Answer: Trumpet vine or Campsis radicans is indeed a large vine, many people may not realize that when they plant it. If you need to prune it back to try to control the overall size, the time to do that is in late winter. At that time you can cut it back very hard, even as short as four feet, then allow it to regrow during the season. During the season you can try to direct or train the new growth in a direction you want it. This vine blooms on the new growth, so trimming it off in the summer will prevent or limit it from flowering. The plant spreads mostly by seeds, so picking off and/or raking up the fallen seedpods can be helpful in limiting the spread. Some gardeners will also trim it back in very late fall to try to remove seedpods before they fall off the vine. If there are seedlings coming up, you can pull them when they are small, it is easier when the soil is moist after a rainy spell. Or, you can try cutting them off repeatedly. This exhausts the root reserves eventually. Or, you can try cutting it off at ground level and putting a layer of cardboard over it, top that with a thick layer of mulch. This approach is intended to exclude light and smother it. You can also try applying an herbicide containing glyphosate, however be very careful to read and follow the application instructions as this a non-selective herbicide. Good luck with your neighbor's vine.
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