Trees. They are all around us. In our gardens. In our parks. On the street. Yet we barely notice them most of the time. Gardeners tend to forget that they are plants like any other. Non-gardeners tend to regard them as more or less permanent objects in the landscape.
I’ve recently been helping with the Al Rollinger Tree Survey being done by Denver Botanic Gardens and The Denver City Forester’s Department. (For more information on this, see www.botanicgardens.org/rollinger-tree-collection-50-year-survey-project.) This has taken me to different parts of the city, looking at trees in yards and on the street. For each tree in the project we identify the tree, measure its diameter and height, assess condition, take a photo and get the GPS location. This close examination has given me a new appreciation of these giants of the plant world.
Denver is at the western edge of what was once short grass prairie all the way to Kansas City. Trees are not native to this landscape apart from the odd plains cottonwood near water. All the trees planted and growing in our city are imported here, whether from the higher ranges in the mountains (pine, spruce, aspen) or from the north and east (maples, oaks).
Why plant and grow trees?
Yes, it can be difficult to grow healthy, long-lived trees here. Too little water, alkaline soil, heavy clay, too hot in summer, too cold in winter, traffic pollution, concrete and blacktop suffocating roots. These are the same problems that challenge us in our back yards as we try to get our shrubs and flowering plants to perform for us. But with a little care and attention, we can grow healthy trees. Just look at the many benefits trees bring:
- Provide oxygen
- Reduce carbon dioxide levels
- Improve air quality through absorption of pollutants
- Absorb and retain water to reduce run-off and delay onset of peak flow (flooding)
- Reduce soil erosion
- Improve capacity of soil to absorb water
- Provide animal, bird and insect habitat
- Reduce noise levels
- Reduce stress
- Reduce UV exposure
- Shade and cool our homes and streets
- Save energy (natural cooling through shade v. AC)
- Provide wind breaks
- Increase property values and reduce crime
- Improve walkability of neighborhoods
- Provide beauty
Get to know our trees
You can find out about every single tree growing in the street and public rights of way in Denver by typing in an address in the city’s “Treekeeper” program at http://beasmartash.org/do-i-have-an-ash-tree/interactive-map. When I walk the dog around the neighbourhood, I look up now and try to identify the trees I walk by (or underneath). If I don’t know one, I take a note of the address and check on the Treekeeper when I get home. (Because of the vast amount of data involved, the program doesn’t work well on a mobile device.)
Some trees are “champions”. These are trees that have attained a large size (based on species) through girth, height and crown size. You can find out about Colorado State Champions here www.coloradotrees.org/wp-content/uploads/2016/06/2016-Website-Champs_Alpha.pdf and National Champions here www.americanforests.org/explore-forests/americas-biggest-trees/champion-trees-national-register/.
Choosing and buying a tree
A tree can be a big financial investment and selecting the appropriate tree is very important if you want it to not just survive but to thrive for many years. The CSU Extension Service publishes a very helpful list of trees recommended for the front range. You can find it here: www.extension.colostate.edu/docs/pubs/garden/treereclist.pdf
The non-profit organisation, The Park People, has a scheme called Denver Digs Trees for selling street and yard trees at subsidised prices (or even for free in some locations) every year. The trees they sell are all considered suitable for Denver. You complete an application form in January or February and the trees are distributed in mid-April. They will even come and plant your tree for you if you need help. You can find them here: www.theparkpeople.org/Programs/DenverDigsTrees.aspx
Look for trees in Colorado nurseries and garden centers which grow their own trees. A tree which started life here is likely to be better adapted to Colorado growing conditions than one imported from another state.
Before you plant
When planting a tree whether in your yard or the street, you need to get the position of all utility lines checked before digging . You can get the utility lines checked for free by calling 811. You also need a permit from the City Forester before you plant a tree in the street i.e. the public right of way. The permit is free and can be obtained by email. See here for details:
Like all plants, trees can have problems. Pests and diseases or hazards caused by natural events, like storm damage. Often problems stem from human actions. Improper planting, insufficient or too much irrigation, damage from garden tools like mowers and weed-whackers, root damage from nearby construction, damage from staking and guy wires, pet damage, root damage from landscape fabric or inappropriate mulching e.g. river rock.
Emerald Ash Borer
The biggest problem facing trees in Denver right now is the threat of the Emerald Ash Borer (EAB). This pest came from Asia where their ash trees are immune to it. Unfortunately, American ash trees are not. Its presence has been confirmed in Boulder since 2013 and in Longmont since 2016. It threatens to wipe out all the ash trees in Denver if (when?) it gets established here. That’s 1 in every 6 trees in Denver or 1.45 million trees. For information and advice about EAB go to http://beasmartash.org/.
To try and mitigate the effect that EAB will have on our city trees, the City Forester’s Dept, in association with The Park People’s Denver Digs Trees program, is offering new street trees now for FREE. By planting in advance of the arrival of EAB, the aim is to mitigate the effect of the EAB and increase diversity in the city’s tree population. You don’t need to have an ash tree already or any kind of street tree, just room to plant a new one. To apply for a new street tree, go to www.beasmartash.org/what-can-i-do/apply-for-a-tree/. They will even plant it for you!
Learn more about trees and get involved
The Park People run a program with Denver’s City Forester’s Dept which trains volunteers to become Community Foresters. Volunteers assist the City Forester’s Dept by becoming qualified to lead and participate in tree planting and tree care projects in their neighborhoods. Courses are run every year. More information can be found at www.theparkpeople.org/programs/communityforester.aspx
Get more information about trees
You can find useful information and get advice on all aspects of trees from the following:
Your local City Forester (arboreal inspector) – find him/her at www.denvergov.org/content/dam/denvergov/Portals/747/documents/forestry/forestry-inspections-districts-map.pdf
CSU Extension Service ‘Ask an Expert’ – ask.extension.org/groups/1955/ask
Ask a Master Gardener – www.cmg.colostate.edu/ask-cmg.shtml
The Park People – www.theparkpeople.org
The Colorado Tree Coalititon – www.coloradotrees.org/
A professional arborist – see the list of arborists licensed to operate in Denver at www.denvergov.org/content/dam/denvergov/Portals/747/documents/forestry/DPR-Forestry_current-licensed-contractors.pdf
Look up, learn more and enjoy our trees!
Anne Hughes/A Denver County Master Gardener
Photo by Anne Hughes