Is composting invasive plants a good idea?

Now is the time of year when many of us are removing unwanted invasive species or mulching to prevent new weeds from establishing in our yards. You may use your local municipal yard waste mulch piles or a home compost pile to help with this work. However, while using composting and mulching options for managing unwanted plants, it is critical to understand the potential impacts of composting invasive species, of using mulch from local brush dumps, and your local government’s policies, in order to reduce the spread of invasive plants via composting.  

In general, the best time to dispose of invasive plants is before plants flower and produce seed. After the fruits or seeds develop, make sure to minimize movement of the plants to prevent unnecessary dispersal. If possible, leave plants on site.  This will reduce the potential to spread invasive plants to un-invaded areas. If you choose to dispose of your plants at a municipal site, and your municipality allows it, it is helpful to understand the biology of the invasive you are composting. 

A recent study by Joe Van Rossum at the University of Wisconsin Stevens Point (unpublished) looks at assessing the ability of municipal compost piles to kill active seeds. Results of this study suggest that up to 99% of garlic mustard and common buckthorn seeds are killed at the temperatures reached by large scale composting. Plants such as garlic mustard, dame’s rocket, and common teasel spread by seed. Woody invasives like common buckthorn, multiflora rose, and autumn olive that lack seeds can be safely chipped.  These should be pulled and left with roots exposed until they have dried out. Once they are fully dead and dried they can be composted or left on site.  If there is any seed material it should be left on site or be placed in a large scale composting system and not simply a brush pile.

Contrary to woody plants and seed material, some species should never be composted because they have rhizomes or other parts that may survive in the compost and spread to new locations when the compost is distributed. Herbaceous plants that spread by rhizomes (horizontal, underground stems) such as Japanese knotweed (pictured at right), purple loosestrife, and reed canary grass should never be composted. The best options for disposing of these plants is landfilling in a clear, plastic bag labeled “invasive species” or burning in accordance with all federal, state, and local laws and ordinances.

If you plan to use your local brush dump or home composting site for your yard waste, it’s important to know the state and local laws regarding invasive species disposal.  It is illegal to dispose of yard waste in landfills in Wisconsin.  However, there is an exception for invasive species.  Wisconsin Administrative Code NR 40 allows invasive species yard waste that is bagged and properly labeled to be disposed of in a landfill.  Along with the State Statues some cities and towns have local policies to help prevent invasive species spread via yard waste disposal sites. You can learn more about what to do with your yard waste and invasive species and your municipality’s policy regarding public brush and composting sites by visiting their website. With a little bit of knowledge you can help clear your land and lawn of invasive species while helping to avoid their spread to distant sites.  Happy weeding!

For additional information on the proper disposal of invasive plants visit:

Compost with Care: How to dispose of invasive plants responsibly