Colorado Multi-Site Woody Plant Trials

Colorado Multi-Site Woody Plant Trials

Dr. James Klett, Eric Hammond, Jane Rozum and Rob McDonald

Colorado State University, Department of Horticulture and Landscape Architecture

and Adams County Extension

Manzano Bigtooth Maple (Acer grandidentatum 'Manzano') Planted in 2013

Colorado can be a tough place to be a plant.  Options for woody plants and particularly tree selection are limited in much of the state due to climate, soils, and disease and insect issues.  Late and early frosts, dry winters with fluctuating temperatures, and calcareous alkaline soils have traditionally limited the diversity of species which can successfully be grown in many parts of the state.  Increasingly limited and expensive water resources coupled with a dry climate also make many mesic species less desirable.  At the same time, many commonly planted species have been affected by serious disease or insect issues such as Dutch elm disease, thousand cankers disease and emerald ash borer.

   

Pests such as emerald ash borer
 are one limiting factor in species selection

In response to this, Colorado State University (CSU) began a multi-site woody plant evaluation program to trial underused and “new” woody plants with the goal of enlarging the size of the plant palate available in the state.  The trial was started in 2002 at five different sites throughout the state.  Since 2002, there have been twelve plantings evaluating a total of sixty-four (64) different taxa.  Trial plants are evaluated based on survival, growth, ornamental appeal, and their potential to be invasive over a five year period.  In 2002, we started with five co-operating sites including three private sector nurseries, Boxelder Creek Nursery (south of Hudson, CO); Harding’s (Calhan); and Little Valley (Brighton) and two CSU research sites, the Horticultural Research Center in Fort Collins (now ARDEC South) and Western Colorado Research Center – Orchard Mesa in Grand Junction.  Originally ten replications of each plant were planted in a randomized block design.   However, in later planting the number of replications was reduced to eight.

The 2015 trial planting at Little Valley Wholesale Nursery

Over the years some of the sites changed.  A major hail storm in 2009 destroyed the planting at Boxelder Creek and that site was lost.  In 2015, we moved the Harding’s Nursery site to the Colorado Agricultural Leadership Foundation near Castle Rock, CO.  Planting continues yearly. In 2015 we planted five taxa and in 2016 plan to plant another five taxa.  We continue to take growth and performance data on woody plants to determine if any merit introduction into Colorado and Rocky Mountain Landscapes with the Plant Select® designation.

Dr. Jim Klett taking data on the 2011 planting

Woodward Juniper (Juniperus scopulorum 'Woodward') a 2015 Plantselect® 

selection and part of the 2006 trial planting

Some of these woody plants have been recommended or introduced through the Plant Select® program including Acer tataricum ‘GarAnn’^PP15023 (Hotwings® Tatarian Maple); Arctostaphylos x coloradoensis (Mock Bearberry Manzanita); Arctostaphylos x coloradoensis (Panchito Manzanita); Heptacodium miconioides (Seven-son Flower) and Juniperus scopulorum ‘Woodward’ (Woodward Juniper).  I plan to highlight these and other plants which have stood out in the trials in future posts.

The 2006 plant at Harding's Nursery during the summer of 2014

Support for this project comes from Colorado Horticulture Research and Education Foundation, Plant Select®, Colorado State University Agricultural Experiment Station, and cooperating nurseries mentioned above.