Posted: 20/01/2014 at 16:11
Clematis are very hungry plants so, if you can't plant them in the ground, give them the biggest pot you can. It's a good idea to replenish some of the soil each year but not so much that you distrub their roots. Scrape off a couple of inches and add fresh compost, preferably John Innes no 3. Then give it a good watering to soak the whole pot and let it drain. Clematis are thirsty plants too but don't like being water-logged. Add a top dressing of clematis feed in early spring - available in good garden centres - and keep watered regularly with an occasional tonic of liquid rose or tomato food.
As yours bloom in mid to late summer, you can prune them back to the lowest buds on each stem in late Feb or early March depending on how cold your winters are and what the weather is doing. Don't prune when it's freezing.