It's not uncommon to purchase what gardeners and professionals alike call pot-bound plants. Some plants form lots of roots naturally, yet others just stayed in the pot too long before the sale. So what do you do at planting? Do you slash, cut, pull or fluff the roots apart?
You have to do something. Allowing the plant to remain pot bound means you are going to be unhappy. Most likely, the plant is going to make slow growth, and in a few years it might die. Once tight in that root ball, the roots are not going to grow out into the surrounding soil. The only way to help the plant begin growth into the soil is by loosening the root system. Often, you do have to damage roots to help them regrow.
Many types of plants are affected by pot-bound conditions -- even annuals, perennials and houseplants. At planting time, the root systems should be disturbed in some way. With trees and shrubs, the recommendation is to make shallow, slash-like cuts into the root ball in three or four areas down the side. I prefer to think you and I might be able to just pull the roots apart. It would be easy to pull the outer roots loose at least a little in the plant pictured above.
Perhaps preparing the root ball for planting is just as important as digging the hole properly and watering. After all, if the root ball is not ready to make proper growth, all the other preparations might be useless.
One other thing you might think of is selecting plants that are not pot bound at planting. It's not always possible but worth checking before you buy.
