Periwinkle can be useful as a useful ground cover and a weed killer, especially on an incline or hill to prevent erosion, but note that it can also be invasive in some zones so it may need to be controlled with regular trimming and growing. If you plant, just keep up with it. Don’t let it spread where you don’t want it. However, you mentioned the same bed as azalea bushes. We would raise a caution using periwinkle with azaleas or other perennials and ornamental shrubs or trees in because it could spread and suppress their growth as well. Perhaps consider hostas or ferns for a nice green contrast that reduces the legginess of azalea shrubs. We also like sedum, especially Autumn Joy. Periwinkle may compete with the azaleas and could stunt them and move on to take over the rest of the garden bed!
Periwinkle can be useful as a useful ground cover and a weed killer, especially on an incline or hill to prevent erosion, but note that it can also be invasive in some zones so it may need to be controlled with regular trimming and growing. If you plant, just keep up with it. Don’t let it spread where you don’t want it. However, you mentioned the same bed as azalea bushes. We would raise a caution using periwinkle with azaleas or other perennials and ornamental shrubs or trees in because it could spread and suppress their growth as well. Perhaps consider hostas or ferns for a nice green contrast that reduces the legginess of azalea shrubs. We also like sedum, especially Autumn Joy. Periwinkle may compete with the azaleas and could stunt them and move on to take over the rest of the garden bed!