You may find that plants are in unsuitable positions in your garden for many reasons. Your ideas for your garden may have changed, you may be extending your house or you may simply have underestimated the size of a plant.
You can transplant many plants, though the size you can move will be limited by what you can lift. Note that soil is very heavy, especially when wet.
Large plants can be given a better chance of survival by root cutting earlier. Time may not permit this but where possible cut about 25% of the circumference of the root zone with a sharp spade and then the opposite 25%. You could dig a trench here about 30cm wide and 60cm deep and fill it with suitable organic compost to encourage vigorous new root growth.
Six months later cut the two other 25% sections of root zone and treat them in a similar fashion.
This technique allows the roots to become adapted to their changed circumstances and to develop fine new roots, giving your tree or shrub an improved chance of survival.
You'll have to plan ahead for this preparation. Sudden decisions preclude this treatment. Transplant your plant in the autumn or winter, as soon as the sun is cooler so that the tree or shrub is least stressed. Water the plant well a couple of days in advance of the move.
Dig a hole at the new planting site a little larger than the root ball you have cut. Dig it to the depth of your expected root ball.
Dig out your trenches around your plant, taking care not to damage the fine new fibrous roots that will have developed. Begin to dig beneath the base of your plant. Turning your spade over and then chipping away beneath the roots will assist in making the tree base come loose.
Cut any roots cleanly with secateurs and pull a hessian sheet beneath the tree by tilting it first one way and then the other while pulling the hessian through.
Tie the hessian around the root ball to keep its structure and carefully move the plant to the new planting site, ensuring the root ball is kept intact.
Lower the plant into its new location, leaving the hessian sheet in place. Backfill the planting hole in layers with a mix of natural soil and suitable organic compost. Lightly compact each layer and water it thoroughly, making sure that air pockets are excluded. Dish the final layer of soil around the base of the tree to provide a water reservoir and make sure that an area, of about one square metre is kept free of grass. Mulch heavily with Debco’s PotMate Mulch or Debco’s Green Wizard Mulch.
Avoid piling mulch against the trunk.
It's a good idea to weave a length of drainage pipe around the planting hole and up to the soil surface to act as an irrigation line. Pull the end of the pipe above the soil surface to prevent it becoming blocked with soil spillage.