Birds cause deformed leaders by perching on them as they expand in the spring. Weather and climate also have impacts including damage from too little or too much precipitation, winds, ice and snow. Newly planted trees may require staking to correct leaning trees and to correct multiple leaders during their first three years. In June and July, starting two to four years after planting, each tree is sheared to control growth, shape, density and form. Growers may thin the number of shoots in each tree and control the expansion of the leader to produce trees that have desirable density of leaves and branches.
Terminal growth is limited to develop trees with greater density and symmetry.
Trees are shaped with either shearing knives or mechanical shears or trimmers to produce that ideal shape for a Christmas tree, which is twice as high as wide. Growers also may basal prune each tree, allowing for easier harvesting and providing a branch-free handle for the consumer. Some species of trees produced in Iowa require an application of a tint and anti-desiccant to maintain their good green color during the Christmas season. These dyes are normally applied with mist blowers or hand sprayers during September to November. Starting in October, growers get ready to market their product.