Answer: Yellowing leaves can be normal and natural if the leaves are the oldest and closest to the ground. If your vinca is putting out healthy new growth, it's just fine. If the new growth is yellowing, you may need to feed your vinca (you can use a foliar spray such as Miracle Gro since your plants are on a slope). When you water, be sure to start at the top of the slope and allow the water to run long enough to soak the top 6 inches of soil. That's where most of the roots are concentrated and where the water will do the most good. Best wishes with your vinca!
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