There should be drainage holes in the bottom so your plants don't drown. If not, drill some and re-plant with crocks over the holes to stop the compost blocking them.
Vendée - 20kms from Atlantic coast.
"The price good men (and women) pay for indifference to public affairs is to be ruled by evil men (and women)."
If you can see roots at the bottom of the pot they need potting on into a slightly bigger pot and you carry on doing that till they're big enough to plant into the ground - a couple of years - or their final pot. Keep them well fed and wateerd throughout the growing season and, in winter, protect pots from frost so the roots don't get frozen to death.
Throw them out for the birds or put on the bird table, please don't stamp on them Gary - they are food for hedgehogs, birds and perhaps frogs or toads if you have them.
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Please do look up the pruning group of your new clematis here - http://www.clematis.hull.ac.uk/new-clemlistsearch.cfm - so you keep all group 2s and 3s together and treat them as group 3 - hard cut in spring.
Also, make sure you don't have more clematis than your supports or space can manage. Look at their eventual size and space them accordingly.