Nursery Pruning/Training Winston Dunwell April 1,

Pruning is the selective removal of part of a plant's top growth, namely branches and shoots, or part of its bottom growth, the roots, so as to control subsequent plant growth and behavior.

If branches are removed, the hormones (auxins) and complex metabolites, made by leaves and buds, will not be as plentiful and this will reduce root growth.

If roots are removed, the flow of nutrients from the soil and the supply of hormones (cytokinin) and storage compounds from the roots will all be reduced. If these are not so readily available to buds on the shoot system their growth will be controlled.

Apical Dominance The apical bud usually grows with greater vigor and is larger than lateral or axillary buds occurring on the stem below. The apex exerts a controlling influence over the shoot, and suppresses the growth of lateral buds.

If the tip is removed the apical dominance is broken and one of the buds below the apex will begin to grow and become the new leader; this one establishes its own dominance over the other buds.

Shoot tip is removed Cytokinins, water and mineral salts continue to pass up from the roots. Hormone accumulates in the upper part of the severed shoot where it stimulates young cells (and adventitious buds). Most likely to respond are in the youngest bud, that which is nearest the tip. The cells begin to divide, produce auxin and establish their xylem connection to the main system. In due course they develop as the replacement leading shoot.

Training high clearance street trees

Hydraulic pruners open and close at the speed related to the pressure applied versus the pneumatic that snap closed when the lever is pressed.

Hydraulic system for pruning budded field trees

Pneumatic system for nursery pruning

Pneumatic pruners commonly used in large orchards

Common to shade tree nursery training – Hand pruners and masking tape for training leaders

Highly respected publication

Prune to: A bud A branch the main trunk Or the ground

English publication but common to nursery libraries

Much of the landscape pruning is due to poor plant selection or lack of proper training in the nursery.

Excurrent Growth Habit - strong central leader

Decurrent Growth Habit – weak central leader

One dominant leader structure with: Branch diameter no more than 1/2 to 2/3 trunk diameter. No large-diameter branches growing below the final canopy

Co-dominant leader with included bark = poor form and potential hazard. Cannot be fixed – destroy rather than invest.

Co-dominant Leader

Fall Pruning Honeylocust

Co-dominant Leaders in the landscape are rarely removed

Spring planted

1st year

Training central leader

Removing potential codominant leaders in nursery.

Result of failing to remove interior branches

Following ice storm

It will have to be removed at some time

2 nd year

Codominant subordination – prune to outside bud result

2 year maple pruning/training result

Interior removal of leaves and small branches personal preference.

Pruned 2 year old maple

Owner/manager mark that pruning work has been checked.

Willow Oak

Bradford pear and finely branched willow oak following the ice storm both removed other willow oaks able to be kept

Remove abnormal growth.

Staking

Wooden Stakes

Bamboo

Electric Conduit 10’

Whoops!

Fiberglass Poles

“Flexing” before staking

Pruning Shrubs

Hand pruning in a large nursery to train multi-trunk birches

Large tree pruning is like landscape pruning

On over 4 inch trunk caliper space branches so that branches are not less than 15-18” directly above or below another

Large street trees with 13 foot clearance for trucks

Landscape pruning

Cut at branch collar

Cut too close: inside branch collar

Unacceptable flush cut

Sometimes storm damage leaves no alternative

Hazardous dieback stump when cut is made without foliar support

Have a planting plan for replace old existing plants

The best way to avoid routine pruning maintenance is to place the right plant in the right place.

Winston Dunwell