1:Do not let the roots dry out.
Try not to cut off the fine root hairs.
Replant at the same depth.
Cut back drastically, say by at least half in height. This is because you are bound to loose many roots and it keeps the balance between roots and top correct.
Keep well watered for at least 6 months.
2:Ideally do as you say with the trenches and loosen the hedge/ plants so no roots are holding into the soil, then back fill, firm and leave for 12 months. This is in effect wrenching the roots as tree nurserymen do to avoid tap roots and establish a system of fine root hairs. In forestry this is done to young transplants which are then sold as 1u1 transplants, that is one year seedlings unercut and grown on for another year. This gives a really good root system. With larger trees or shrubs it is done for the same reason but also often so a rootballed tree or shrub is grown suitable for replanting with a good fibrous rootball.
3: Take cuttings, you only need to stick them in the ground and they usually grow. This will be your fall back plan if all else fails. :)
PS I have some experience of this. :)
Ivor
