Where a variety of species and sizes is being grown, operational priorities should be established to obtain best results from shearing. Two basic principles related to shoot growth on sheared pines apply: 1) shearing pines as early as possible results in more time for the interfascicular buds to develop and mature. Large, healthy, mature buds produce shoots the following year that are sufficiently long to allow normal shearing and 2) after shearing, a minimum of 12 to 14 inches of leader growth is needed the following year if acceptable taper is to be maintained. In young plantations such as those only 2 to 3 feet in height, new leader growth just begins to exceed 12 inches. To have more than 12 inches the following year, young trees should be sheared first so the number of buds and vigorous limbs produced will be maximum, and growth the following year will allow for normal development. Because white pine is very sensitive to time of shearing, small white pine should be given top priority in the shearing schedule. Larger Scotch pine should probably be the last group of trees sheared during the summer.
Between the smallest white pine and the largest Scotch pine on the Christmas tree farm, shearing operations during the summer should proceed in accordance with the species and/or size classes of trees, starting with the younger, smaller trees and then progressing into the larger size classes. Red and Austrian pines are less affected by delayed summer shearing than white pine but more so than Scotch pine. Thus, smaller red and Austrian pine should be sheared before smaller Scotch pine.
Depending on location within the state, site factors and weather conditions, all shearing of white pine should be completed by early to mid July, red and Austrian pine by mid to late July and Scotch pine by late July to early August. However, shearing should not be delayed. Results are best when all pines are sheared just after completion of height growth.
Once the rush of the pine shearing season is over, shearing on the single-needle conifers can proceed at a more leisurely pace. Spruces, firs and Douglas-fir can be sheared with good results from late July or early August and continuing until just before new growth starts the following spring.
Examples of time required for shearing different size trees and using different types of equipment are presented in Table 8.