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Answer Man: Could clear-cut mowing hurt monarchs?

August 22, 2018

Given the rate these monarch caterpillars mow through milkweed leaves, it’s important not to mow down all the plants in ditches and roadsides or they’d never survive long enough to transform into eye-catching orange and black butterflies.

Oh, All-Knowing Answer Man, my neighbors and I have been raising monarch butterflies this summer and were sad to see that ditch mowing has begun. The mowing is removing the milkweed monarchs need to lay their eggs and that larvae need to grow. I know you’re astute about things like these. Can you tell us if there is any protocol on ditch mowing other than to clear-cut the ditch?

Your fan — Michael Pagelkopf

It’s funny you should mention monarchs, Michael, because just recently the Post Bulletin published a feature on a 15-year-old who has raised and released more than 220 of these butterflies this summer.

If you and your neighbors have had anything like his success, I can see why you might be worried about the loss of milkweed from mowing.

According to Rochester’s tall weed and grass ordinance, property owners must maintain their lawn and any adjoining right of way (the space between the sidewalk and the street) at a maximum of 10 inches in height. For most city property, that boils down to clear-cutting regardless of what might be growing there.

But don’t say goodbye to your butterflies just yet, because City Forester Jeff Haberman says there is a way around this when it comes to native plants.

Property owners who want to maintain an area on their property in excess of the ordinance can apply for a natural landscape permit, which would allow you to maintain growth of native plants on part of your property. If you wanted to protect an area of milkweed growth on your property, that’s what I’d suggest for you and your neighbors. I’ll link to the form online.

Haberman says the few “ditch” areas that the city mows (mostly frontage roads and medians) are clear-cut for safety reasons.

“Basically, if we allowed them to grow there would be problems in sightlines for intersections and traffic,” he said.

However, Haberman says Parks and Rec also maintains more than 20 natural prairie areas that provide habitat in what is likely a safer and more monarch-friendly environment than a center strip along the highway.

All this information begs the question: does ditch-mowing really remove that much habitat?

Mike Dougherty, Minnesota Department of Transportation spokesman and man of the mow-ment, says probably not.

According to Dougherty, most of the ditches MnDOT maintains along highways and interstate really don’t have enough milkweed to justify leaving them to grow. But where recent construction has disturbed the soil, mixes of native plants will be seeded in and can result in growth of milkweed. In those areas, Doughterty said, the ditch could be protected as part of MnDOT’s ongoing effort to provide habitat for pollinators (such as monarchs) in the approximately 175,000 acres of Minnesota green space it manages.

To protect those native plantings, “no mowing” signs may be posted or prescribed burn treatments may be used.

Dougherty says a few of these no-mow areas can be spotted along Interstate 90 or Interstate 35 where milkweed is mixed with native grass and wildflowers. It’s habitat for more than just butterflies, too, which ends up being better for the environment overall.

Dougherty says the decision to mow or not to mow ditches often comes down to safety. It’s a tradeoff, he says. While it would be nice to protect milkweed everywhere, that’s sometimes impractical or a safety risk, particularly at intersections.

“In the end, we’ll see if there is any sort of safety issues,” he said. “If it’s truly just a ditch, we’re just mowing as we normally do at the right height.”

To make up for it, Rochester and MNDOT both compensate by creating protected areas where native habitat for monarchs (and other wildlife) can be maintained. And usually those areas are a little safer for monarchs in the long run.

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