The standard for the size of the rootball of seedlings offered by nurseries in the United States is set by the American Nursery and Landscape Association. This standard, which varies in line with the type of tree and species, is supposed to insure that the plant will be able to hold out against the stress of being transplanted.
Measuring Tree Size
The American Nursery and Landscape Association utilizes the phrase “caliper” for the thickness or diameter of a tree. The permitted size of the root ball is based on the caliper of a nursery seedling. For citrus trees, the caliper is measured 1/2 inch above the bud union, where the scion is grafted onto the main stock. On a citrus tree, the bud union should be at least 6 inches in the ground. The minimal caliper for citrus trees is 3/8 inch. Lime, mandarin and tangerine trees might be offered with 5/16-inch caliper.
Minimum Rootball Width
A citrus tree with a caliper of 1/4 inch to 5/16 inch needs to have a root ball at least 8 inches wide. A tree with a caliper of 3/8 to 5/8 inch needs to have a root ball at least 10 inches wide. A tree with a caliper of 3/4 inch or above should have a root ball at least 12 inches wide.
Minimum Rootball Depth
If the width of the ball is less than 20 inches, then its thickness should be less than 65 percent of its diameter. If the width of the ball is greater than 20 inches, then its thickness should be less than 60 percent of its diameter.
Planting the Rootball
A citrus tree ought to be planted in the spring after the danger of frost has passed and at place where it will get whole sun for most of the day. Citrus trees such as well-drained sandy loam or loam soil. To learn if the soil drains properly, dig a hole 1 foot deep and fill it with water. If the hole has not drained by the next day, plant the tree at a different place. Dig a hole as deep as the root ball and twice its diameter. Do not place fertilizer in the hole; that can hurt citrus roots. Wash off about 1 inch of soil from around the root ball so that the roots make contact with the surrounding soil and, being careful not to break the roots, put the root ball to the hole and fill it with soil. Following a light tamping, the cap of the root ball must be 1 inch above the ground. Create a circular ridge of soil about 6 inches high just beyond the main ball to form a basin and water the tree several times to settle the soil around the roots.