Testing could provide insight into sustaining Triangle Park trees

By Audrey Posten | Times-Register

Testing could provide insight into best practices to manage and sustain the trees in McGregor’s Triangle Park. 

Julia Badenhope, a professor of landscape architecture at Iowa State University who has aided the city through the Iowa Living Roadways Community Visioning Program and now its Mending/Bridging project, is offering input on the process and even students to help conduct the tests.

The trees’ health have been a focal point of recent discussions between McGregor’s Parks and Green Spaces Committee and other community members who are seeking to find a balance in protecting the vital downtown green space while also holding events. 

It also comes at a time when the city is preparing for the 2026 reconstruction of the brick streets around Triangle Park—including re-laying of the bricks and addressing the underground infrastructure—as well as enhancements to the park itself to improve functionality, aesthetics and accessibility.

Badenhope said urban tree success is one of her focuses. 

“I actually teach a class on urban tree and plant and soil technologies, basically teaching my students how to think about trees and plants and soils as integral parts of the city that have to be designed to succeed,” she shared at an August Parks and Green Spaces Committee meeting.

According to Badenhope, urban trees often live just seven to 10 years because they lack adequate soil to support their size.

“Trees have to have enough rooting area to get enough water and nutrients to support that canopy. Urban trees rarely get that,” she said.

Badenhope explained tree roots don’t grow as deep as most people imagine. Instead, they’re generally two feet deep and spread out around the tree, like a big, flat plate.

“That flat plate supports the tree and keeps it solid on the ground. The top grows and will make new tip growth when the roots grow. If you have a really small area for the roots to grow and they occupy all the space, they can’t grow. That means the top can’t grow and that means it starts to die,” she said.

The trees in Triangle Park have well surpassed the typical urban tree life span. In fact, they were planted 50 years ago this fall, after five towering elms previously growing there were lost to Dutch elm disease. Although still not mature, die back is visible at the tops. 

“If we look at those species and we did a little soil study, we could see how deep the soil is and figure out the total soil area available to those trees. I think you’ll find, for the number of trees and the species of trees you have, you may not have enough soil volume to let them grow to maturity,” Badenhope said. “That doesn’t mean they’re doomed, but it does mean there are some challenges that have to be solved.”

Another issue is compaction, which lessens the volume of air and water available to the tree. It’s one reason vendors for the arts and crafts festivals previously held at the park were moved off the grass.

Limited air and water disrupts the delivery of nutrients to the tree through microbiology— worms, bacteria, fungi, microorganisms. 

“If you don’t have air and water, you can’t have those microbes that process the minerals,” Badenhope said.

She shared several options to mitigate compaction, including soil management through a method called radial trenching. Using a power air stick, this opens the soil by trenching out from the tree trunk to a depth of around one foot. Afterward, compost is added to the soil, then replaced. 

“The next time you do it, you choose different spots. So, periodically, you’re going in and you’re actually refreshing the soil—adding new biology, adding lots of organic matter and giving a little more oomph to the soil ecology,” Badenhope explained.

Along with maintaining the soil, it can be reinforced with fibers that help manage compaction.

“Soil scientists are making a really juicy, composty mix, and then they’re mixing in fibers and creating a new surface layer that’s a little more resistant to compaction. So there are a combination of technologies you can use,” Badenhope detailed.

Badenhope stressed she isn’t making decisions about the trees for the community, but rather helping people understand the problems and facilitating discussions to determine potential solutions. She suggests documenting the trees—what they are and how big they are—and then determining soil volume. Her students are slated to come to McGregor in early October to help with this.

“The next thing I would have them do is some soil pits and do some tests. A pit might be 18 inches square. We would go down three feet. Then we’ll look at the condition of the soil that’s there and maybe choose a couple locations so we can see if it’s similar or different in different places,” she said. “Then we would do a percolation test where we would pour in water and see how fast the water leaves there. That would tell us if there’s something confining water movement and so forth.” 

Samples from the pits will be sent to a lab for assessment. This would run the city of McGregor $400, but all other services are at no cost. The students could even devise solutions to help McGregor move forward. 

At the least, said Badenhope, the information can be provided to the landscape professionals who will assist with Triangle Park enhancements.

McGregor Economic Development Director Brandi Crozier values the insight.

“I wanted [Julia] to come here because she’s very sensible and she has no bias in any of this. I think her work, along with that of consultants, will lead us to a positive outcome,” she said.