A bioretention basin can be technically sound on paper yet still fall short of expectations if its soils, vegetation, drainage and long-term maintenance are not properly addressed.

That was one of the key lessons from a pilot project presented by Lori Haak, water resources coordinator for the City of Eden Prairie, Minnesota, during StormCon 2026. In her session, “Bioretention Basins and Retired Residents: A Pilot Project,” Haak described how the city used a highly visible residential basin to test approaches for improving bioretention performance while building community support.

Eden Prairie has about 70 city-owned bioretention basins, which typically manage runoff from public rights of way, infrastructure or property. When Haak joined the city in 2022, staff were receiving frequent complaints about a basin in the Stable Path development.

The basin had been designed for infiltration but was holding water for days after rainfall. Residents were concerned about weeds, mosquitoes and the appearance of the site. City staff also were uncertain whether the basin had been constructed and planted according to its plans.

The problem, Haak said, ultimately involved three factors: deficiencies in design and construction, insufficient city oversight and resident expectations.

Expectations start before construction

The third issue became apparent as the city investigated the site.

Development marketing materials depicted several bioretention basins as blue features, creating an expectation among residents that they would function like traditional ponds with permanent or semi-permanent water.

“When you see blue on a drawing like this, you think water,” Haak said.

That created a difficult situation for residents who expected a water feature but instead saw a basin that was neither consistently wet nor dry.

The city decided it needed a successful example that could be shown to developers and residents. Because the Stable Path development was still under construction, staff saw an opportunity to conduct a pilot project while the developer remained involved.

Testing plugs against seed

The city divided the roughly 6,500-square-foot basin into two primary planting approaches.

Staff installed approximately 1,000 native plant plugs in the northern portion, allowing the city to establish a more immediately visible landscape. The southern portion was seeded to compare the establishment of seeded vegetation with plugs.

The approach served two purposes: demonstrating what a mature bioretention basin could look like while also determining whether seed could provide an effective lower-cost alternative to installing plugs throughout the basin.

The city also attempted to address the basin's drainage problems by having the developer regrade portions of the basin. However, the regrading did not resolve the standing-water issue in the area without an underdrain.

Rather than bringing the contractor back for additional work, Haak decided to allow vegetation to establish and determine whether evapotranspiration and plant roots would gradually improve conditions.

Residents became part of the project

Community engagement was a central component of the pilot.

The city worked closely with the homeowners association and identified a resident who became an important liaison between the city and the neighborhood. Haak also attended HOA meetings and held an informational session to explain what residents could expect from the planting project.

That communication was particularly important because the basin was highly visible. The development's mailboxes were located next to it, meaning residents passed the basin regularly.

The city also emphasized what the finished planting would look like rather than simply showing residents technical plans. Haak presented the expected flower colors and seasonal progression to help residents visualize the landscape.

About 10 residents and three city staff members ultimately planted the 1,000 plugs in approximately three hours.

Regular inspections and photographs allowed the city to track changes and respond to residents' questions.

Vegetation takes time

The results reinforced one of the challenges of bioretention projects: native vegetation takes time to establish.

Several years after planting, the basin had become substantially more vegetated and residents no longer saw as much standing water. Haak noted that the basin still holds water in portions, but the condition has improved.

The comparison between plugs and seed was particularly useful. The plug-planted section established more quickly and visibly than the seeded section, while the seeded portion remained somewhat weedier.

Haak said she has become comfortable with the fact that the seeded area will take time to develop.

“I had to come to terms with it,” she said. “But it will develop.”

The city also found that the project provided habitat benefits, with more insects and birds using the basin. Haak said hummingbirds have become a common sight at the site.

Maintenance and construction matter

The pilot exposed several construction and maintenance issues that Eden Prairie plans to address in future projects.

One major problem was that the plans called for the top 6 inches of soil to be amended with 20% compost. After construction, however, the soil did not appear to contain the specified amendment.

Haak said that deficiency likely contributed to slow vegetation establishment, particularly in the basin's drier, sandier areas.

The city also discovered that irrigation serving adjacent areas was contributing additional water to the basin. Working with the HOA to shut off irrigation in that area helped reduce the basin's hydraulic load.

Other ongoing challenges include managing cattails, weeds along basin edges and vegetation growing in riprap.

The project also reinforced the importance of having contractors with specialized experience in native plant installation and maintenance rather than relying solely on general landscaping contractors.

Pilot leads to new standards

The project cost about $8,000, including maintenance through 2025, although the figure did not include city staff time or the developer-funded regrading. The developer also paid for the seed used in the project.

Eden Prairie received an $8,000 cost-share grant from a local watershed district but ultimately spent about $2,500 of that grant.

Haak said the city is using lessons from the pilot to develop new bioretention basin standards.

The city is working on detailed design plates, standardized seed mixes, specifications and a developer-city compliance checklist. Proposed standards include using plugs in basin bottoms and seed elsewhere, as well as plant selections designed to remain within appropriate heights for basin maintenance.

The city also plans to revise its code and establish a project-specific surety mechanism. Haak said native vegetation can take three to five years to establish, creating a need for financial assurances that remain in place long enough to ensure the basin is properly established.

A broader lesson for stormwater programs

Haak's presentation showed that successful bioretention is about more than designing a basin to meet runoff or water-quality requirements.

Eden Prairie's experience suggests that communities need to pay close attention to soil specifications, infiltration testing, underdrain design, plant selection, construction inspection and long-term maintenance. At the same time, residents need to understand from the outset that a bioretention basin is not a traditional pond and that native vegetation will not necessarily look established immediately.

For Eden Prairie, the pilot provided more than a demonstration project. It gave city staff a real-world testing ground for developing standards that can be applied across the city's broader network of bioretention basins – while showing residents what successful stormwater infrastructure can look like.