Posted: 25/07/2012 at 11:25
It's a bit late to prune them now but you could give them a feed of special clematis food and an instant tonic of liquid tomato food to encourage growth and flowering. Come September, give them a sprinkling of bonemeal to encourage root production.
I'm assuming you planted them at least 4 inches deeper than tehy were in their pot. If not, it may be worth digging them up after a generous watering and replanting at the proper depth as this helps keep their roots cool and encourage the formation of new shoots.
Next spring in Feb or March, depending on the weather, give them a good feed of general fertisliser such as blood, fish and bone or pelleted chicken manure and a liquid tonic of rose or tomato food. That will encourage good roots and foliage. Then feed regularly with clematis food from spring to mid summer.
The Montana should only be pruned when it gets out of bounds and then only after flowering is over. The tangutica, Arabella and Jackmannii should be pruned back to the lowest pairs of buds in March as they regrow each season and flower on the new shoots..