I planted the runt of the litter clematis vine last year, because that was the only specimen of Nelly Moser my local nursery had, and I was a total newbie at clematis. I didn't think that straggly sad little thing would live through the winter. I pruned it in early spring, as you suggested, and now it's really taken off, more than doubling its size and putting out lots of new large leaves & 5 buds.

It's currently supported by a tripod of 5' bamboo sticks lashed together, free standing away from any fence. How long will that last as a support?