The Clematis montana ‘Grandiflora’, I planted this spring is healthy, but one stem grew to 6 to 7 feet while a couple others at the base are only a foot long. To encourage denser growth, should I have been pinching it back throughout the summer? To get thicker growth next year what should I do now (if anything) and next spring?
Probably the most frequently asked question about clematis concerns pruning. Clematis are generally divided into three groups for pruning purposes. Your Clematis montana falls into Group A, which includes spring-flowering varieties whose flower buds were produced during the previous season. Therefore, any growth that is removed between late autumn and early spring will cause that much flower loss for the coming season. So, any pruning that you want to do to control the plant should be done in early summer. I wouldn’t be too concerned about encouraging dense growth, however, since Clematis montana is an extremely vigorous grower.
For your information, Group B varieties also bloom on the previous year’s growth. The recommended time to prune is February or March to remove weak and dead stems. The remaining stems are cut back to just above a pair of good green buds.
Finally, Group C consists of these Clematis that bloom only on new growth. Pruning these varieties involves cutting back all of the previous season’s growth to a pair of good buds usually about 10 to 12 inches above the ground. This should be done in February or March.