Horticulture Principles and Practices

FIGURE 19–25
conifers.
Pruning
Remove top
of candle
of these branches may be necessary to provide for clearance under the tree. Conifers are
best pruned in spring or early summer, when most (e.g., pine, cypress, cedar, and spruce)
experience rapid growth. Some new growths (candles) may be removed or cut in half.
Pruning Christmas Trees
Christmas trees are characterized by a conical shape. To attain this desirable shape, growers
maintain a schedule of shearing to produce plants that are symmetrical and of uniform
canopy and density and with uniform spacing between branches. Shearing of
Christmas trees may begin in the third or fourth growing season, depending on the
species. It is important to shear pines in their active growing periods or no new buds will
form near cuts and dieback may occur. In the case of species such as fir and spruce, shearing
causes shoot growth to cease while buds form. These species may be sheared after
new growth begins. Pines tend to lose their shape readily (they grow less tight) and hence
require more frequent shearing than fir and spruce.
The density of the canopy depends on how the central leader is headed. The first
heading is done when the pine is about 12 inches (30.5 centimeters) tall. This lead shoot
is headed again in the next and subsequent seasons (up to four years) in the same manner.
If the lead shoot is cut short, the tree will be denser and more attractive but attain
harvest height after additional growing seasons. Whorls of branches develop in tiers as
the tree grows. Side shoots should be headed to about half the length of the lead shoot.
The sides are sheared to approximately 50 percent taper. To facilitate harvesting,
handling, and installation of the tree for display, up to about 12 inches (30.5 centimeters)
of the trunk from the ground is pruned to leave a clean base.
Pines characteristically have a conical or pyramidal shape. A significant difference
between pines and broadleaf trees is that pines mostly have one axis that does not branch
if cut back. Once a limb is removed, no replacement limb will be produced. When pruning,
no stubs should be left. The limb should be cut back to a visible live bud. Christmas
trees are sheared to obtain an attractive symmetrical and conical shape with uniformly
dense foliage (Figure 19–26). Pine, spruce, and fir produce circular growth of branches
(whorls) and branch once a year. To obtain a compact plant, the tips of the branches may
be pinched. Once formed, the internode between whorls is fixed and cannot be shortened.
19.17.2 PRUNING NONCONIFEROUS SHRUBS
Shrub problems in the landscape include the following:
1. Plant overgrowth. Shrubs may grow such that the canopy is too large. When this
occurs, the size of the plant may be reduced by carefully removing the long side
branches (thinning) or removing all large branches in the top of the shrub
(dehorning). Thinning should be done such that the shape of the plant is not
602 Chapter 19 Pruning