What is the best season for bending cherry and crabapple trunk?

[proninyaroslav]

Hello everyone. I have some mahaleb cherry and crabapple seedlings and want to give their trunks a dramatic shape while they are still flexible. What is the best season to do it: in spring or early fall?
I live in a fairly cold climate, the temperature in greenhouse can drop to -5C. Heavy bends create micro wounds, will the tree have time to heal them before December, if it’s done in September?
I’m also considering doing it in the spring, but this is a period of strong sap flow, maybe it will be difficult to do it on mahaleb cherries and crabapples, or I’m wrong?

 

[leatherback]

DoIng it in fall, around leaf drop works well for crabs. I stell have to see any branch on a crabapple drop but.. I am not in 5a. -5c is not an issue with them.