So you're wondering. "When is the best time to plant Thuja Green Giants". "How do I know when to plant?"
The best time to plant is in early spring, about 1-2 weeks after your last frost usually around mid april. This gives your Thuja Green Giants a head start on getting their roots settled for the summer.
Spring planting is recommended for the middle of april if you are in zones 5 or 6.
If you are in zones 7,8, or 9 you can plant from September to May of the following year!