I have them in large containers and they do very well. They are planted in a soil less mix that drains well, fortified with about one third compost. I would not disturb the roots even if they were balled in clay. Remove the burlap only from the top of the ball, let the rest rot away. If you try to remove all the burlap you risk disturbing the root ball and killing the plant. If your mix is fast draining you should have no problems. Mine are protected from afternoon sun. Al

Daphnes like very sharp drainage and things somewhat on the dry side. I don't like the sound of that heavy clay, but I also think you're right to be concerned about root disturbance. If it were me, I would try to remove that clay, even at the risk of damaging some roots. I'd try removing the burlap and, holding the plant by the root collar, swishing around gently in a tub of water to loosen and remove as much clay as possible. Avoid letting the roots dry out or be exposed to too much sun. Next, your pot and potting mixture: I've found daphnes to root down when they can, so I'd choose at least a standard height pot and perhaps a long tom if you can find one. Clay for air exchange, if you don't mind the weight. For the medium, you can't go far wrong with one of tapla's mixtures posted in this forum: 1:1:1 fine bark chips:Turface:crushed granite. These ingredients aren't always the easiest to find, so my alternative for my D. odora is 2:1:1 peat moss-based potting soil:coarse sand:perlite.

I don't have a good feeling about using field grown daphne's for container growing. They can be such tempermental plants.

If you DO decide to amend a standard potting soil (which I strongly suggest that you do), don't use sand but something much larger. Granite grit (called chicken grit) is great, or aquarium gravel...something along that line. Turface MVP is terrific if you can find it.

Daphne odora is actually a great subject for container growing - it is one way you can assure the soil conditions it requires. DO NOT disturb the clay root ball - daphnes are extremely particular about root disturbance of any kind and that is often what causes problems with new plantings and is the primary source of transplant failure. Just make sure the root ball is well hydrated before planting and don't allow the container to dry out excessively - keep just barely moist at all times.

FWIW, we pot up all our B&B daphnes at the nursery for long term storage/handling during the season.