Answer: Clematis usually benefit from some annual pruning, perhaps this would help yours as well. The following web page provides pruning guidelines as well as general care recommendations for clematis.
When you select plants for landscaping an area, you need to think about the mature size of the plants later on when they have had time to grow to their full size. Be sure they will not crowd each other when full grown.
You also need to consider the overall effect you are trying to achieve. Often, it is more satisfying from the design sense to limit your plant pallette to just a few plants and then repeat the same plants for continuity. If you add many different types you can sometimes end up with a hodge-podge that seems visually cluttered.
Too, a formal setting usually calls for straight lines and a lot of repetition. An informal setting allows more leeway in plant selection but still requires balance and proportion to the plantings.
I suspect if you are wondering if more will be "too much" then it probably will be, although certainly it is a matter of personal taste.
I hope this helps!
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