I bought the plant a few years ago at a local plant sale and I was warned that it could be rampant. I wisely planted it in a sunken plastic container. It spreads by underground rhizomes but thankfully the sunken container seems to keep it in check. From time to time, I spot it popping up in other places but it is easily identifiable and easy to pull up.
Plume Poppy is tall and dramatic and can be used as a dramatic focal point in the garden. Just keep an eye on it!