In many, many care guides, you will read that clematis roots do not like to be disturbed. However, then you read about how folks have successfully moved them from one location to another, and you read that some premium-size growers grow their stock in the ground and dig them for transport each season. I myself have had no issues with plants that have required root trimming on transfer from pots on the patio into the garden. The only caution mentioned by Raymond Evison was to make sure that you use a container that is at least 18 inches wide by 18 inches deep... which, interestingly enough, suddenly was interpreted by many enthusiasts to mean your
planting hole needed to be that big... which is not true! Bottom line, I think you would be okay trimming the roots each season from the bottom of the pot and your plant would still prosper.
For the roses, I know that public gardens down near Orlando noted that roses budded on fortuniana rootstock were resistant to nematodes. I've also found that roses on fortuniana absolutely love our hot/sticky climate. Have you tried any roses on fortuniana directly in your garden?
Here's a link to an excellent article on roses from Leu Gardens (in Orlando)... page 2 discusses nematodes:
http://www.leugardens.org/pdfs...
