Vinca (Vinca spp.) also called periwinkle or creeping myrtle, can save you plenty of time in a shady garden. The spreading ground cover forms a year-round mat of deep green or variegated foliage, accented by blue or purplish flowers in spring, blocking out weeds and barren soil in heavy shade where grass won't grow, or on slopes and banks that can be a chore to maintain otherwise. Pruning is optional when your plants look lush and are well-behaved, but when your vincas look sad and spindly, or threaten to take over the yard, it's time to break out some tools.
Cut your entire bed of vinca down to 4 inches tall in late winter to early spring. A string trimmer is practical for large plantings, while you can hack back a small patch of vinca with pruning shears. You don't need to worry about making cuts at certain points on the plant -- it will grow in quickly to hide the cuts -- though you can cut to just above leaf if you only have a few plants and your neat-freak sensibilities get the better of you.
Pull out runners that are spreading into areas where you don't want them to go and cut long vines back with the string trimmer or shears to neaten the edges of your planting beds. Vincas send out long runners that root wherever they touch bare ground.
Rake up and dispose of the clippings in the trash or the center of an active compost pile. The plant can be invasive and is often spread to open areas bordering yards and gardens when clippings are dumped, allowing the cuttings to root and spread.
Clip back and pull out rooting runners from your vinca beds again in midsummer or whenever you notice them.