Answer: I think this particular trumpet vine is in the wrong place, or the soil isn't of the same quality as that for your royal trumpet vine. When plants are stressed by the heat it's usually because they haven't fully established, or because they cannot fully establish because of soil conditions. Fertilizing will encourage new growth and if your plant is puny, fertilizer will stress it even further - perhaps to the point of death. I'd nurse it along with ample water until the weather cools in October, then dig it up and make sure the soil is draining freely. Amend as necessary and replant, then prune it back. It should respond with healthy new growth. If not, it just isn't happy with the site (reflected heat perhaps?) and you may want to consider moving it to a spot that provides some protection from hot afternoon sun (and no reflected heat). Best wishes with your trumpet vine!
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