Clematis montana is a vigorous climber that is perfect for covering large supports such as pergolas or walls. From late spring to early summer, it is a sight to behold as it becomes covered in white flowers. Like all early-flowering clematis, it requires little pruning other than the removal of any dead or damaged growth after flowering. Large plants make suddenly die off for no apparent reason. This is usually due to a condition called slime flux. This is caused by an injury to the stem early in the season. The sap leaks out becomes infected with bacteria. Cut out infected stems, pruning back to good wood even if this involves going down to ground level.