Vinca vines are also known by the names of Creeping Myrtle, Periwinkle, and Vinca minor. These vines will grow about six inches high and will send out vines about 18 inches long that will root and continue spreading, slowly forming a thick ground cover. They are identified by their evergreen leaves and striking purple-blue flowers. There are a few requirements the plant has that if met will keep it green and covered in the pretty blossoms.
Vinca vines can slow down in their growth if they have been growing in one spot for several years, forming a thick mat of stems and roots. Thin out the mass by pulling out about two thirds of the plants. Don't worry about taking too much since the amount of roots left underground will quickly sprout new growth which will inevitably also bring fresh blooms. Some growers actually mow the whole patch in the spring every year with a lawn mower at the highest setting to clean and invigorate the plants.
Check the moisture level of the soil under the vinca vines. Many time, homeowners over-water the vines in their efforts to stimulate plant growth and don't realize that after initial planting, vinca vines do not need to be watered. The soil should be allowed to dry out between rain showers to keep the plant from being stressed and not producing blooms. The extensive root systems will hold enough water to see the plant through almost drought conditions.
Fertilize the soil if the area has been covered in the same plants for several years. This is especially effective if you do it in conjunction with thinning out the plants (Step 1). A balanced fertilizer mixture of 10:10:10 ratio applied first thing in the spring should be enough for the year and will provide the nutrients needed for blossoming. The plants like a pH between 5.5 and 7.5, which is usually found when there is enough organic matter in the soil, so you can also apply a layer of compost to the patch.
Make sure the plant is getting some sunlight. The vinca vine grows wonderfully as a groundcover under the bases of trees, but still needs some sunlight to get through to it for part of the day to produce flowers. Thin out or cut back some of the overhead branches to allow some light to get through to your vinca plants.