Hi everyone, I have this smaller tree in a tight spot near the back of my house that was planted before I moved here. I’m trying to identify it, and I’m also wondering why it has two separate “trunks” with one having only green leaves and the other having burgundy? Any information will gladly be appreciated.
It's Albizia julibrissin 'Summer Chocolate', common name chocolate mimosa. It is usually grafted onto the usual green-leafed species. So one possibility is that the green leaves are from the rootstock - does that trunk start from below where the burgundy leafed trunk starts? Or it seems that some of those trees just do have some green leaves, as appears on the burgundy trunk. If you scroll down on this page: danger garden: Albizia julibrissin 'Summer Chocolate' – observations, you can see a plant at a nursery that is doing that. However, since the one side is entirely green, I would expect it to be rootstock growth. I'm really only familiar with grafting scenarios on cherry trees, on which leaving the rootstock growth will usually let it completely obliterate the fancy cultivar that was grafted onto it. An arborist should be able to tell you if the chocolate cultivar will be ok if you remove the green trunk. Or even if you leave both, whether they will each be able to go their own way and co-exist.
I respectfully disagree with leaving two trunks. While the hort industry loves to graft this on that, there are long term problems that begin to occur well after the warranty wears off. Usually, or often, the reason for grafting is to speed up the growth of stuff that grows slowly on their own roots to get to market earlier. When a slow growing top can't keep up with the energy flowing from the rootstock, you get suckering. If you regularly prune the top to shape or keep compact, you get suckering. If the top gets winter-killed you get lots of suckering. If the graft is not intentionally "pretty", they can get very prominent. Even if done well, exactly where the graft is, is important. A weeping cutleaf Japanese maple high on an aggressive-growing standard can have a perfectly round ball just below the graft interface. It is unattractive, in spades. There are even worse eventualities, like in tree peonies which are mostly grafted on herbaceous rootstock. You always prune for removing winterkill, but never root prune to balance, so eventually the rootstock will become so out of proportion that the evil herbaceous stalks emerge... with a vengeance. You need to prune them out weekly, or else the woody portion will grow too poorly to survive and build buds for next year. Alas, Tree Peonies on their own roots are really expensive. If you leave the green trunk and the chocolate trunk, the green will probably outgrow the other PDQ and ultimately shade it into slower under-growth and someday the chocolate will disappear completely. There are two solutions, neither easy nor absolutely successful. Lop off the green one after it has used up the energy of leafing out in spring and then root prune a complete 360° circle ~16 to 20" out from the trunk, one spade deep. Keep watch for sucker buds that will probably follow and nip them forthwith. Never let them leaf-out. You may find suckers outside your circle. That is now a "rooted cutting" and you need to dig that whole root out because it will take forever to kill one nip at a time. If you keep root pruning yearly or more, eventually, maybe, possibly, the top might get to the point where it only produces enough energy to support the chocolate rate of growth. Don't bet the farm on it. The other alternative is to remove the green growth, dig it up, root prune to balance the top and roots, and replant. Root prune with a shovel as above until green buds disappear forever. Buy new shovels as necessary.
