February pruning workshop at the Demonstration Gardens 

By Drexie Malone, Lead Gardener

Christina Pfeiffer brought eleven students from her Edmonds College Horticulture class for a four-hour pruning workshop on February 20, 2024.

Christina was provided a list of priorities, and together we determined what pruning was needed based on previous maintenance, the health of the plant, goals of pruning, and time available. 

These trees and shrubs were pruned (or not) for these reasons

Parking island trees

The branches of the two Callitropsis nootkatensis (Yellow Cedar) were limbed up, or arborized, to meet the eight-foot height requirements of the path and to lessen the dense growth, allowing a sight line through the island and more light for understory.

Cedars before
Cedars after

The instructor declined to prune the lower branches of the Acer glabrum (Rocky mountain maple) competing with the branches of the Acer circinatum (Vine maple), given the evidence of scarring and stress.

Visitors Center gardens

In the concrete retaining wall bed on the east side of the building, the Lonicera fragrantissima (Winter honeysuckle) was pruned to de-tangle branches and limit the height and width of this large shrub.

The Mahonia aquifolium (Tall Oregon grape) was leaning towards the Visitors Center awning. The students pruned out the tallest and oldest stems and reduced the size of the shrub and its encroachment. Visitors can now see the bulletin board on the side of the building from the entrance, and the pathway feels less like a tunnel.

Mahonia before
Mahonia after

At the entrance to the Gardens in the bed with a split rail fence, another Mahonia aquifolium was very large—tall and wide. The class removed stems to limit the height and to a lesser extent the width, to allow a view into the Gardens from the entrance ramp.

Ethnobotany Garden

The ancient Corylus cornuta (Hazelnut) may be the largest in the Gardens. Its old branches grow horizontally, blocking the sun and space from other plants. The good news is there are many young, strong vertical branches emerging. The class wasn’t able to prune through the large stem bases with hand saws, so they trimmed up other partial cuts made a year ago, allowing the tree to look “untouched” and a small amount of light gained toward the north.

The Symphoricarpos albus (Snowberry) growing around the Hazelnut tree tends to spread into the path, with shoots emerging in all directions. The class dug out the roots of the small stems and cut the larger stems at the base.

A Vaccinium ovatum (Evergreen huckleberry) grew here, with many siblings, too tall to see into the garden; the class brought the height down.

North Garden

The Spiraea stevenii (Steven’s Spiraea) represents a group of shrubs that is difficult to prune because of its many small branches. For that reason it’s common to see them sheared in landscapes. Repeated shearing shortens the lifespan of the plant.

Since the goal is to support the plant as long as we can, the class used a rejuvenative technique by taking out large, horizontal-growing or tallest stems to minimize the spread of these shrubs and encourage new growth from the base. After the shrub flowers, it can be deadheaded to further shape the shrub and allow for a second bloom.

Spirea before
Sprirea after