What time of the year to I trim a Japanese willow ?
The heavy annual pruning is done is early spring. Take about 1/3 of the oldest branches to the ground. This spurs new growth which is more colorful than older growth. Since it is a vigorous grower, you may need to trim the bush in June and again about now to keep it from getting too tall. Notice the difference between trimming and pruning. Vigorous growing shrubs need both.