Can't tell just from the leaves but it definitely needs a bigger pot if you can't plant it in the ground. It will also need a bigger climbing support so it can spread.
If it has to stay in a pot, get one twice as wide and deep and use a good John Innes no 3 compost mixed with about 25% multi-purpose to help with water retention. Plant the clematis 3 or 4" deeper than it is now as this will encourage extra shoots to form and make extra stems and thus more flowers.
The same applies if you plant it out - big hole so you can plant it deeper and add some nutrients in the form of well-rotted manure or garden compost and maybe a handful of fertiliser for clematis, roses or tomatoes.
Make sure you water thoroughly before and after re-potting or planting out and never let it get thirsty in dry weather. In my experience, clematis want to grow but some can take a year or two establishing their roots before they really start to grow up top so be patient and make sure you train the stems along supports or you'll end up with a tangled mess.
Vendée - 20kms from Atlantic coast.
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If it has to stay in a pot, get one twice as wide and deep and use a good John Innes no 3 compost mixed with about 25% multi-purpose to help with water retention. Plant the clematis 3 or 4" deeper than it is now as this will encourage extra shoots to form and make extra stems and thus more flowers.
The same applies if you plant it out - big hole so you can plant it deeper and add some nutrients in the form of well-rotted manure or garden compost and maybe a handful of fertiliser for clematis, roses or tomatoes.
Make sure you water thoroughly before and after re-potting or planting out and never let it get thirsty in dry weather. In my experience, clematis want to grow but some can take a year or two establishing their roots before they really start to grow up top so be patient and make sure you train the stems along supports or you'll end up with a tangled mess.