By Mike Allen
Written for the Winnipeg Free Press ‘Tree Care’ Column February 13, 2005
Pruning a branch is like carving a turkey. It can be done properly and effortlessly, or it can be butchered and end up looking like a mess. In Manitoba there are two main groups of above ground woody plants: DECIDUOUS or those that lose their leaves each fall, and CONIFEROUS EVERGREEN or those that keep their leaves or needles for a number of years.
Deciduous trees and shrubs are pruned differently from coniferous evergreen trees and shrubs. The differences are outlined below.
PRUNING DECIDUOUS WOODY PLANTS
The live twig and branch growth of newly planted trees should not be pruned for at least 5 years. The top growth is important to establish a strong root system. Well established young trees should be trained by pruning to improve their form if it is necessary, and to eventually control the height and extent of branches (where appropriate) as they mature. It is important to remove rubbing and broken branches, and any branches or multiple stems that are too crowded. This need especially applies to varieties of ash such as Manchurian and black ash, to varieties of linden, and to Amur and Schubert choke cherries. These trees can often come from the tree nursery with stems growing too close together. The weaker one or ones should be removed. Ideally all these trees should have one main central stem. Well spaced multiple stems can make an attractive specimen as well.
The best time to prune most deciduous trees and shrubs is in the dormant season especially from September to mid December, and from February to early April. Never prune birch and maple trees in the latter part of winter as they will “bleed” sap as the trees warm up in early spring. This creates an unsightly appearance, as the sap will become infected with moulds.
In Manitoba it is illegal to prune American elm between April 1st and July 31st inclusive; and Siberian (Chinese) and Japanese elms between April 1st and June 30th inclusive. Pruning elms during these periods makes them attractive to the native elm bark beetles. These beetles are mainly responsible for spreading Dutch elm disease as they feed on elm twigs.
If these trees are planted under overhead power and cable lines, consider transplanting them if it was done not too long ago; otherwise, the stem growth of most deciduous trees will interfere with the wires as they get taller.
Never top a tree with indiscriminate cuts. Always prune at a branch junction as shown in the diagram. The branch bark ridge just above the attachment of the branch must be preserved. The cut must include the branch collar. It is in this area where the tree will naturally grow wound sealing wood. Do not use tree pruning paint to cover the cut. The paint does not do much good. I do recommend that very large exposures of wood from cutting or from damage be treated with a clear wood preservative. Keep the preservative away from the edge of the cut or damaged area.
Pruning diseased portions of trees and shrubs will become necessary if they get infected. Proper and early pruning is the only way of controlling these diseases: black knot in Schubert choke cherry and May Day tree; fire blight in apple, pear, crab apple, mountain ash, cotoneaster, and hawthorn; early canker (bark-wood splitting) diseases of fruit trees, Russian olive, maple and Siberian elm; and, various gall diseases in poplar and willow. It is best to prune diseased plants during the dormant season. If pruned during the growing season, it is important to sterilize the pruning tool with diluted bleach after each cut so as to avoid passing the disease spores to a healthy part of the tree.
Never prune more than one-quarter to one-third of the living twigs and branches on deciduous trees. Older woody shrubs such as lilac, mock orange, honeysuckle and spirea can usually be renewed by removing all the older, decadent stems plus all the weak and crowded sucker shoots at the base of the plant. Pruning roses is an art, and how it is done depends on the type of rose plant. Check out books on rose pruning.
The proper pruning of fruit trees requires more specific techniques than I can add here. Fruit trees are dealt with in my pruning courses. (See attached list.)
PRUNING CONIFEROUS EVERGREEN WOODY PLANTS
There are two main groups of coniferous evergreens: (1) those with orderly arrangement of whorled twigs and branches such pine, spruce and fir, and (2) those with random arrangement of twigs and branches such as cedar and juniper. Larch or tamarack is a coniferous tree that loses its needles every fall. It has an orderly arrangement of whorled branches.
Living whorled branched evergreens rarely need pruning except to control their spread. The new tufts of emerging needles and twigs (often called “candles”) in the spring can be pinched off or cut off. Older growth can be pruned to a junction point where two (usually) side twigs or branches meet the main twig or branch. Never top these trees as they will produce multiple leader shoots that will require constant pruning each year. Young spruce and mugho pines can be shaped for ornamental purposes.
Random branched coniferous evergreens can be sheared except tall wide spreading cedars. These trees can be very open, and care must be taken to ensure that pruning does not leave a large empty place in the evergreen. If too much living green growth is removed, the evergreen may not be able to grow sufficient twigs and leaves to cover the gaping hole.
Never prune more than one-quarter of the living growth of any coniferous evergreen. This is especially true of ornamental cedars.
The best time to prune the living portions of all coniferous evergreens trees and shrubs is in the spring after the buds have opened. This timing will give cut areas a chance over the summer to prepare themselves for the winter season.
Dead coniferous branches are usually diseased. It is best to prune them during the dormant season. If pruned during the growing season, it is important to sterilize the pruning tool after each cut with diluted bleach so as to avoid passing the disease spores to a healthy part of the tree. Even living branches may have diseases that can be spread by improper pruning techniques. In preparation for the spring treatment of coniferous evergreen problems, it is best to have them assessed during the winter.