Growing Aspen Trees in Colorado

High in the Rocky Mountains of Colorado one can find an abundance of Aspen trees. With their brilliant white bark and green leaves turn shimmering yellow in the Autumn, their beauty is a magnet for visitors from all around the world.

An Aspen tree main trunk can live anywhere from 40 to about 150 years. The root system below ground can live for thousands of years and will produce lots of sprouts, commonly known as “suckers”. Aspens love lots of direct sunlight and new trees will have a very hard time growing when competing for sunlight.

If you’re a homeowner in Colorado and want the same beauty to gaze upon from the comforts of your own home, there are a few things to keep in mind. They won’t grow anywhere and can be quite a nuisance for some.

The Negatives

  • Expansive root system that will grow in all directions, and fast. The roots will spread a hundred feet from the main tree invading lawns, driveways, landscaping, and other plants.
  • New trees will sprout from the spreading roots. If left alone, you’ll have a grove of Aspen trees.
  • Susceptible to disease and fungus. Oystershell scale and Marssonina fungus are common.
  • Doesn’t like a lot of heat, and prefers cooler weather.
  • Does not do well at lower elevations (less than 7,000 feet).
  • Requires moderate water.

The Positives

  • Fast growing tree that can offer a good amount of shade.
  • New “suckers” have grown as much as 4 feet in one year.
  • Beautiful spring and fall colors.
  • Does well at higher altitudes, greater than 7,000 feet.
  • Moderately tolerant of short droughts.

Planting


Aspen Trees

Aspens do best in well-drained and non-compact soils, but can tolerate other soil types as well (just not clay or sand). Plant your Aspen in the Spring. This will give the roots plenty of time to establish themselves before the cold winter months.

Dig the hole twice as wide as the root ball and back fill with 50/50 native soil and some sort of soil amendment. This will help retain moisture and promote good root growth. They like full sun, so make sure you put them someplace that gets 6+ hours of direct sunlight per day. They can tolerate some 90oF heat, but not for long stretches.

Watering


Aspens love water. Really important to keep the soil moist with newly planted trees for the first 6 months. After the first year, you can water every other day in the summer, but are more prone to disease if the the tree doesn’t get enough water. When Autumn comes around, water less frequently, especially after the leaves have fallen. Let the first couple inches of soil dry out. It the winter, water once a month on days over 45°F.

Pruning


After about 4 years, you’ll want to start shaping the tree. In the winter, cut back the lower branches all the way to the trunk. this will make the tree grow taller. Remove any diseased branches and don’t let them sit on the ground. This promotes disease that can spread to the living trees. If two large branches are rubbing against each other, remove one to prevent damage to the tree bark. Aspens are fairly hardy, but if neglected, they can get into trouble pretty quick.

Disease and Fungus


Oystershell Scale
Oystershell Scale

I’ve had problems with oystershell scale on my Aspen trees on several occasions. This insect leaves behind a bumpy shell that’s about 5mm in size. If left untreated, the insect can kill the tree. There is a treatment you can mix with water and pour around the trunk base. The roots will absorb the treatment, and when the insect feeds on the tree it will die. You might need to gently brush off the scale the following year. There’s also an oil based spray for both dormant and active insect periods, but it’s a tough to apply on tall trees.

Marssonina fungus won’t kill the tree, but it does turn the leaves brown and can cause an early drop ruining the beautiful fall colors. The toughest part about the fungus is, you need to remove the dead leaves from the area, otherwise the fungus will come back the following year. However, if the tree has the right amount of water, this shouldn’t be a problem as it will naturally fight off the fungus.

Fertilizer


If you want, you can apply slow-release all-purpose fertilizer granules once in the spring time, but it’s not necessary. The Aspen tree can usually get all the nutrients it needs from the native soils.

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