In an attempt to discourage homeowners from over-mulching trees, Riverside Village Forester Michael Collins, with the help of volunteers and experts, has provided an alternative in the form of “companion planting.”

In late April during an Olmsted Society workday, 16 volunteers planted 820 sedge plants – common oak and white-tinged — and nine Virginia bluebells among the half dozen bur oak trees in the triangular park at the intersection of Longcommon and Kent roads in the northeast part of the village.

“This has been a demonstration of companion planting,” Collins said. “We just want to put out an example of what’s possible.”

The oaks, said Collins, are all old-growth, pre-settlement trees – approximately 170 years old – that were once part of a large oak grove. Other oaks from the same era can be found near Blythe Park School. Eastgrove Road took its name from the area, Collins said.

“Mulching has gotten out of control a little bit,” Collins said. “It’s this volcano-mulching issue where things are piled up against the trunk of trees too excessively, where it’s actually doing harm to the tree rather than good.”

According to Collins, piling up more than a thin layer of mulch around the base of trees – “don’t do a volcano, do a doughnut,” said Collins — can suffocate tree roots. As the mulch breaks down, it can also pull nitrogen from the soil, away from the tree roots.

“So, there are negatives related to wood mulch,” said Collins.

The sedges, on the other hand, have long coexisted with oak trees and benefit them, said Collins.

“Ultimately, they’re a species that are flexible, that can handle dry and wet, so this is a good site for that,” Collins said. “The idea is instead of wood mulch, which actually pulls nitrogen from the soil to decompose and break down, their roots will actually retain moisture. It’s more of a symbiotic ecological relationship that started from the dawn of time.”

As the sedges spread, it also ought to make maintaining the triangle a bit easier, since weeds proliferate under the oaks right now. Cindy Kellogg, an Olmsted Society member who serves as the steward of both the Kent/Longcommon triangle and the larger Downing/Longcommon triangle kitty-corner from it, said it’s been hard to keep free of weeds.

“For the last couple of years I kept telling Mike, I think we ought to just dig this up and put turf in,” Kellogg said. “I just couldn’t keep it clean. I was frustrated.”

One of the six oaks in the triangle is showing signs of decline. While Collins said he hasn’t decided yet whether to take it down, he’s hoping the sedges that have been introduced can help slow the decline of the other old oaks.

On April 27, to mark Arbor Day the village planted a new bur oak, so if the ailing oak needs to come out, there won’t be a net loss. Other trees on the Kent triangle include shingle oaks and a Kentucky coffee tree.

Collins was inspired to try the sedge planting as a pilot after attending a meeting of the Chicago Region Trees Initiative and talking to Roy Diblik, perennial plant expert and co-owner of Northwind Perennial Farm in Burlington, Wisconsin.

Diblik’s presentation at the meeting was about companion planting instead of using mulch. Collins expressed interest in using the concept in Riverside, and Diblik volunteered to use Riverside as a test case that could be used as an example for others in the industry.

The plants themselves – which would have cost more than $1,000 wholesale — were donated by a company called Midwest Groundcovers in St. Charles, with whom Diblik had a professional connection. Diblik himself delivered the sedges, helped prep the site and directed the planting on April 27.

Because the companion planting is so costly, Collins said he’ll continue to use wood mulch in most areas in Riverside, but that companion planting could be expanded in the future if it proves successful at Kent/Longcommon and funding becomes available.

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