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Planning commission recommends denial of proposal to allow rock mulch in city landscape planters
Summary
After extended discussion about aesthetics, weeds, heat, enforcement and lack of specification for rock type or depth, the commission voted to recommend denial of a proposed citywide text amendment that would permit rock mulch in required landscape planters. The denial (recommended Alternative 2) will be forwarded to city council; the transcript records a 5–1 vote.
City staff presented a proposed citywide zoning text amendment, requested by the ISU Research Park, to allow rock mulch as an alternative to organic mulch in required landscape planters. Staff explained the city’s 2017 decision to keep an organic‑mulch requirement and said consultant work at that time emphasized organic soil content as the primary driver of plant vitality; staff proposed language intended to confine rock to under‑planting areas while maintaining a requirement for ground‑cover plants.
Commissioners raised a range of concerns. Several members said rock mulch can increase weed problems if not installed to sufficient depth, can become very hot in parking‑lot planters, and can be used as a convenience substitute for required planting if enforcement is complaint‑driven rather than proactive. Commissioners also noted staff had not specified rock type, color or depth in the proposed language and worried that the amendment’s citywide scope could lead to widespread use contrary to community aesthetics. Staff said they could investigate specifications such as rock depth or type if the commission recommended modifications.
After discussion, Commissioner 2 moved to recommend denial of the requested zoning ordinance changes (Alternative 2) and Commissioner 9 seconded. The commission’s recommendation to deny was approved and staff will forward the commission’s denial recommendation to city council; the record indicates a 5–1 vote in favor of denial.
The recommendation is advisory; council could still consider rock‑mulch allowances or direct staff to return with more specific language addressing rock type, depth and limits on area.
