Pruning Coniferous Ornamentals

Because coniferous ornamentals generally have a strong central leader, they usually do not need much training except where a particular shape or effect is desired.  However, diseased, damaged and dead limbs should be removed as necessary and pruning can be used to correct problems in size, shape and to remove branches conflicting with other plants or structures. Branches can be thinned to reduce wind resistance in high risk areas. Timing and technique vary according to plant type and growth habit. Pruning tools should be disinfected between each cut in order to prevent the spread of disease. Wound dressings, though often recommended, have not been proven to hasten healing or decrease decay. If a wound dressing is desired for aesthetic reasons, ensure that it is registered for use on trees.

For removal of entire branches, pruning cuts should be made just outside the branch collar (swollen area at the underside of the branch-stem union)  as opposed to the once recommended flush cut. Avoid leaving stubs  as these will only die back, attracting insects and pathogens. Moroever, it is difficult, if not impossible, for the tree to 'heal over' such stubs. When removing large branches, a three-cut procedure should be used. The first cut should be made on the branch underside approximately 45 cm from the trunk or parent branch  and should not penetrate more than half of the branch. The undercut is designed to minimize the breaking and tearing of the bark. The second cut is the removal cut. It should be initiated on the top of the branch approximately 2.5 cm beyond the undercut (away from the trunk). The branch will then break off at this point. The final cut removes the stub and should be made just outside the branch collar as describe above.

Pine

In the spring, pines produce new shoots initially referred to as "candles"  because of their resemblance of candles in a candelabrum. Each elongated pine shoot typically consists of a basal zone where pollen cones  may be borne, followed by a zone of needle bundles called fascicles and seed cones closer to the tip.  Pines produce vigorous buds only near the tips of shoots, typically a terminal bud flanked by one or more sub-terminal lateral buds. These buds typically develop into the candles for the next year. On the main-stem leader, these buds form whorls of branches. Further down the shoot a few small buds at the base of needle clusters form but these are not very vigorous and generally remain dormant. If the buds near the tip are removed by pruning current year shoots late in the season, there is limited potential for re-growth from the weak buds associated with fascicles. If no shoots or weak shoots develop, the result may be gaps in the canopy. However, when pine shoots are pruned or sheared during the active growing season, as the candles approach their full size, additional, usually vigorous buds develop (called adventitious buds) at the bases of fascicles near the cut ends. These buds have the potential to develop into shoots similar to those of normal shoots. Because of the large number of such buds that can develop and form shoots, shoot and foliage density may increase. Such pruning is used in the production of pines for Christmas trees to get a fuller and more symmetrical crown.

Vigorous shoots in pines can leave a large distance between whorls which can be unattractive. For very vigorous candle shoots, pruning also has the effect of reducing shoot length and can be used to reduce the distance between successive whorls and thus control plant size. It should be noted that conifers cannot usually be pruned too severely because they have few latent buds on old wood below the foliage zone, so pruning back into old wood with no foliage will usually result in death of the stub.

If, for any reason, the primary terminal shoot (leader) is damaged or removed (topping), a nearby lateral should be trained to form the new leader; otherwise poor form will result. The lateral can be fastened to a splint or stake to train the lateral upwards. Branches of the whorl from which the lateral was selected should be trimmed in order to encourage the growth of the replacement leader.

Spruce and Fir

Spruces and firs, unlike pines, produce distinctive buds at intervals along the shoots.  Normally, however, it is the buds near the tip that develop into new shoots, producing a whorl-like distribution of branches.  However, the lateral buds further down can also form shoots, especially upon the removal of the buds near the shoot tips. The optimal pruning time for spruces and firs depends on the intended end result. Increasing the density of the plant can be achieved by removing half of the newly expanded growth in early spring. If the primary intention is to reduce shoot length, prune back to a lower lateral bud in late winter or early spring while the plant is still dormant. Like the pines, a lateral should be trained upwards to replace a terminal leader that has been damaged or removed; otherwise, two or more laterals may become multiple leaders, resulting in poor form that is irreversible.  As in the case of pines, branches of the whorl from which the lateral was selected should be trimmed in order to encourage the growth of the replacement leader.


Cedar and Juniper

Cedars (referring to Arborvitae - genus Thuja) and Junipers do not form winter buds and branch and rebranch continuously when conditions are favourable, forming a network of growing points and resultant shoots. Thus, because they have so many growing points that can continue to grow, they will tolerate a certain amount of shearing or pinching to control shape, size and amount of branching. To reduce size of cedars and junipers, it is best to thin shoot complexes to their junction with other shoot complexes. Tip pruning can be used to increase density and also to reduce size of junipers. These plants are typically clipped in early spring and again in early summer. However, pruning is usually not necessary and may be avoided in order to preserve the natural form of the plant. The removal of branches to thin spreading plants should be done such that overhanging branches conceal the pruning wounds.

Photos:
topiary1
barkridge
branch_collar
pruning_stub
first_cut
second_cut 
final_cut
candles
pollen_cones
pine_growth whorl
spruce_growth
spruce_whorl
fir_whorl
topiary2
before_pruning
after_pruning
cedar growth shoot complex 1
cedar growth shoot complex 2