Clematis The President' belongs to the Large flowers clematis family and has full purple-blue flowers. It flowers twice a year and therefore adds a nice touch to your garden. The first flowering is around May-June and the second flowering is between July and September. After the clematis has flowered for the first time, it is best to prune it back so that it will flower again for the second time. Its neat and compact growth makes this climber suitable for both large and small gardens.