Experts and BHG readers answer.
Star Jasmine is yellow
Yellowing foliage can be a symptom of various problems. Both over- and underwatering may produce yellowing leaves. If you are watering with a soaker hose, though, I'd suspect that the plants are not being overwatered unless there is a leak in the hose that's keeping the soil saturated. Is the soil quite moist or extremely dry? That would be a good clue, too..
Yellowing could be caused by a nutrient deficiency. What is the pattern of yellowing? Is it only the older leaves that turn yellow? That could signify a nitrogen deficiency. Are the leaf veins still green? That could indicate a micronutrient deficiency such as iron. It could also indicate a soil pH that's too high, which would induce the iron deficiency.
Yet another possibility is yellowing of leaves from insect feeding. Examine plants closely for the presence of insects or mites, and treat accordingly.