Cali Garzon, left, and Neva White of Spark-Y Youth Action Labs weeded the Grand Avenue rain gardens in south Minneapolis on Thursday. (Glen Stubbe, Star Tribune/The Minnesota Star Tribune)

Along Grand Avenue in south Minneapolis, a street reconstruction project begat 18 blocks of rain gardens — trenches in place of boulevards where native plants grow.

This is the first year they've been in full flourish, and on this side of the summer solstice when all the city's greenery gets a little wild, the gardens have become overgrown for lack of management. Neighbors along Grand have questions and concerns around their long-term upkeep, especially as the city looks to install more across Minneapolis with new street projects.

"It wasn't really clear who was supposed to be taking care of this big weed pit in the front yard," said Claire Blanchette, who was out weeding behind her garage Tuesday. "Am I supposed to be in there? Or is someone coming to do this? I've definitely heard that from people."

In a letter to Grand Avenue residents last week, the city acknowledged neighborhood concerns about the gardens' trash, sediment build-up, weeds and stagnant water. City crews will inspect each garden, mow the vegetation down, remove debris and assess their performance in coming weeks, the letter announced.

The rain gardens capture and treat storm water for pollutants before it flows down the drain toward the Mississippi River. A new ordinance effective January 2022 states that the city must include storm water management infrastructure with each new reconstruction of a street. Rain gardens or tree trenches will be going into the ongoing projects along 37th Avenue NE. and Hennepin Avenue S., for example.

The gardens along Grand were the first of their kind in the city. This summer, they've provided some valuable lessons, said Liz Stout, a city water resources manager and engineer.

"I know that it's not ideal how it looks right now, but we're really excited to to start getting more of these [storm water best management] practices in the ground," she said. "We're not going to be perfect the first time, but I feel like we can take a look at what went wrong, put together a plan to correct it, and then do the project next time even better."

It is not residents' responsibility to climb down into the trenches and pull weeds. A miscommunication with Veit, the contractor who installed the gardens, resulted in the city and contractor each looking to the other to perform regular maintenance, Stout said. As a result, the city will assume upkeep this year.

Other problems that city crews will be assessing include the steepness of some of the slopes leading down from the sidewalk into some of the rain gardens and the blockage of the curb inlets that allow water to flow into the gardens from the street. They'll also examine how small native seedlings of bergamot, purple prairie clover and smooth blue aster are getting smothered by weeds before they get a chance to establish.

Walking down Grand Avenue near 46th Street on Tuesday, Reggie Gandy stopped to look at a rain garden overflowing with sunflowers as tall as him.

"I think it's pretty cool," he said in appreciation. "It's important to think about all the plants and animals that were here before us. As someone who grew up in Minneapolis, I think it's a shame that we don't have nearly as many butterflies as we did when I grew up, so I think if we're trying to be proactive and restore wildlife, these makes sense."

Two days later, the sunflowers had been clipped to the ground.