I recently bought some plants in containers that are root bound. Loosen and remove some of the potting medium until root ends are pulled out of the mix and extended out into the soil when planted. Work soil around extended roots with your hands, packing with feet will tear roots. I have read conflicting things about preparing the soil for planting. Some sources say to add organic matter like peat moss, while others say it is better not to use soil amendments.
Most plants grow better in soils high in organic matter.
Amend a 3-4 foot wide area no deeper than the root ball. Organic matter improves soil drainage of excess water, while holding moisture for better growth. Large plants can be moved as long as a good fibrous root system is present. I bought some plants on sale this fall, but don't want to plant them until spring, as the location where they are going has a large number of spring bulbs. Plants can be held over winter outside in the shade with roots buried with soil or mulch.