Horticulturists generally agree that the ideal specimen for planting has sufficient roots to fill the soil ball (either pot-grown or a ground-grown, balled and burlapped plant), but not so much root that there is obvious crowing or congestion. The best plants are vigorous both above and below the ground.

For pot-grown plants, slip the pot off the root ball. If roots are crowded and matt-like, they have probably been in the pot a long time and have used up whatever nutrition was original in the soil. Such roots may be difficult to establish in new soil unless they are teased apart before planting.

Once loosened, this allows them to grow into the surrounding soil, away from the main root mass and toward better soil conditions. Many rhododendrons can tolerate the landscaper's trick of slicing the root-ball vertically before planting.

Plants that don't have many roots visible at the soil-pot interface are either newly potted (i.e., recently transplanted) or suffering from moisture, nutrition, disease or insect damage. In the first instances, as you are relieving the grower of the significant cost of growing the plant to a reasonable size its not uncommon to ask for a price reduction. Howver, if the cause is any of the later ones, it is wise to not purchase the plant.