Most clematis varieties can be grown easily and successfully in a large pot on a patio.
The pot should be a minimum of 45 centimetres in diameter and depth. Avoid evergreen clematis, such as Clematis armandii, in containers because (except in sheltered coastal locations) severe winter temperatures without ground protection can contribute to root damage.
Consider planting two varieties with different bloom times in the same pot. However, be sure to choose varieties with the same pruning requirements, as when it comes time to prune, your plants will have grown together, and it will be virtually impossible to determine which variety is which. Two varieties that will work well together are 'Nelly Moser' and 'The President.' Once established, this combination will provide blooms from April through September. A potting soil that contains a high percentage of coarse peat moss will provide adequate drainage and sufficient water-holding capacity.
For good nutrition, apply a well-balanced slow-release or liquid fertilizer at a moderate to high rate. Allow your container to dry down between waterings. Constant wet feet can create an ideal environment for unwanted fungus such as Aschocyta (clematis wilt). To encourage your plant to grow along your railing, attach a few runs of wire, fishing line or sweet pea netting to give it something to grab onto. Related link: Video on pruning clematis.