Figure 1. Interfascular buds developing at base of needle bundles on sheared Scotch pine.
Shearing is one of the most important cultural practices affecting production of high-quality Christmas trees. After an initial establishment period of two to four years, during which seedlings are developing an extensive root system, trees usually grow so rapidly that long internodes between whorls of limbs and laterals of varying length give trees an open, irregular appearance. Without shearing and shaping, a very small percentage of trees will be of salable quality.
The multi-needled pine species used for Christmas trees in Ohio usually do not have internodal buds between the major whorls of limbs on unsheared trees. Rather, there are dormant, fasicular buds located in the base of the individual needle bundles along the stem which generally do not develop unless the terminal buds on individual stems are removed (Figure 1). Research has shown that to obtain good results, trees of the pines should be sheared soon after shoot growth is completed, usually in early- to late-June in Ohio for Scotch pine (Pinus sylvestris), white pine (Pinus strobus), red pine (Pinus resinosa), and Austrian pine (Pinus nigra). When trees are sheared later in the summer and into the fall and winter, fewer buds develop at the base of needle fascicles on cut stems, and shoot growth and the number of effective whorl limbs that develop the following year become progressively less. White pine shoots sheared too late in the year may not form new buds and cut stems die back.
How trees are sheared is also very important. Even if they are sheared at the proper time, tree size and quality are affected by shearing techniques. The length to which the terminal shoot is cut is particularly important because the basic outline and taper of the tree is generally shaped to conform to the length of the leader. Obviously, terminals should be cut as long as possible so that marketable-sized trees can be grown in the shortest possible time; however, if shoots are too long, tree quality may be affected (Brown, 1960; Brown, 1964; Brown, 1981; Brown, 1984).
Figure 2. Internodal buds and limbs on West Virginia balsam (above) and Frazer fir (below) terminal shoots.
Unlike the pines, the “single-needled” conifer species — firs (Abies sp.), spruces (Picea sp.) and Douglas-fir (Pseudotsuga menziesii) — do not have fasicular buds at the base of needles but have internodal or “side” buds along the stems between major whorls of limbs, most of which are pre-set and clearly visible after shoot growth has been completed (Figure 2). Although most of those buds develop into internodal, lateral limbs, those limbs often remain relatively small on uncut stems, while on stems that have been cut, they grow into longer and stronger limbs that help to cover open areas and give trees a more uniform, dense appearance.
The quality of trees of the single-needled species can also be affected by the lengths to which terminal shoots are cut; however, effects of time of shearing are less well documented. In a study with Norway spruce (Picea abies), trees were sheared in July, October, January, and April in each of five years (Brown and Tryon, 1961). Tree quality was improved considerably as the number of annual shearings increased, but no pronounced differences were noted between times of pruning, except in one year when lateral limbs developed from internodal buds on cut stems of some of the trees sheared in July and an additional light shearing was needed to correct irregularities in tree shape. Although most Christmas tree growers currently shear single-needled conifers from fall through the following spring before new shoot growth begins, some shear in mid- to late-summer.
While Scotch pine and white pine continue to make up a high percentage of the Christmas trees planted and harvested in Ohio, that percentage has declined in recent years. Concurrently, planting and harvesting of trees of the single-needled conifers have been increasing.
From 1984 to 1996, the percentage of Fraser fir (Abies balsamea var. fraseri) planted more than doubled to approximately 12 percent of the total, and harvesting tripled, also to approximately 12 percent. In addition, trees of West Virginia balsam (Canaan) fir (Abies balsamea var. phanerolepis), which were introduced into Ohio plantings in the late 1980s, made up approximately 8 percent of the planting and approximately 5 percent of the harvest in 1996 (Brown, 1983a; Heiligmann and Passewitz, 1998).
The purposes of the research reported here were to study the effects of time of shearing and length of terminal shoots on the development and quality of West Virginia balsam and Fraser fir Christmas trees. In addition, the effects of annual applications of nitrogen fertilizer on tree development and quality were evaluated.