Periwinkle needs watering most when it is first planted, during droughts and in late fall before the ground freezes. Although it tolerates dry periods pretty well, during prolonged drought water generously with a drip irrigation system or sprinkler at least once a week.
For more information see file on Choosing Watering Equipment.
Periwinkles need only one feeding a year. In the spring sprinkle some fertilizer on the soil around the vines. Try not to get it on the foliage. Beware of overfeeding, which stimulates abundant foliage growth at the expense of the flowers.
For more information see file on Choosing Fertilizer.
Cover the soil in and around newly planted periwinkle sprigs with 2 to 4-inches of organic material such as compost chopped leaves or wood chips. This will help the soil hold moisture and discourage weeds. After a year or two, the vines will have filled in and no further mulching will be needed. Hand-pull any weeds that manage to penetrate this cover.
For more information see file on Using Mulch.
Pruning normally isn't required, but you may occasionally need to clip off new periwinkle sprigs that sprout from the spreading runners that grow beyond their allotted space. Pinching back runners will encourage the periwinkle to become bushier.
For more information see file on Choosing Pruning Tools.