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Interim Invasive Plant Policy

Adopted July 2022, pending incorporation into an updated Collection Policy

Invasive plants and animals are threatening our Michigan habitats. We have procured plants from all over the world for our collections. As a public garden, we are conscientious of how plants in our collection might affect the local environment. Because the Garden floods occasionally, and river water can easily disperse seeds and propagules downstream, we must be cautious about potential spread of plants from our collection. We are committed to removing any plants from our Garden that are harmful to the natural or created landscape around us.


  1. Species on the Michigan Prohibited and Restricted Weeds list will not be included in the Garden collection.
  2. We will not add to the collection any plants listed on the Michigan Watch List for invasive plants
  3. All plants in our collection will be monitored for invasiveness based on the criteria below and will be removed if they are believed to be a threat to the local environment. Species on the Michigan Watch List included in the collection will be evaluated every year.
  4. In an effort to reduce the risk that the Garden might introduce new (and potentially more invasive) genotypes of weeds already growing in Michigan, we will not import and grow accessions of Michigan weeds from outside the state.
  5. Exceptions to the above restrictions can be considered for inclusion in the collection if living plants of the species are required to fulfill a critical education or research goal and if the horticultural staff confirms that the resources are in place to grow the plant in a way that prevents its spread.
  6. In acknowledgment of the fact that removal of invasive species negatively impacts the Garden’s ability to educate the public about these species, efforts should be made to mitigate that lost opportunity by identifying opportunities to educate the public about specific invasive species and to share our findings about the invasiveness of non-listed, non-target plants with the appropriate agencies and organizations.


Plants will be declared invasive in the Garden and removed if they meet any of the following criteria:

  • The plant is found in three or more beds or other locations more than 15 feet from the place where it was intentionally planted.
  • The plant spreads by rhizome or runner into adjacent locations in the same bed or adjacent turf and requires disruptive removal more than once during the growing season. Disruptive removal refers to situations in which removing the spreading plant creates considerable damage to adjacent plants in the collection or unsightly damage to the turf.
  • The plant spreads by any means so intensively within a bed that it routinely threatens the health of other adjacent plants in the collection and requires unsupportable management practices such as unsustainable levels of staff time or excessive use of chemicals.



To oversee these policies the Director will assign the role of Invasive Plant Species Coordinator (IPSC) to a staff member. The responsibilities of this role include researching effective invasive species removal strategies (best practices) that are locally effective; oversight of removal of invasive species in the Garden; working with Landscape Services to help them identify invasive species concerns and advise them on removal strategies; interfacing and collaborating with local, state and regional invasive species organizations; building productive relationships with University partners focused on invasive species research, teaching, and outreach; and outreach to the public about invasive species, both as part of Garden programs and at other local and regional events. Documentation of our efforts removing invasive species should be promoted in outreach and social media to raise awareness.

Step 1: Any staff member who is concerned about the potential for invasiveness of a plant species, observes spread of a potentially invasive plant, or receives a request to review a plant species by an outside party, can recommend a review of a species to the IPSC. The IPSC should conduct or oversee a review of the species. The review should include documenting the spread of the species through direct observations and/or via reporting from the horticultural staff with regards to the criteria above.

Step 2: Once this information is compiled into a brief written review, it should be shared with the Collections Manager and a designated member of the horticultural staff. These three people will form a review panel and will make a preliminary recommendation about whether the species should be kept in the collection (unless a later request is made), whether it should be removed from the collection, or whether it should be reviewed the following year before any decision is made. In rare cases (#5 above), a recommendation could be made to keep a species found to be invasive in the collection or import genotypes from outside the state. In those cases, the recommendation from the panel should include a set of management practices that have been agreed upon by the horticultural staff that will keep the species in check. This species should be added to a list of plants to be reviewed every year to confirm that the management practices are sufficient to keep the species from spreading.

Step 3: The written review together with the preliminary recommendation of the panel should be shared with the Garden staff and everyone should have the opportunity to respond to the recommendation. The panel should consider the responses, adjust the recommendation if warranted, and make a final recommendation to the Director who will make a final decision in each case.