Proper Disposal of Invasive Plants
Knowing how a particular plant reproduces indicates its method of spread and helps determine the appropriate disposal method. Most are spread by seed and are dispersed by wind, water, animals, or people. Some reproduce by vegetative means from pieces of stems or roots forming new plants. Others spread through both seed and vegetative means. Some plants continue to grow, flower and set seed even after pulling or cutting. Seeds can remain viable in the ground for many years. If the plant has flowers or seeds, place the flowers and seeds in a heavy plastic bag “head first” at the weeding site and transport to the disposal site.
Is burning an effective disposal option?
Burning does not tend to be the magical answer that many landowners are hoping for. In fact, invasive plants with airborne seeds may disperse by the hot air created by the fire. Also, there are many burning restrictions that must be adhered to and its probably best to avoid putting more smoke into the atmosphere.
Bagging, tarping and drying
Bagging (also known as solarization) is a suitable technique for plants with softer tissue. Use heavy black or clear plastic bags (contractor grade), making sure that no parts of the plants poke through. Allow the bags to sit in the sun for several weeks and on dark pavement for the best effect. Tarping and drying is another method that can be effective if done correctly. Plant material should be piled on a sheet of plastic and covered with a tarp, fastening the tarp to the ground and monitoring it for escapes. Let the material dry for several weeks, or until it is clearly nonviable.
On some properties, burying plant material may be an option. This is risky, but can be done with watchful diligence. Check with me before trying this technique, as some species require fairly deep burial. Japanese knotweed, for example, must be buried at depths of 2 metres. Other species, such as puncturevine, only require burial of 15-20 cm.
Japanese knotweed is not a
suitable candidate for
composting as it must be buried
at depths of at least 2 meters
Probably the most commonly used disposal technique is composting. However, composting of invasive plants must be done with extreme care. These aggressive plants can take root in compost. Species such as knotweed, morning glory (bindweed), sheep sorrel, ivy, several kinds of grasses, and many other plants can re-sprout from their roots or stems in the compost pile. Do not compost any invasives unless you know there is no viable (living) plant material left. Use one of the above techniques to render the plants nonviable before composting.Keep this in mind when you dispose of the annual plants in your planters and hanging baskets. Improper disposal of garden waste can result in undesirable ornamental plants moving into natural areas or parks adjacent to your property.
Closely examine plants before composting and avoid composting seeds. The majority of composting practices and processes often do not reach and maintain the temperatures needed to assure the destruction of all viable seeds; this is particularly the case with backyard composts. A study by Agriculture Canada indicated that some species of weeds, including wild mustard and stork’s-bill, were killed early in the composting process, with the temperature held at just 39 degrees Celsius for a week – a fairly low temperature for compost piles, which should be generating temperatures of 55-60 degrees Celsius. However, a graduate student in Washington recently showed that temperatures in excess of 100 degrees Celsius were required to effectively destroy the seeds of Dalmatian toadflax.
Disposal at the Landfill
Any mature invasive plants with seeds should be carefully bagged or loaded into the back of a truck (covered with a tarp or canopy), and disposed of at the landfill. Be sure to inform the landfill operator that you have invasive plants and not simply yard waste, to ensure that your weeds are disposed of in the proper location. And if you have curbside pick up, do not include any invasive plants with your yard waste. In the RDOS, the tipping fees are waived for disposal of invasive plants.