If you’ve been on a drive through the Rocky Mountains, you have certainly seen patches of aspen trees here and there. Their leaves change color from green to gorgeous gold in the fall and they are some of the most beautiful trees in Colorado.
Just because they’re common in Colorado, doesn’t mean they are necessarily easy to take care of. That’s why we put together this guide so you can keep your aspens looking amazing.
Read on to find out more about the life span of aspens, some common diseases, and best practices for a happy healthy aspen patch.
What Are Aspen Trees?
Aspens are a classic colorful Colorado favorite. They are some of the most beautiful and widespread trees in Colorado, especially in the mountains. There are more aspens here than in any other state! People from all over the world travel to the Rocky Mountains every October to see these gorgeous trees change colors from deep greens to magnificent golden yellows.
Belonging to the Populus (willow) family, aspens have many other brothers and sisters you may have noticed in Colorado. Some of those include poplars and cottonwoods. These trees are loved for their beauty, shade, and even erosion control. This doesn’t mean they’re easy to maintain though. We’ll talk more about that later. Also, it’s important to note that an aspen tree isn’t a willow tree, but they are related.
What does an aspen look like in its natural habitat? Aspens naturally grow in low creek bottom areas and need an outstanding 26-28 inches of rainfall every year to stay happy. An aspen tree will live for about 10-15 years in a residential setting in the front range of Colorado. They can live up to 150 years in the wild with the right conditions, according to the Forest Service.
Although they thrive naturally in higher elevation areas, with lots of extra special care your aspens can thrive down in the city as well.
common aspen tree issues
1) Aggressive Propagators
You may plant an aspen tree in your outdoor living space, and somewhere down the line you look again, and it’s multiplied! No, there’s nothing wrong with your vision. These guys can be very aggressive, shooting roots under, out, and back up as far as 30 feet away!
You’ll want to be extra cautious with where you place them, or your neighbors might have some unwanted aspen trees pop up in their yard. Surprise trees aren’t always the best gift to give. Avoid areas around your house’s plumbing and walkways. These guys have no problem making the middle of your sidewalk or your septic tank their new home.
When you notice little baby aspens coming through the ground, you can cut them down. It’s not a good idea to use root killer though, since this small tree is connected to the bigger tree, and chemicals would destroy the whole family. Many people simply run their lawnmowers over the sprouts and are fine with that.
2) Cytospora Cankers
Phase 1
Striations
Phase 2
Canker Development
Phase 2 (cont.)
Oozing, discoloration
Phase 3
Pycnidia spores
Phase 3 (cont.)
Fruiting bodies
Phase 4
Desiccation
Cytospora cankers can be some nasty stuff and it spreads quicker than a bad case of the Mondays. Unfortunately, this is the number one killer of aspen trees in Colorado. Our expert says if you notice these orange marks/spots on your aspens, consider it an emergency and remove that tree ASAP. Be proactive and remove any infected branches. If not, you risk losing any other aspens you may have, as well as other trees in the Populus (willow) family.
If your aspen tree comes down with a case of Cytospora, unfortunately, there’s no hope of recovering the tree. It must be removed immediately before it starts infecting the other trees around it. Cytospora is an airborne illness and can infect many trees quickly with just a gentle breeze. Remember, a sick aspen can make their other brothers and sisters in the Populus (willow) family sick too.
3) Hypersensitive to Molding and rotting leaves
Part of our complete Colorado landscaping timeline includes raking up the leaves. This is especially important with aspens. Every year, you can see the magnificent golden amber leaves turn just before they dump all over the ground.
The leaves have a tendency to start growing some funky stuff, and, if left unkept, could rot and ruin your happy aspen family. So, remember this extra care is essential to successful growth.
4) Insects think aspen trees are like caviar
What better home than the soft, luxurious bark of an aspen tree if you’re a little critter? Easier to infest than harder trees, aspens tend to see lots of insect problems. Ready for another double whammy? The more a tree is stressed, the more insects will be attracted to it.
These trees are quick and easy to stress out, so again, be quick to give us a call if you notice any bugs bothering your aspens. We’re happy to look at the tree, see if it can be saved, recommend solutions, or remove the tree if needed.
5) Other Diseases
Can you believe there are over 50 insects and diseases that affect aspen trees? Part of owning an aspen is having a removal plan in place in case of any diseases.
We could go over them all in detail, but the plan is typically the same for whatever makes your aspen sick – remove the tree as fast as you can. There may be hope in saving your aspens, like in cases of underwatering, but when an aspen gets sick- especially with Cytospora, the only safe solution is to remove the tree before it infects the others.
Caring For Aspen Trees
So, you’re confident that you’re ready for the challenge of owning happy aspen trees- let’s make sure your shimmering ladies are set up for success.
Make Your Aspens Feel At Home
Trying to recreate the same environment these trees naturally grow in is your best bet to pulling this off. You’ll find aspens huddled together along creeks in the wild, typically in a valley. Since it snows in the mountains, these trees are naturally cold hardy to zone 1, so they can handle the winter just fine.
Aspen patches tend to be dense, with trees growing just a few feet apart from one another. Their roots are connected as the tree aggressively propagates. You can cut down these little babies as they pop up, but aspens become stronger the bigger their family gets. Consider an area where you could allow a few aspens to pop up nearby.
To simulate a creek bed, you would want to make sure there isn’t any clay in the ground for at least 24 inches and keep the soil very moist. You even build a berm for the trees (a mound of the earth or wall around the tree to keep the moisture in) with mulch to make them feel right at home.
Watering Your Aspens
Aspens love two things: year-round moisture and loose soil. This is where things can get tricky. Keep their roots moist, but not their leaves. Watering the leaves increases the chances of rotting, which is already a high probability due to the delicate nature of this tree. You don’t want them to get sick and spread to other trees.
Make sure your aspen stays moist. If the soil dries out, your aspen is already suffering inside as it needs constant moisture to stay happy. So, you might as well water these guys every day. Be sure to winter water if dry once per month. Building a mulched berm or tree ring could help keep moisture in. Irrigation systems are a great idea for aspens.
When To Prune Aspens
If you notice a branch starting to die back, prune it off. It’s better to get those diseased branches removed before the sickness spreads. You’ll want to keep an eye on your aspens year-round and have someone come out ASAP if you need help pruning or tree removal.
Our experts recommend regular pruning every year for aspens (more if you notice dieback) in the winter. You’ll want to prune any branches damaged from heavy snowfall too. When pruning, you’ll want to cut branches back all the way to the trunk. Keep the best-looking branches and remove the worst looking and your aspen will thank you.
If you notice a diseased branch throughout the year, cut it back to the collar immediately and do not wait until winter. It’s important to remove diseases from the tree before they spread.
Aspens - High Maintenance, High Payoff
As you can see, aspens require a lot of special care but can be a gorgeous addition to your landscape. Remember, lots and lots of water will help these guys stay happy.
If you notice any diseases like Cytospora Cankers, be ready to remove the tree so it doesn’t spread quickly. Also, have a mitigation plan in place because aspens are very aggressive in propagating themselves.
With lots of love, these trees will bring you joy for many years to come with their quaking leaves rustling in the breeze and golden shine brightening up the fall season.
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