OK, hypothetical situation here. Property owner 1 has a bed that sits right on the property line, and within that bed is creeping euonymus fortunei or English Ivy or some other spreading plant. Property owner 2 has turfgrass that abuts #1s planting and doesn't want English Ivy, etc, on their property. Is it Property owner #1s responsibility to keep the creeping plants off of Property owner #2s property or vice versa.? When does a "plants natural habit of growing and multiplying cross the line(literally and figuratively) when intentionally planted by humans.?" The next level would be "What about plants that spread by seeds?" Those damn whirlybird seeds from Silver Maples that get everywhere, or a classified noxious weed like Lythrum or Asian Honeysuckle. Throw out some thoughts.