see how the two would develop differently. I have a thread somewhere on those two also. They are grown right next to each other and not so far from these at all times.
The winter after the chop on that set, they both threw all their leaves when brought in. This year they aren't any bigger being in small pots, but they hadn't been disturbed and both kept their leaves.
Correlation does not equal causation...and my sample set is very small. It's just a curious observation and something I'll keep tabs on going forward is all. I put stuff like that in these threads because I'm lazy and don't document my work anywhere else as I probably should.