Hi Robin, Probably the best known example of sun tracking (phototropism) in plants is Helianthus spp. Here I have also seen it in A. belladonna. However, if you are a cactus and planted during the sunniest, warmest time of year here, you would experience enormous sunburn damage. In the better nurseries, cacti are almost always marked on their south side. Pamela Pamela Slate P.O. Box 5316 Carefree AZ 85377