Fertilizing: Clematis are heavy feeders. Amend the soil at planting with compost. Each spring add a 1- to 2-inch layer of compost around the base of the vines and a balanced organic fertilizer with a 3-1-2 ratio of nitrogen, phosphorous and potassium. Side dress again in early summer.
Mulching: Clematis should be mulched annually in the spring to keep the soil moist and prevent weed growth. Use an organic mulch, such as bark mulch, but keep it 6 to 12 inches away from the stems to avoid wilt disease.
Trimming & Pruning: Spring and early summer-blooming clematis should be deadheaded after flowering to encourage more blooms to form next year or even later in the summer. Late summer and fall-blooming types don't require deadheading. In fact, the wispy seed heads are an attractive addition to the fall and winter garden.
All vining clematis should be pruned each year. Pruning clematis can be confusing since it depends on the type of clematis you're growing. The first step is to always prune out dead, diseased and broken stems any time during the growing season. Wait until it's clear which stems are alive and dead in spring before pruning.
Prune based upon the bloom time. For clematis varieties that bloom in spring and early summer on old wood (second year), prune after flowering. For varieties that bloom in summer and fall, prune in spring since these varieties bloom on new wood. Spring pruning will stimulate more growth. For large-flowered hybrid varieties, deadhead spent blossoms after the first flush of flowers. A second flush will occur later in the summer.
When pruning new clematis vines, prune back the vine to about 1 foot from the ground to stimulate branching lower on the plant. As it grows in the first year, pinch the growth tips periodically to force more branching. This will eliminate flowers the first year, but create a multi branched plant that will produce more flowers in the future.