The Dawn Redwood project is now over 6 feet tall. There is good fusion at the base but the apex has very little fusion because many of the twist ties have snapped and released the seedlings from their bonds.
Here is a closeup on the other side of the tree. This is where I used a screw to attach the seedlings and it has held them together with pressure that can not be achieved with twist ties. The seedlings have completely healed over the screw and it is not visible. It should not be a problem to have screws completely embedded in the trunk because they are brass and will not rust. Even if they do eventually corrode the trunk will be completely fused by then. A problem might occur when I remove the excess whip of the seedling because I can’t see the screw and I could damage tools in the process.
Next spring I will insert many more screws to tighten up the trunk and apply the needed pressure for fusion.