The spruces, firs and Douglas-fir produce a terminal stem (leader) and a major whorl of lateral limbs (top whorl) at the base of the leader each year. In addition, a number of buds develop along the leader between the top whorl and the terminal or end bud. Buds located along the stem between the whorls are called internodal or side buds.
The internodal buds develop into small limbs that contribute strongly to foliage and limb density the following season. The buds on the leader of the single-needle conifers are already pre- set and are clearly visible at the time of shearing. When the terminal bud cluster on one of these trees is sheared off, there is no increase in the number of buds and limbs such as occurs on the pines. Shearing spruces and firs only stimulates existing buds to grow into stronger limbs. These limbs help to cover open areas and give the tree a more uniformly dense appearance.
Time of shearing is not so critical with the singleneedle conifers as it is with the pines. The growing season for these trees varies depending on species, location in the state, topography, soil and weather conditions. Shoot growth normally occurs from about early to mid May until mid July to early August in Ohio. Results have been generally acceptable when spruces, firs and Douglas-firs are sheared from early August to the following March. The single-needle conifers can be sheared any time after height growth is completed, but trees sheared while the shoots are still growing may have additional stem elongation or the internodal buds may start to produce additional shoot growth. If this occurs, a second shearing may be needed to retain the desired tree appearance.
When leader growth exceeds 12 inches, normal shearing begins. In shearing the single-needle conifers, the leader or terminal shoot is cut back to the desired length, usually 10 to 14 inches, at a point about three-eighths to one-half inch above a single, large internodal (side) bud. This top bud usually develops into a single leader during the following growing season. After the leader is cut, the top whorl and the sides of the tree are sheared to the desired cone shape and taper. Cuts on the side of the tree can be made without regard to bud location on individual limbs. Existing buds develop into new limbs to increase density and uniformity of the tree.
Caution: When shearing leaders, cut back to a single internodal bud. If the cut is made just above two or more buds located around the leader at the same elevation, multiple leaders may develop. If a grower must use one bud of a cluster, the other buds should be snipped off or otherwise removed.