Hello Peggy,

Both the fall and spring are good times for transplanting trees and shrubs. I tend to prefer to plant evergreens (including boxwoods) in the spring so that they do not lose water from cold winter winds, which can cause desiccation. This desiccation is most problematic when evergreens do not have established root systems, or if established evergreens are going into the winter already water stressed. 

Because of this, I would wait to buy boxwoods until the early spring and plant them at that time. If you feel like you really need to plant boxwoods this fall, I would plant them in early October and heavily water them in to make sure they aren't stressed by the dry soils. 

Good luck!

Robby