Kinzler: Addressing commonly asked tree questions

In this week's Growing Together column, Don Kinzler tackles several frequently-asked questions about a wide variety of trees.

Most poplars have a relatively short lifespan of 30 to 40 years.
Abby Makay/The Forum
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On a newly planted tree, if you tie a ribbon around a branch that’s currently three feet above ground level, and the tree grows an average of twelve inches in height per year, how high will the ribbon be in ten years?

It’s a classic trick tree question, because the ribbon will still be approximately three feet above ground after ten years. Tree height is added at the top of the tree, not at the base, and a branch three feet above ground remains at that location.

Although the previous riddle isn’t a real question, I receive many emails about trees and I thought it would be interesting to share a few of the most frequently asked questions, along with brief responses.

Q: My Autumn Blaze maple has cracks in the trunk and the leaves are looking yellow and sickly. Is it a disease, and should I be spraying it with something?

A: Autumn Blaze maples would be happier in the naturally forested areas of Minnesota and eastward. They’re sensitive to soil type, and often resent being planted in the Red River Valley and westward, where the soils are more alkaline. Consider them a roll of the dice, doing well in some locations while barely limping along in other sites.


Q: The leaves on our silver maple are quite yellow. I’ve heard it’s iron deficiency. Can this kill the tree?

A: Maples and a few other species struggle to access soil iron and if the deficiency persists long enough, trees are weakened, becoming susceptible to winter injury and attack by disease and insects. Treat with iron products available from garden centers following label directions. Yearly treatments are often required.

Iron deficiency chlorosis is common on many maples, causing the yellowing of leaves.
Abby Makay/The Forum

Q: Our maple leaves have round, red bumps on them. I tried spraying, but they are still there.

A: The bumps are maple leaf galls, caused by tiny insect-like mites, which encase themselves inside this tissue, safe from insecticide sprays. When the galls appear, it’s too late for treatment. Luckily, the galls are mostly cosmetic and the tree’s health is usually unaffected.

Q: My ash tree has two main trunks, forked in the middle, and a crack has formed down the middle. Can you tell me if the tree is safe, or if it might split apart?

A: Determining whether a tree situation is structurally safe or sound should be addressed by a certified arborist who is trained in the field of Tree Risk Assessment. Some split trunks can be bolted together, but assessing the safety of the situation requires special certification.

Q: Can I plant trees and shrubs in the fall, or is it better to wait until spring?

A: Planting trees in September is highly successful, as the root system continues growth, giving a head start versus waiting until spring.


Q: The lower limbs on our linden have been hitting me every time I mow. Is now in September a good time to remove some of the lowest branches?

A: Pruning is better done in early spring before growth begins. Pruning cuts made in fall don’t “heal” the way they do in spring, leaving exposed wounds susceptible to winter tissue dieback.

Q: Several branches on my cotton-less cottonwood poplar are dead and I’m afraid it’s got a disease. If I prune out the dead branches, is there something I can do to save the tree?

A: Cotton-less cottonwood poplars are fast-growing, but have an average lifespan of only about 30 to 40 years. Dead branches signal the beginning of the end, and unfortunately there isn’t a way to reverse nature’s course. Enjoy them for their rapid growth, and replace when their time is up.

A seedling elm has become established inside a purple-leaf ninebark shrub.
Abby Makay/The Forum

Q: Our elm tree drops millions of seeds each year in our flowerbeds and pots, and they quickly sprout. Is there something that can be done to prevent all these little nuisance seedlings?

A: Elm seeds have no dormancy, and can sprout immediately upon dropping. They’re especially annoying when they sprout among established perennials or shrubs. Besides hand-pulling and digging, pre-emergent herbicides can be tried such as Preen, but control can vary.

More gardening columns from Don Kinzler
In this week's Fielding Questions, Don Kinzler offers advice for caring for a weeping fig, tips for thinning apples, and tells readers it's not too late to wrap trees to prevent sunscald damage.

Don Kinzler, a lifelong gardener, is the horticulturist with North Dakota State University Extension for Cass County. Readers can reach him at
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