Disposal methods for selected invasive plant species used as ornamental garden plants

Invasive alien plant species are frequently grown as ornamental plants in gardens. Until recently, in Slovenia, there were neither specific collection centres for a safe disposal of invasive plant species, nor any legislation that defined procedures for their removal and disposal. We investigated in two experiments how to dispose of pieces of selected invasive plant species, with the aim to prevent their survival and further dispersion. In the first experiment, we chose eight species that are known for spreading by either growing from pieces of cut stem (Cornus sericea, Parthenocissus quinquefolia, Buddleja davidii) or through subterranean rhizomes and tubers (Solidago canadensis, Solidago gigantea, Rudbeckia laciniata, Helianthus tuberosus, Symphyotrichum novae-angliae). The plant fragments were exposed to three different storage treatments: drying, composting on an open compost heap, and storage in black bin liners, all of which can be used in the home garden. After 5 months of storage, the materials were planted in box planters, and their development was monitored. Drying and composting was highly efficient for disposal, as the conditions destroyed the majority of the plant material. However, storage in a bin liner was inefficient because it did not kill any of the plant species tested, and did not delay their growth of new roots. In the second experiment we investigated selected woody invasive plants (Cornus sericea, Parthenocissus quinquefolia, Buddleja davidii, Acer negundo, Forsythia x intermedia) to determine whether their branch fragments can sprout new roots, and whether shredding of their branches represents an efficient dispersal pathway. These dried fragments did not grow roots under any circumstances, while freshly shredded fragments rooted in some cases. Therefore, the use of mulch that has not been treated properly might allow dispersal of woody invasive plants. We can conclude that not all recommended treatments for invasive plant disposal are equally successful to prohibit plant survival and further spread.