
Weak-wooded and fast-grown, mulberry sheds limbs in ordinary summer thunderstorms and splits at the tight forks it forms growing unpruned in a fence line. Because virtually no yard mulberry was ever structurally pruned young, the standard ice or wet-snow failure is a codominant stem splitting out at the union, and the split usually runs far enough down the trunk that what is left is not worth keeping.
If it is being kept, prune in full dormancy, roughly January through March — mulberry bleeds heavily from late-winter and spring cuts once sap is moving. The trap is regrowth and wound response: it answers any pruning with a flush of vigorous water sprouts so a "just get it off the roof" job is back within two seasons, and cuts much over 2 inches on mulberry do not close and rot inward from the cut face.