Growing Aspens in Colorado

Aspen Trees

Aspen Trees

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

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

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.

The cons:

    • Expansive root system that will grow everywhere, 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 Aspens.
    • Susceptible to disease and fungus. Oystershell scale and Marssonina fungus are common.
    • Doesn’t like a lot of heat, and prefers cooler weather.
    • Thrive better at an altitude above 6,000ft.
    • Requires moderate water

The Pros:

    • 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 extremely well at higher altitudes, those above 7,000 feet.
    • Not too difficult to care for.
    • Moderately tolerant of droughts

Planting

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. 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 90°F 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 it sit on the ground. 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 several times. This insect leaves behind a bumpy shell that’s about 5mm in size. If left untreated, this 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.

There is also a spray for the Marssonina fungus. Although the fungus won’t kill the tree, it does make the leaves look ugly. It’ll also cause them to drop early and you’ll miss out on the Autumn 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.

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