Answer: Clover is usually found in areas of low fertilty (especially low nitrogen). Fertilizing the vinca will help the vinca and it may also help reduce the population of clover, but will probably not eliminate it.
Using a weed killer will be diffiocult in this area because a broad leaf weed killer that would tke care of the clover will also kill your vinca (also a broad leaf plant). You would have to be careful and apply the weed killer only to the clover. If the clover and vinca are badly intertwined you might want to kill out the whole bed and start over.
Wish I had more solutions!
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