Once established, vinca ground cover plants will rage out of control if you don't routinely keep them pruned. Yet many gardeners avoid pruning these blooming plants for fear of inadvertently injuring or damaging them with incorrect technique. This is one plant that you don't have to be afraid of pruning. In fact, many enthusiasts of the periwinkle consider the fact that it's nearly impossible to kill to be one of its most desirable traits. So don't be shy, just get out there and give it your best. If the results are somewhat less attractive than you had envisioned, don't worry about it. Your vinca will rally nicely and return to its former glory quickly, none the worse for wear.
Mow large areas of your vinca ground cover down to 4 to 6 inches tall early in the spring after all danger of frost has passed for your area. It's best to do this before new growth begins to emerge. Cutting back hard like this will help to control the rampant growth habit of these plants.
Use a weed eater or shears to cut back smaller areas of periwinkles.
Shear your vinca back to 4 to 6 inches once more in mid to late April.
Cut out any dead, damaged or diseased stems as you notice them until fall.
Snip stray or unattractive stems back as needed to keep periwinkles looking presentable throughout the growing season.