Allen Wilson: Learning how to keep aspens healthy

Question: We have a number of beautiful and healthy quaking aspens in our yard. Of course, we get suckers or sprouts growing everywhere, which I simply prune at ground level.

However, we have a couple that have appeared in places ideal for new trees. If I leave these alone, will they grow into mature trees or will they just become a bigger problem?

Answer: Yes, they will grow into trees just like the mother tree. This is the natural way for aspens propagate.

When you see a grove of 100 or so aspens in the mountains, chances are they all started from a single tree. Aspens have a system of underground horizontal stems called rhizomes. It is not unusual to see an aspen sprout from a rhizome 20 feet from the mother tree. I was told by a forester that aspens have more stems under the ground than above ground. That is why they produce so many sprouts.

Aspens are a relatively short-lived tree. A life span of 10 to 20 years is normal. The sprouts are compensation to continually keep new plants coming. Sprouts will come from these underground stems ever after all trees have been removed.

I had a group of about 10 aspen trees in my yard and was diligent in removing all the suckers or sprouts. When trees reached about 13 years in age, they started dying. I wished I had started five years earlier to let one sprout grow beside each tree so they would have been a decent size when the mother tree died.

Aspens also grow from seeds. Plants sold in nurseries are all from seed. So each tree is unique.

Besides the continual sprouting, aspens have disease called aspen leaf spot (Marssonina brunnea). Black spots appear on the leaves in the spring. If spots are numerous enough or grow large enough, leaves turn yellow and fall off. Trees usually develop new leaves to replace the ones which have dropped.

Spring infection of new leaves comes from spores left behind on last year’s old leaves. The best way to prevent aspen leaf spot is to clean up all fallen leaves and dispose of them. A fungicide, such as Daconil, can be applied as the new leaves emerge in the spring for extra protection.

I’ll have more information about aspen trees in next week’s column.

Allen Wilson can be contacted at