Answer: Clematis are tricky to grow in the south. As you indicated, they love to have their roots mulched to keep them cool. They also appreciate some mid day to afternoon shade. That blazing summer sun may be your problem. The best looking clematis I have seen in southern gardens are peeking out of the edge of the woods bordering a lot. They appreciate morning sun but by noon...well, you know, we're the same way!
It is good that you have one of the types that bloom on new wood. The fact that they are coming back each year is also good news as it indicates the problem is not drainage.
Make sure your plants are getting plenty of water, but don't overwater. Don't overfertilize either, they'll resent it!
Check the leaves that start to lose green color for spider mites. If they are present, try spraying plants from beneath the leaves with a strong blast of water to dislodge these pests. Doing this every 5 days or so can help keep them in control. Spraying with a product containing neem is another organic way to fight mites.
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