Will you be spacing the 2 clematis far enough apart that they won't be growing together? The Guernsey Cream is a pruning group 2, it will bloom on the old wood in the spring if not hard pruned. The George Jackman is a type 3 pruning group which blooms on new wood only and is cut back hard every spring. If they grow together it is a nightmare to hard prune one and not the other. If given space apart then yes that would give you a long bloom time. The GC would bloom in the spring and the GJ would bloom in the summer.

I thought MGJ was a 2, but don't have time to look it up now, work calls.

Marie

Uh Oh, I might have read it wrong but either way you raise a good point, flower fan. I am no expert on clems so I don't even know if my idea will work.
My plan IS to have 2 similar clems white/yellow large flower group growing together but get one that flowers early and late and one that flowers during summer so that at least one or the other would be in bloom at any given time from June to September.
If I DIDN'T cut back the Group 3, it is my understanding that it would end up woody at the bottom and all the flowers at the top. Is this correct?
Do you still think my idea could work if I chose different selections or am I out of luck?

enjoy