Your site recommends the following: "You can also control Japanese butterbur by planting it in a large container or tub (without drainage holes), then sink the container into the mud, a solution that works well around small ponds or boggy areas of your garden." I know it needs a lot of water, but if the container fills with water in the winter rains or with thorough watering, how will it evaporate without rotting the roots? Will the plant use up the water eventually, even if it continues to rain? (I live in Seattle.) I really want to grow one, but don't have the space or boggy environment. I'm willing to work on it. Please help!
They grow naturally in wet soil, and bog-like conditions. This will pose no issue for the plant, and will prove necessary to keep it from becoming invasive.
Have care when working with invasive species, as when let to reproduce where it isn't wanted, it tends to destroy ecosystems.
Here is an article to help you with the care of the plant: