Answer: Periwinkle isn't particular about its soil requirements; in fact, it is known for its ability to grow almost anywhere. That said, it is happiest in soil that has average to rich fertility, is moist, humusy, and well enriched with organic matter. Once established it should not need fertilizing much if at all. Since your patch is suffering dieback, you might want to consult with your county extension office to make sure there is not an infection of some sort working its way through the planting. Also, if the area is very dry, it will take a long time for plants to take hold.
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