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20 March 2009

COLORADO COLLEEN: Urban Aspens

Aspen trees don’t fare well in city environment, where hot temperatures and heavy clay soils prove detrimental to their well being. Plus, they can’t filter air pollution effectively. Injury by hail, pruning and other elements render aspens susceptible to fungus, and other diseases readily set in. Quaking Aspen is the most typical species. Big Tooth Aspen can be found, but is rarely commercially available. Aspens don’t make good street trees, but can make nice accent trees in yards.

For those who want urban aspen, note the following considerations:
* First, make sure you’re selecting and planting a tree with a well developed root system. A lot of aspens are collected from the mountains, and sometimes the trees don’t have much of a root system.
Ask questions about where the aspens came from and when. If the trees are in containers, look at the bottom of the container to see if you can see roots. Sometimes, the aspen are collected with they’re much younger, but if they’ve been growing in the nursery for a year or two, they would have a more developed root system.
* Another key factor in successfully growing aspen is finding the correct site. Don’t plant them on the south side of a house or anywhere the tree will get a lot of reflective heat from the street, sidewalk or buildings. Aspens are prone to sun scald.
* Amend the soil. Aspens typically grow in decomposed granite. The key to successful growing is well drained soil. Local soils tend to be heavy clays, but they can be amended with organics.
* Water slowly and deeply. Aspen growing in their native habitat get a lot of moisture. Aspen in the city need a good watering regime. Water every couple of days after the soil has dried out--about every three days during summer. Like all plants, aspens need water, but also oxygen. If the site is constantly wet, the trees won’t get the oxygen they need.
Other caveats:
* Due to the big, woody roots that connect trees, aspens tend to produce sucker growth, especially when placed close to lawn areas. Aspen can fill in, so keep them in isolated beds filled with other plants or heavily mulched and you’ll have less of a problem. Do not mulch with cedar.
* Aspens are the shortest living tree species in Colorado. People growing aspens in the city should view them as 20-30 year plant. Some live longer, but not many.
* Be aware that aspens are prone to twig gall disease and leaf spots, both fairly difficult to control.
* For information about aspen trees, visit Plant Talk.

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