Plants on sale have either been grown in a field or in a container.

Some plants, such as roses, which are grown in the ground and then dug up for sale, are referred to as bare-rooted. They can only be dug up once the leaves have fallen - so if you want to be sure of getting what you want, you have to order them in advance, then wait until winter for delivery. You should be careful to protect these bare roots from drying conditions of wind, sun or heat - keep them well wrapped - and plant them while still in the dormant stage

Evergreens that are field grown are dug up and root-balled (ie the root system and soil are wrapped up in hessian sacking) protect the whole plant from drying conditions because the roots cannot replace lost moisture. The sacking need not be removed at planting because the roots can penetrate it and it will rot eventually, but you should cut through/undo the knots around the trunk. Pot-grown evergreens are also available.

Containerised plants are more expensive than bare-rooted plants but more convenient because they can be planted all year round (except when the ground is waterlogged or frozen).