Ohio Christmas Tree Producers Manual

Bulletin 670

The Pines

Pines normally produce whorls of lateral branches with no internodal buds along the stem. Unless there is genetic variability in the species or unusual weather conditions occur, most pines grown for Christmas trees in Ohio commence growth in the spring, experience a single shoot growth period and then set buds. Normal bud set on an unsheared leader of Scotch pine consists of a terminal bud, upper lateral buds, lower lateral buds and interfascicular buds. Interfascicular buds are sometimes called dormant buds and are very small, tiny buds that occur between and at the base of the needles (Fig. 40). Their growth and development are normally controlled and suppressed by the terminal and lateral buds on an unsheared leader. Development of a sufficient number of healthy, vigorous interfascicular buds is the key to quality pine Christmas trees. When the terminal cluster is sheared off, the restraining effect on the development of the dormant buds is destroyed, and a number of the dormant buds located just below the cut will develop into shoot buds (Fig. 41). The number and vigor of buds that form depends on the time of year when shearing is done. The best possible time to shear the pines is just after height growth has been completed and before stem or branch tissue has hardened off and turned woody. At this time, the numbers of large, vigorous buds that develop below the shearing cut will be from two to four times greater than the numbers on uncut stems. Shoot growth from these buds the following year will be almost as much as that on unsheared trees. Additional limbs that arise from dormant buds add greatly to foliage density (Figs. 5 and 6).

Fig. 41: New buds forming at base of needle bundles on a sheared Scotch pine terminal.	Fig. 42: Limb development and shoot growth the year after shearing on Scotch pine terminal sheared in mid June.

In Ohio, the most appropriate time to shear the pines is from early to late June. Time of shearing varies with location in the state and other factors affecting tree growth. The shearing season usually begins 10 to 14 days earlier in the southern than in the northern half of the state. There are two key points to remember: 1) pines are sheared during the growing season and 2) best results are obtained when trees are sheared just after completion of height growth. As trees are sheared progressively later in the summer, dormant buds have less and less time to mature and develop into strong, vigorous buds. Fewer buds develop, and growth the following season is reduced. A tree sheared in late summer produces only a few weak buds. Growth and foliage density may even be less than that on an unpruned tree (see Figs. 42, 43 and 44). Poor results from late shearing vary somewhat for the different pines. Scotch pine is least affected, while white pine is most drastically affected. It is important that growers shear white pine as early as possible. Limbs of white pine sheared in mid to late summer will often die back (see Fig. 45).

Fig. 43: Limb development and shoot growth the year after shearing on Scotch pine terminal sheared in mid July.	Fig. 44: Limb development and shoot growth the year after shearing on Scotch pine terminal sheared in mid August.	Fig. 45: Die-back of white pine terminal sheared during the winter.

In shearing the pines, the leader or terminal shoot should be cut to the maximum length possible while still maintaining proper density and taper of the trees. Although leaders are usually cut to 12 inches, growth is variable. The usual range in sheared leaders is 10 to 14 inches. Shearing to shorter lengths can add one or more years to the length of time needed to grow a marketable tree. The cut on the leader should be made at a 45 degree angle to the stem's upright or vertical axis. The simple procedure of cutting the leader at this angle puts one needle bundle (fascicle) at a higher position on the stem and minimizes the problem of multiple leaders (Fig. 46). If the cut is made straight across the stem at a 90 degree angle, two or more needle bundles may be equally close to the upper edge of the cut stem, and multiple leaders often develop (Fig. 47).

Fig. 46: Sloping cut on terminal of Scotch pine. One needle bundle is left near the apex of the stem. This favors development of a single new terminal after shearing.	Fig. 47: Flat cut on Scotch pine terminal. Several needle bundles are left at the same height near the cut edge, favoring the development of multiple leaders after shearing.

After the cut is made on the leader, limbs in the uppermost or top whorl should be cut 3 to 5 inches shorter than the leader. One guideline is that the top whorl length should be about two-thirds the leader length-if the leader length is 12 inches, the top whorl of laterals should be about 8 inches. In shearing operations, the leader and top whorl are the key parts of the tree and are extremely important in building the basic branch framework of a quality tree (Fig. 40).

Once the leader and top whorl have been sheared, proceed to shear around and down to achieve the desired shape. One way to side shear is to draw an imaginary line from the top of the leader (after it has been cut) to the outer limits of the basal whorl. Then cut off any branch that projects outside the imaginary line of the desired cone shape. Angle of cut on the side branches is not important, but if hedge shears are used, cuts should be parallel to the plane of the cone and not cut horizontally towards the stem of the tree (Fig. 48).

Fig. 48: When shearing with hedge clippers, blades should be kept parallel (L.) to the plane of the tree rather than perpendicular (R.) to the plane.

Basically, shearing pines is a matter of timing. Trees should be sheared at or soon after completion of height growth, if possible. Through shearing, the grower limits height and width to create the desired appearance.