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Pruning

Selecting the proper time to prune is important. Heavy pruning at the wrong time of year can stimulate unwanted growth or prevent flowering or fruiting. Before pruning, consider time of year, type of plant and flowering periods of certain plants. See the table below.


Time of Year to Prune Various Types of Plants.
Season
Type of plant Fall Winter Spring Summer Comments

Early Late Early Late Early Late Early Late
Deciduous shrubs







for shrubs
that flower before
June 1
Deciduous shrubs







for shrubs
that flower after
May 30
Deciduous
trees
a








Conifers –
Shrubs and
Trees








All conifers
except for pines
(see below)
a
Pines
a








Broadleaf
evergreen
shrubs








For shrubs grown
for flowers
Broad leaf
evergreen
shrubs








For shrubs grown for foliage (hedge)

When to Prune New Growth on Pines

Pines have buds only at the tip of the branches. If a branch is pruned after a growth flush and the terminal bud is removed, regrowth is impossible. Pine branches should be pruned or pinched in early summer when the new branch (candle) has begun to elongate but before the needle bundles open. This pruning causes the growth to be more compact but still allows buds to form for the following year.

1. Heading Cut – Cutting plant stems back to a bud, twig or stub. Potential problems – a stub is often left and may become infested with insects or diseases, vigorous growth may be stimulated, and the new growth may be weakly attached and could split or crack under pressure. This may also negatively affect the desirable, graceful arching habit of some shrubs.

Heading cut

2. Thinning Cut – The removal of a branch at its point of origin or cutting back a branch to a lateral branch about 1/3 the diameter of the branch being removed. Advantages – No stub is left, the plant retains its natural shape, and vigorous new shoot growth is avoided. Caution: removing more than about 30% of the foliage can stimulate new growth even if thinning cuts are used.

Thinning cut

Using thinning cuts on selected branches to improve light and air penetration to interior foliage

The size of the branch determines the location of the pruning cut. A small twig or branch can be pruned back to a bud or lateral branch. On a small branch make the cut one-quarter inch above the bud, and slant the cut away from the bud (see diagram).

Length of pruned stub

1. Natural target pruning is the technique used when cutting beyond the bark ridge and branch collar (collectively called the branch shoulder). see diagram below. This cut provides a physical barrier to disease and injury within the intact branch shoulder. This compartmentalization of the wound stops injury from spreading into the main trunk of the plant where it could spread throughout the plant and be damaging to the plant as a whole. The wound size is also smaller allowing callus to grow quickly over the wound and limits potential exposure to insect and disease infestation.

Natural target pruning

2. Large branches or limbs (those to heavy to hold while cutting) are removed by a series of three cuts. The first cut is made on the underside of the limb about 12 inches from the branch crotch and should go about one -quarter of the way through the limb. The second cut is made on the top side of the branch about 2 inches farther out on the limb from the undercut. Cut down until the branch cracks off. As you are completing the second cut, careful to watch for the branch suddenly dropping or moving quickly as the branch weight accelerates limb removal. The third cut is made on the top side of the stump left over, just outside of the bark ridge and branch collar. See the diagram (on next page) to determine where the final pruning cut should be made. Be sure to support the branch stump when making the final cut to avoid tearing the tissue when completing the cut.

Three cut method diagram for pruning large branches:

Three-cut method for pruning

Proper tools should be used to make a clean pruning cut and to minimize damaging plant tissue. If the plant tissue is crushed or torn it can leave the plant susceptible to disease and insect problems. In addition, more time will be needed by the plant to have tissues grow over the wound. Pruning tools should be the correct size for the job and be made of tempered steel that can hold a sharp edge. Making a pruning cut should be relatively easy when the correct size of tool is used. Hand pruners should be used to cut branches that are less than one-half inch in diameter. Lopping shears should be used for branches between one-half and 1 inch thick. A bow saw or pruning saw should be used to cut branches larger than 1 inch thick. Be sure to make a clean cut with the proper tool.

Sanitizing pruning tools

Pruning tools should be disinfected after each cut, under ideal circumstances, to avoid spreading diseases from plant to plant. At the very minimum disinfect pruning tools after finishing one plant but before beginning to prune the next plant. To sanitize tools, dip the cutting edge in a disinfectant solution such as denatured alcohol, methanol or diluted household bleach (1 part bleach plus 9 parts of water). An alternative is to spray the cutting blade with a disinfectant solution. When using bleach, make sure to apply a thin layer of oil to the blade before storing to avoid rusting of the tool.

Pruning paints and asphalt emulsions are not recommended for use on pruning cuts as they may actually seal in disease-causing organisms or promote rot.

University of Idaho Extension

Physical Address:
E. J. Iddings Agricultural Science Laboratory, Room 52
606 S Rayburn St.
Moscow, ID

Mailing Address:
University of Idaho Extension
875 Perimeter Drive MS 2338
Moscow, ID 83844-2338

Phone: 208-885-5883

Fax: 208-885-6654

Email: extension@uidaho.edu

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Barbara Petty