A large-flowering clematis vine with blooms 5 to 6 inches in diameter, the Nelly Moser clematis bears light pinkish mauve flowers with petals striped in deeper red-pink. Blooming in early summer, exposure to intense sunlight tends to bleach out the petal colours and, according to the "A-Z Encyclopedia of Garden Plants," any reblooming in late summer also yields paler coloured blossoms. Naturally compact, the Nelly Moser clematis matures at only 6 to 10 feet tall and 3 feet wide when grown on a trellis, often not needing much pruning maintenance. This variety of clematis is best grown in fertile, moist and cool soils across U.S. Department of Agriculture hardiness zones 4 through 8a.
Trim back the vines lightly in early spring with hand pruners just before the buds swell and open. Nelly Moser is classified as a Group 2 clematis vine, meaning it blooms on new growth that sprouts from buds set the previous year. Therefore, in early spring, focus on removing only dead or broken vining branches. Make the pruning cut 1/2 inch above a lower dormant bud or branch junction. The Missouri Botanical Garden mentions that no annual pruning on Nelly Moser is required to grow well and flower nicely.
Cut back overgrown and dead vining stems in early spring to a height of 6 to 12 inches if your winters are harsh or the vine has grown wildly and looks unkempt. According to the University of Illinois Extension, this severe pruning causes the Nelly Moser clematis to not flower in early summer, but will grow vines that mature in time to bloom in September or October.
Trim the new growth on the vine across early and midsummer to keep the plant in an overall tidy size and shape. If flowering occurred in early summer, prune back stems after the flowering ends. This should be all the pruning needed as it will again flower early next summer. You may get some flowers on the tips of vines in September and October on new vining stems not pruned after the main early summer flowering display.
Do not tip-prune any new growth on the clematis during the summer if you conducted the harsh pruning in early spring. You'll end up removing possible flower buds for that autumn.