In Bend, Oregon, we love our landscape trees.

One of the most common trees in landscapes around town is Quaking Aspen (Populus tremuloides), which is popular for quick growth, quaking leaves, paper white bark and beautiful fall colors. Taking a tour of town in the fall you can spot aspens everywhere, from Awbrey Butte and Northwest Crossing, to the east side near the Hospital. They’re cheap at local nurseries, easy to plant, and beautiful—and they’re the number one problem tree in Central Oregon.

Common Issues with Aspen Trees in Bend, Oregon

There’s a recurring list of problems with aspens locally, that make them hard to keep around in our landscapes for very long.

1. American Hornet Moth:

The American hornet moth (Sesia tibialis) is the number one aspen tree pest in our area. Female moths lay their eggs on the bark of aspen trees, and when they hatch, the larvae bore into the tree and create tunnels right above the roots. This burrowing damages the tree's vascular system, impeding the flow of nutrients and water, which can lead to weakened structural and increased susceptibility to diseases and other pests. Over time, affected aspen trees may have symptoms such as dieback, reduced growth, and even death if infestations are severe and left untreated. The tunneling can get so bad that large cavities can form at the base of the tree, just below the soil surface. This defect makes effected trees susceptible to falling in wind and snow storms. Effective management and early detection are important to protecting aspen trees from Hornet Moth in Bend. Signs of hornet moth infestation are small holes (about the size of a pencil eraser) a few inches above and below the soil surface, and foliage that is small and discolored.

2. Rapid Growth & Space Constraints:

Aspen trees grow vigorously—It’s one of the reasons we love them. They grow fast and provide shade and privacy, and look like mature trees in just a few years. The problem with this is, as Bend develops more densely with townhouses and smaller residential lots, aspen trees often get planted too close to structures and infrastructure. They outgrow their intended spaces, leading to overcrowding, root damage to structures, and competition with other plants for nutrients and sunlight.

3. Suckering & Shallow Roots:

Aspen trees are notorious for ruining lawns with their voracious root sprouts.It’s hard to enjoy your lawn with kids and dogs when it’s littered with rock-hard, fist sized hunks of root. Every veteran tree worker in Bend has had the experience of running the stump grinder through an entire lawn for hours, trying to grind out above-ground knuckles and roots. I’ve even seen aspen trees ruin paver patios if left alone for long enough. This above ground root growth can be expensive, and time consuming for homeowners and property managers to deal with.

Aspen suckers also rapidly colonize lawns, gardens, and other landscaped areas. The hundreds of tiny sprouts pop up like weeds in undesirable places around established aspen trees, which then have to be cut manually before the sprouts turn into a thicket of small trees. Unfortunately these tiny sprouts that get cut every year are important part of the aspens biology because they to bolster the root system of the “parent” aspen tree as it grows. By cutting back the aspen sprouts, we’re preventing the roots from keeping up with the growth of the parent tree and leaving the tree susceptible to uprooting.

Our Approach living with Aspen Trees in Bend

My first recommendation to living with aspen trees: “don’t do it".

…But, if you absolutely love the white bark and striking fall colors of your aspens, there’s a few things you can do to give them a better chance at surviving in the Bend Oregon’s climate.

Preventative Maintenance

Preventative maintenance is essential for the long-term health of your aspen trees, particularly in combating threats like the American hornet moth. Regular root inspections are a crucial, allowing for early detection of any signs of stress or infestation. During these inspections, look for symptoms such as reduced growth, die back, or unusual bark damage, which may indicate the presence of larvae. Small holes just above the soil level are a give-away that your tree has hornet-moth. In addition to monitoring, implementing an annual treatment regimen with beneficial nematodes is highly effective. These microscopic organisms are natural predators of the hornet moth larvae and can significantly reduce their population without harming the tree or the surrounding environment. They’re natural, and safe for kids and dogs. By applying beneficial nematodes to the soil around the base of the aspen trees each year, you create a biological barrier that helps keep the moths at bay. timing and application can be particular, so best to consult a certified arborist to get some information.

Site Placement

Choosing the right site for planting aspen trees is crucial for their success and longevity. Aspens thrive on larger properties where they have ample space away from buildings and structures. This minimizes potential damage to property from root systems and falling branches, and allowing the trees to grow freely. Ideal locations for aspen trees include areas near wet, acidic soils, which provide the moisture and nutrients they need. Additionally, aspen trees are known for their ability to propagate through root sprouts, a process that requires plenty of open space. Therefore, planting aspens in areas where root sprouts can naturally take over and expand is beneficial. It’s also important to avoid placing aspen trees too close to lawns, so that shallow roots don’t cause a lawn-care nightmare.

Managing Established Trees Near Structures

For aspen trees already established near buildings and structures, proactive pruning can help manage growth and maintain a safe size tree. Pruning should be done early in the tree's life cycle, ideally before the tree becomes too large. Early pruning helps to shape the tree and remove any weak or problematic branches that could pose a risk to nearby structures. By carefully thinning the canopy and cutting back overextended branches, you can reduce the tree's overall weight and improve its structural integrity. For trees in landscapes where root-bolstering sprouts can’t be encouraged, maintaining a smaller, lighter tree can reduce uprooting. Regular pruning also promotes better air circulation and light penetration, which can enhance the tree's overall health and resilience. When done correctly, early and consistent pruning can mitigate many of the risks associated with aspen trees growing close to buildings.

Spar Tree

Aspen trees might be a cherished part of your landscape, and they can be hard to manage. If you think you’re dealing with pest infestations, rapid growth, or extensive suckering, Spar Tree provides expert guidance or reliable tree pruning or removal service. We also have nematode application plan, to help your aspens thrive. Contact us if you’re interested.

We want to help you maintain a healthy, beautiful landscape.

Contact Spar Tree for consultation or estimate, or to learn more about our comprehensive tree care services in Bend, Oregon.

If you’re interested in exploring management of aspen trees, here’s some more reading:

 Urban Forestry South: Weigh the Pros and Cons Before Considering a Planting of Aspen

 Ross Tree Company: A Short Guide to Aspen Trees and Their Care

Where to Find Beneficial Nematodes in Bend