Answer: Vinca minor prefers full shade. It needs 2-3 slow, deep waterings per month, as well as several fertilizings annually. It doesn't like hot, dry conditions that we tend to get in the West during the summer. It likes rich soil full of humus that will hold moisture and yet drain well. I don't recommend fertilizing now, it might burn the plant roots; hold off until temperatures cool. You could spread compost around the plants to provide some nutrients and a layer of mulch to keep the soil cooler and to retain moisture. When you do fertilize, use a slow-release fertilizer.
Vinca major, which is a very similar plant, can take the sun somewhat better, but requires consistent moisture also. I hope this information helps.
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