Periwinkle is the common name used for two plants in the genus Vinca: bigleaf or greater periwinkle (Vinca major) and common or lesser periwinkle (Vinca minor). These plants are often used as a perennial groundcover in U.S. Department of Agriculture plant hardiness zones 4 through 11, depending on the cultivar. As happens with other low-growing groundcovers, weeds can infest periwinkle, especially before establishment. Removing weeds prior to planting is ideal, but once periwinkle is planted, you can remove, kill and control weeds using one or more control methods.
Moisten the soil in the periwinkle bed with 1/2 to 1 inch of water and wait 30 or more minutes for it to become thoroughly moistened; removing weeds is easiest when the soil is moist. Grab the weeds at their bases and remove their entire root systems. Gather and discard the weeds for trash removal. Perform this task regularly as needed, before the weeds set seed.
Apply 2 inches of mulch, such as peat moss or wood chips, around and between the periwinkles. Replenish this layer of mulch as it decomposes to maintain a depth of 2 inches. Mulch blocks sunlight to prevent weed seeds from germinating, and can control up to 90 percent of weed problems, according to Purdue University.
Spot-treat persistent, actively growing weeds with a ready-to-use selective herbicide designed to kill the problem weeds, but that is safe for periwinkle. One that contains fluazifop-p-butyl, for example, kills grassy weeds and is safe for common periwinkle. Spray the herbicide directly on the foliage until it is wet. Perform this task on a dry day so the herbicide is not washed away before the weeds absorb it.