Alternatives to Ash: The Research Bank is Growing

January-February 2012

Tom Invten, Canadale Nurseries, and I gave a seminar on this very topic last winter at the ISAO Annual Conference in London. It was interesting to note that several conference attendees came up to us afterwards to tell us about all the species they have been trialling on their urban sites. Many of you have been testing everything from Celtis to Taxodium and everything in between and several of you have had encouraging results. Biodiversity in the urban landscape is a goal we all share. Landscape Ontario has recently published this list of alternatives and they are listed on the next page.

What Exactly Should We Grow?
One of the challenges is that it takes 5-7 years to grow most of these trees in the nursery into a salable size for your needs. Most nursery growers will tell you that their requests for alternatives have been inconsistent and difficult to anticipate. They often carry alternatives and then have to destroy them because no one wants them, only to get a large order the following year. What can we do about this? This is a valid question and I would like to hear your suggestions for how we can communicate the need for certain species and cultivars for urban use.  

Sourcing Propagative StockAnother issue is that some of the species we list are not always easy to source in the trade. That could be due to low availability of propagative stock (seed, understock, scion material) or difficulties in production including slow growth and poor transplant success due to poor rooting (e.g. Carya). The good news is that we have research institutions looking at solving some of these issues. For example, the University of Guelph Arboretum Horticulturalist Sean Fox has been working diligently to establish a blue ash seed orchard. Sean has also conducted trials germinating blue ash seed (a historical challenge) and has found his stratification methods to be very successful and not at all as dismal as the literature may suggest. 

Another example is the number of growers and researchers trialing new methods of production that allow for more branching and the development of a more fibrous root production on difficult to transplant, tap-rooted species such as Carya and Quercus species. Niagara College in Niagara-on-the-Lake, Ontario has been looking at this technology for the last few years and their students are actively participating in these projects as part of their education.       

A Life-Long Mission
Alternatives to ash are something you are going to hear about more and more. The research group is in the process of writing photo-rich articles and factsheets for the Landscape Ontario website and magazine (Horticulture Review). We hope to encourage more dialogue and problem solving on the topic and we hope to learn from each other what species and cultivars we should be growing and planting in the urban landscape. I think this will be one of those life-long missions that remains near and dear to our tree-loving hearts. 

List of Ash Alternatives (from Landscape Ontario)
Acer campestre Hedge Maple
Acer x freemanii Freeman’s Maple
Acer ginnala (A. tataricum subsp. ginnala) Amur Maple
Acer platanoides Norway Maple only cvs.: ‘Columnare’, ‘Crimson King’, ‘Globosum’ & ‘Royal Red’
Acer triflorum Three-flowered Maple
Aesculus flava (octandra) Yellow Buckeye
Amelanchier spp. Serviceberry
Carya cordiformis Bitternut Hickory
Carya ovata Shagbark Hickory
Celtis occidentalis Hackberry
Fraxinus quadrangulata Blue Ash
Ginkgo biloba Ginkgo
Gleditsia triacanthos var. inermis cvs. Honeylocust
Gymnocladus dioica Kentucky Coffeetree
Maclura pomifera Osage orange
Malus spp./cvs. Crabapple
Ostrya virginiana Ironwood
Phellodendron amurense and/or sachalinense Amur Corktree
Pyrus calleryana cvs. Callery Pear
Quercus bicolor Swamp White Oak
Quercus ellipsoidalis Northern Pin Oak
Quercus macrocarpa Bur Oak
Quercus muehlenbergii Chinquapin oak
Quercus shumardii Shumard Oak
Syringa reticulata and/or pekinensis spp./cvs. Japanese Tree Lilac
Taxodium distichum Baldcypress
Tilia Americana Basswood
Tilia cordata Littleleaf Linden
Ulmus americana American Elm

Our mission is to enhance and promote the care and benefit of trees for present and future generations in Ontario through education, research and awareness.