Fireweed is an iconic plant of the Northwest. It needs disturbance, and is often one of the first colonizers of a heavily burned site. This ability to deal with disturbance means it also does well in human-altered areas, aka your garden. Fireweed spreads quickly in the absence of competition. I recommend planting it with canada goldenrod (another somewhat aggressive early colonizer) and letting the two duke it out, but any closely spaced established plantings will prevent spreading. Fireweed is tall; plant it along fences and walls for best effect.