Bonsai Climbing Hydrangea Debbie Newman February 11, 2014 These Hydrangea an. petiolaris have been trained for several years to develop thick heavy stalks, all with very unique character. We recently hard pruned about 15 of them to create an open twisting habit. Most are between 4-6' tall. Hydrangea an. pet. Bonsai Hydrangea an. pet. Bonsai, alt view