Your post got me thinking - here is an excerpt from a website I found about buxus...

TRANSPLANTING

Boxwoods can be transplanted at any time except when they are in active growth or when the ground is frozen.

Rootballs should be large and solid. Dwarf boxwoods require a rootball with a
diameter at least half the diameter of the top of the plant. Tree boxwoods
should have a rootball with a diameter at least one-third the height of the
top.

Plants 2 to 3 feet higher broad should be shaded for a year after
transplanting. A lattice that cuts off about half the light should be used.
Shading is especially important if the plants are moved from a partly shaded
to an exposed site. The lattice should clear the foliage by 10 to 18 inches
and should protect at least the sunny sides as well as the top of the plant.

Newly transplanted boxwoods must be watered thoroughly and regularly. Direct a slow flow of water underneath the crow to the trunk. Continue watering until the rootball is wet all the way through. Build a low ridge of soil around the rootball to prevent wasting water and to allow thorough wetting.