How to trim this and when?

[Yard Guy]

 

[evo]

looks like river birch.. Round these parts dormant season or mid summer..

 

[colb]

View attachment 57016

They are often sold as double and triple trunkers, but each is likely from a separate seedling. I assume you're referring to the loopy leader. Cut it at the base or, if you have the ability to follow through, strap it to the upright leader and winch them together to see if they will attain a desireable conformation. Might take years to retrain the tension and compression, or not be possible.

If you cut it at the start of the bend, be prepared for death of the leader, or suckering and a three-year repair. If you're concerned more about aesthetic, cut it at an angle that smoothes the transition of the stem away from the other stem - not in direct opposition to it but at a gentler angle of departure to the side that will allow one of the new suckers to spiral away. If you're more concerned about healing the wound than aesthetics, cut it with less angle or straight across.

You can also replant in full or part, but a new individual may be very different from those that were installed (different cultivar, not the same clone, etc.)

 

[flyingsquirrel25]

Harshly, early and often!

Seriously multi stem river birch can be a big problem when they “grow up”. Structurally a mess. Ice and snow in the winter can cause the permanent bows like the one you have or even just a heavy rain in the summer. The wood is very flexible and tends to stay where it is bent but the unions created by the multi stem are not so flexible with age. The inclusions can be terrible to the point of failure.

Once we start on a RB our recommended cycle is biannually at the very least. Many times even annually until the structure and growth can be overcome (because they can put on more annually than you can reasonably take off in the right conditions).

Harshly, early and often.