A common question we see relates to what to do (aside from cut down and dig out) when a JM breaks under load, that is snow, ice, or wind. This kind of break usually happens around a narrow 'V' crotch branching. These narrow branchings are quite weak, so sometimes people recommend using formative pruning to avoid them. None the less, they make for an attractive looking tree. The tree here is an Acer palmatum selection from a 2010 seedling, very vigorous with excellent and long lasting fall color. A fine landscape tree, nothing out of the ordinary really. It broke in a recent snow storm, with very heavy wet snow. The procedure is: 1. remove as much weight from the canopy as possible, to leave a good form 2. cinch the tree as tightly as possible 3. drill bolt holes all the way across, use a plastic or rubber washer under the metal washers. 4. insert and tighten the bolts from the bottom up I decided 3 bolts would be enough, but the top one actually broke from the weight -- the tree is probably 5m tall -- even though it was a 6 mm steel bolt. You can see the broken bolt stuck into the gap in the 3rd pic. So I had to redrill the top hole for an 8 mm bolt, which then held, as you see in the final picture. I'll cut off the extruding bolts once I get my Dremel back from the guy I lent it to, and it will look less like a Frankentree. The tree will easily compartmentalize the damage from the drilling, and as the trunk grows, the gaps will pleach back together. Eventually, the bark will grow around the bolts themselves.
I would leave out the top pruning. Trees are integrated systems just like us, their leaves make food from the sun part of which is transported to the roots and stems. So that top pruning reduces stem growth.
I agree in principle, but there was just too much weight. I think it should be kept to a minimum, but sometimes unavoidable. Agree, taking off some limbs will set it back some, slow it down, but it still kept a nice form. No topping! haha.
In case both forking stems are with similar diameter and growing speed, they would not merge properly, as they grow. The picture from POP Pruning Guide: Fruit Trees – Philadelphia Orchard Project explains:
I'm thinking that it would be good to put a couple of eyelets at roughly the level of the top of your first photo, @emery and hook them together with a turn buckle (or a loop of wire equivalent). yadda, yadda, yadda
I love v-shaped trees despite their inherent weakness in snow. Luckily we rarely get heavy snow here. 6mm bolts are not very strong in construction terms, no surprise it broke. I would be tempted to up the remaining 6 millers to 8mm too. Or probably better, just add another 8mm inbetween the top 2 bolts. If that trunk gets flexing in a big windstorm they are going to be under a lot of strain! More interestingly, how did the broken bolt get to where it is in the picture? And I agree that some weight reduction in the canopy was/is needed in this situation, needs must and all that....
I actually considered putting in some lower bolts each with a 30° angle or so, which if I remember freshman physics would help resist torquing. But the truth is, I've moved deep into pruning, already with a lot to do and already seeing some bleeding. Really early for it, so trying to finish by year's end. And I just found a largish oak that lost it's top, so there's another big job to do, luckily there is an alternate leader available. Which means this project is finished, at least for this year. The answer to the second question is: sleight of hand! I picked it up off the ground, and stuck it in the crack, demonstrative-like. ;) P.S. I didn't wait to stratify my Australian pentaphyllum seed, more fool I. They are germinating like crazy now, I've moved the tray onto a windowsill inside. Will probably shuttle in and out a little, if the weather is acceptable, but the polytunnel will freeze a bit, which would kill them for sure.
Why not to use some wood glue as the first step? The old xylem is dead and does not merge by itself even if tightly connected and under pressure.
Well, there are a few things here. If the repair is done soon enough, and the break is clean, the bark will join and graft, just like any veneer graft. In this case, as a week went by, it's unlikely but not impossible for there to be some rejoining. Certainly for an immediate repair of a ripped branch (for example) it is possible to "regraft" by holding it together with packing tape or buddy tape, and then drill and bolt the following year. But sure, you could potentially be very careful to keep any glue away from the phloem. Mind you, the xylem through much of the stem was still pretty wet, so you'd also have trouble getting glue to stick. For the glue, I don't think it would help much for strength, as too difficult to align the sides to get good surface contact, and although I'll grant that modern carpenter's glue is very strong, it's not stronger than the bolts. Not to mention moisture interfering with the cohesion by preventing the glue from drying properly. But further: Dr Alex Shigo spent 25 years and wrote multiple books showing among other things that the introduction of foreign substances in repairing trees is not a good idea, because it interferes with the tree's natural process of compartmentalization of decay. His work being the foundation of modern arboriculture, I think following his recommendations is pretty much the gold standard.
@emery, there are glues that require moisture to cure --> Gorilla Glue is one branded version. I've used it on ceramic pots and it is quite strong (though holding the pieces in place against the foaming of the glue can be challenging). In this case one would have drizzled the glue into the split before tightening the bolts. At this point, though, I agree that it is probably not worth the trouble. Further, trees will not over-grow punky/rotted wood, such as a large branch 'stub', but it will overgrow almost anything solid = epoxy, concrete, .... I and other bonsai enthusiasts have done this multiple times. Gluing the xylem as @Sulev suggested is no different that gluing lumber (dead wood) chemically and mechanically - it might have added some mechanical strength beyond the bolts, IMHO. Glue may have also provided a seal against water intrusion at the crotch which will foster wood rotting (fungi), though one could put some kind of plastic film or putty of some kind in the crotch (until new bark has formed in it) to accomplish the same end. I don't recall the context in which Dr. Shigo made the remarks you refer to, but the tissues (xylem, cambium, phloem, and bark) exposed by the split all executed (or are executing) compartmentalization. These exposed tissues will never rejoin, excepting possibly the cambium. If the cambium rejoins (as it would with a successful graft), then new xylem, phloem and bark will form across the split. The stem wood exposed by the split will never rejoin as there is no tissue that makes new wood other than cambium (which is a thin layer of 'stem cells' between the wood and bark). In other words, this split will naturally be weak 'forever more'.
I found young penta seedlings grow very well indoors (ie house) under artificial light when sprouted early, and then moved outside in late spring. They didn't seem to mind the extra long growing season, probably helped actually. Merry Chistmas!