Answer: Most of the colorful hybrid clematis mature in the 8 to 12 foot range, so you would not want to put them too close together, maybe four feet apart or so at a minimum. If you use a variety that reblooms on new growth during the summer, you would have some color later in the season on just one vine. If you plant two types side by side you would probably want to use varieties with similar pruning needs in case they become intertwined.
With pink hydrangeas, I personally would use a purple, blue or white clematis, only because pinks can be difficult to blend. Your local professional nursery staff should be able to show you a selection.
The sweet autumn clematis is a much larger vine with small but fragrant white flowers in the fall. It dies back during the winter and is pruned off very short in early spring each year. Then it regrows very quickly to as large as 20 feet or more. This may be too big in a mixed border or flower bed situation.
I hope this helps.
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