Clematis sieboldii (Clematis florida var. sieboldiana) is a striking vine that bears white flowers with a purple center. It will quickly clamber over a fence, wall or trellis to provide color in the spring and summer garden. All clematis require pruning to keep them in the framework you’ve chosen and to promote blooming. The time to prune, and the method, depends upon the type of clematis. The Florida group, of which sieboldii is a member, flowers on stems that grow from one-year old wood, so you should prune them immediately after flowering.