Winterberry aren't fussy about when they're pruned back and how hard; I work at a nursery and we cut ours back several times a year. Our stock is usually kept at 3' or so but if we have some that developed an irregular shape we'll take them down to a foot. They're quite tolerant
Comments
Prune in mid late March
Prune out 1/3 of the oldest thickest canes
And interfering branches
Jon Cholwek