Answer: Can you think of any ways in which the two plants have been treated differently? I'm wondering why one would be affected, but not the other. Is one in brighter sunlight? Gets more water? Different fertilizer? Here are some growing tips:
Confederate jasmine (Trachelospermum jasminoides) are not too fussy about soils, preferring slightly acid soil containing a fair amount of organic matter. The soil should not be excessively dry. They prefer a little shade from bright, hot sun.
It sounds like the roots of the ailing plant may have been damaged somehow. Are these new plants? Did they both get adequate watering last summer? Could one have gotten an "overdose" of concentrated fertilizer? Sometimes one plant will be weaker than another for some reason, and will react more strongly to lack of water, especially in their first season. Also, pests generally attact weaker plants first. Common pests of the plant include spider mites (tiny spider-like creatures--look for very fine webbing on new growth), mealybugs (look for cottony white spots, especially in leaf joints), and scale insects (look for non-moving, oval raised bumps, often on leaf veins and a sticky substance). Inspect the plant carefully for signs of these insects.
Other than that, I can't think of any reason for one plant to be ailing, while the one right next to it is fine. I would take a cutting of a damaged branch, sealed in a plastic bag, to a local nursery. They may be able to help further.
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