Growing Aspen Trees #704118 - Ask Extension


Growing Aspen Trees #704118

Asked July 22, 2020, 5:10 PM EDT

When should I plant an Aspen tree from Colorado in southwest PA? How can I protect it from insects and fungus?

Westmoreland County Pennsylvania

Expert Response

Good morning, and thank you for your question. Following is information on aspen trees and how to grow them. From reading this, it seems that aspen are a very difficult tree to grow in a residential setting.

The aspen (Populus tremuloides) is an iconic keystone tree species, and its mixed understory supports a diverse ecosystem throughout the higher elevations of the Rocky Mountains.

Aspen trees naturally grow in groves, rather than as individual trees.

In an ideal setting, aspens remain healthy and resist damage while spreading roots and sprouting new trees from them. But in residential or commercial settings (such as the landscape surrounding your home or business), problems can severely affect aspen health and appearance.

For example, the aspen is commonly affected by:

  • insect pests
  • fungal infections
  • animal browsing and injury
  • drought and heat
  • fire suppression and conifer growth

However, the biggest problem aspens face in an ornamental landscape is the soil it’s planted in.

The Importance of Soil Quality for Aspen Health

Many aspens are planted in the landscape surrounding a home (often within 10′-15′ of the foundation). The problem is that there’s no good soil in that area. When we build our homes, we excavate to put the foundation in. The area around it is then backfilled with the mix of material that was dug out of the hole to put in the foundation. This mixture isn’t topsoil and it’s certainly not what aspens need (it’s nothing like what’s found in the drainage areas of mountain climates where aspen thrive).

But that’s just the beginning. Aspens need to clone themselves to stay healthy (that’s why they naturally grow in groves). They do this by sending out tons of “suckers,” many of which end up in spots where homeowners don’t want them. So, we cut them out or let the elk/deer eat them to the ground. Either way, the aspen can’t grow to put out more leaves that would help them combat stressors, such as insects and disease.

As a result, aspens have the most problems of all our local plants. In fact, they seem to be perpetually afflicted by a new problem, no matter how many or how often treatments are applied. And it all starts with how and where they’ve been planted. When something starts out in a bad way, rarely will it improve.

Can I improve the soil / environment for my aspens?

The US Forest Service says that the tree grows best in the "moist but well-drained, slightly acidic soil found at higher elevations," writes Robert Cox, horticulture agent at the Colorado State University Cooperative Extension. Assuming your aspen’s already been planted, there are two things you can do to improve its chance of success.

First, have a tree care professional apply a soil injection that includes a blend of fertilizers and nutrients to improve soil health, as well as a systemic product to get rid of insects and mites.

Second, protect the young shoots so the aspen can help itself. Sometimes it’s as simple as not cutting them out but you can also put up a physical barrier to prevent deer or elk browsing.

Aspen do not tolerate shade and can sprout in full sunlight.

Plant Talk Colorado, a publication of Colorado State University, says that aspen planted in urban settings do best on the north and east sides of buildings. However, it adds that aspen are generally difficult to grow in the urban landscape because the soils they like are rare and because of their susceptibility to disease and insects.

Here is a list of more potential aspen problems:

  • Aphids.
  • Ink Spot Disease.
  • Marssonina Blight.
  • Aspen Leaf Miners.
  • Sawflies.
  • Elk Scarring.
  • Western Tent Caterpillar.
  • Oystershell Scale.
  • Poplar Twiggall Fly.
  • Black Canker.
To find out about treatments for these conditions, there are any number of sites that will give you this information. Please try to select those that recommend organic and cultural remedies if you encounter any of the problems listed. 

I hope this information has been helpful to you. 

Jeanne Quintavalla Replied July 23, 2020, 11:15 AM EDT

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