Mountain Ninebark 'Grey Rock'Mountain Ninebark 'Grey Rock' (Physocarpus monogynus) is a rugged, handsome native naturally occurring cultivar from the Cache la Poudre Canyon, Colorado. Its peeling, cinnamon brown bark reveals layers beneathhence the name ninebarkand adds texture and winter interest long after its white spring blooms fade. In late spring and early summer, clusters of small, creamy white flowers brighten rocky slopes and dry hillsides, giving way to seed capsules