Thanks for your question Don. Arborvitae will perform best in full sun. Full sun means that it the sun should shine directly on the plant for at least 6 hours. More is even better. You can add up all the sun that it gets to get the total. For example it might get 2 hours in the morning and 5 more in the afternoon for a total of 7 hour of direct sun. You should make these estimations during the growing season in June or July for instance. How much sun it gets in early spring, late fall or winter when the plant is dormant has no relevance.