Answer: Left to their own devices, these vines (Campsis radicans) will soon be traveling along the fence. Keep in mind that this vine is rangy and once established it will definitely cover your fence, it just needs a couple of years to get started.
It typically sends up new shoots from the base as well as growing at the tips, the plant sort of sprawl and scramble over things. The more vigorous plant may be becoming established better faster than the other for whatever reason, or the top gorwth may have been trimmed back more.
You can try to thin out some of the new shoots from the roots in order to direct energy to the longer tips, but in a year or two the vines will be rather large overall and long on their own. Those new shoots will grow quickly.
Trimming them back in early summer will remove blooming wood for this season because they bloom on new growth made this year. The best time to trim them is in late winter, when they can be cut back as hard as you need to get the shape you want or control their size.
Enjoy your vines!
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