Two years ago I planted vinca to replace a ratty looking grassy area of my garden, mostly in shade, and the vinca has done very well. There are some areas, though, where I will need to plant more vinca this spring to fill in some bare patches, and last summer the weeds got pretty thick in those spaces (clover, chickweed, etc.) I have been told to use Preen in early spring to keep the weeds down later. Is there anything else to use to prevent weeds in a bed of Vinca? Or anything that will kill the weeds but not hurt the Vinca?

Thanks, Joe