Disposing of Woody Invasive Plant Material
(You Killed It…Now What?)
On-site vs. off-site disposal
On-site disposal of invasive plants is preferred in most situations because it minimizes the risk of accidental spread of invasive plant seeds to new locations. It is often also the easiest and least expensive method of disposal. By leaving plant materials on site, managers can avoid needing to navigate state and local laws regarding the transport and off-site disposal of invasive plants and can also forgo transportation costs.
Off-site disposal may be necessary when the maintenance of dead plant material on site is not compatible with site goals. The jurisdictions of the Great Lakes region have different laws regarding the transport of invasive plant material and off-site disposal. Here are links to existing jurisdictional resources on invasive plant disposal for Michigan, Minnesota, Ontario, Pennsylvania, and Wisconsin. Note that municipalities may also regulate the disposal of plant waste.
Methods of on-site disposal
Air-drying: Uprooted or cut plants are left on the soil surface with the roots exposed to air to dry them out. They will decompose on site. This is generally only practicable for seedlings/smaller individuals.
Brush piles: Plants are piled up to decompose (similar to air-drying, but can be done with larger plants and branches). Brush piles can serve as shelter for wildlife, though they can also promote increased tick populations.
Leave dead material standing: If left in place, standing dead woody material will decompose and begin to fall down naturally. One advantage of this method in areas of high white-tailed deer density is that the dead material seems to reduce deer browsing on native plants that begin to regenerate after the invasive plant treatment (Cipollini et al. 2009). However, dead woody material, particularly taller trees, poses a safety hazard and may not be suitable for sites with public access.
Chip and mulch: Material can be put through a chipper or ground with a forestry mulcher and then spread on site. If mulch is applied too thickly, it may delay or prevent the regeneration of native plants following treatment. If there is fruit present when the plants are ground up, the mulch should not be to any parts of the site that are unaffected by the invasive species being treated.
Pile and burn: Material can be piled and burned on site. Broad crowned shrubs such as bush honeysuckle may need to be cut into individual limbs or combined with other materials to make a sufficiently dense pile for burning. Burns should be carefully planned and overseen by trained professionals. State or local permits may be required, though the regulations for burning debris piles are generally not as extensive as those related to prescribed burning of natural areas.
Methods of off-site disposal
Composting: Dead plant material, either whole or mulched, is piled and managed to accelerate decomposition. Finished compost is used for a variety of applications and can spread invasive plant seeds if the composting process does not sterilize the seeds. Material from young/immature plants or plants that are treated early in the season (before fruiting) can be composted in any type of setting. Material from mature plants with fruit requires more care and should not be placed in small, residential compost piles. The temperatures of these small piles are unlikely to be high enough to kill invasive plant seed. There is some disagreement over whether the temperatures regularly achieved by large composting facilities are sufficient to kill invasive plant seeds. It likely varies by species, and few studies on seed viability following composting have been done, particularly on woody species. Van Rossum and Renz (2015) found that the temperatures within industrial compost facility piles are sufficient to sterilize common buckthorn (Rhamnus cathartica), particularly when federal guidelines for pathogen reduction are followed.
Landfilling: Where allowed by law, whole or mulched plant material can be bagged and transported to a solid waste landfill. If fruits/seeds are present, double-bagging the material for transport can help reduce the risk of spreading seeds.
Incineration: Where allowed by law, whole or mulched plant material can be bagged and transported to a solid waste incinerator. If fruits/seeds are present, double-bagging the material for transport can help reduce the risk of spreading seeds.
Use as firewood: Dried wood from invasive plants can be used as firewood. Firewood should always be sourced locally to avoid the spread of invasive insects and pathogens.
Photo Credit: Christopher Gogoen, Penn State University – Hazelton