February 28, 2013
I have heard that you should not plant pampas grass next to a lawn area because it will go to seed and these seeds will start new plants in your lawn.
March 1, 2013
Cortaderia selloana, or Pampas Grass is hardy to zone 5. In looking at one map of "potential planting area", I noticed that it did not include Colorado. If I planted one, I would consider it to be an annual until the plant proved otherwise. There is another ornamentell grass that has the same leaf, but the bloom scape is not as "poofy". That plant is known as Hardy Pampas Grass, the botanical name is Erianthus ravennae, and it is hardy to zone 4.
I've found that Pampas Grass does not seed readily. Clumps of this grass have been in a family member's lawn for 35 years in a Georgia coastal town. They have never had volunteers spring up. The clumps will become quite large with age.
The Miscanthus family is a different story. It is not known as Pampas Grass, but can become invasive if blooms are allowed to mature. It does resenble Pampas Grass somewhat...but clearly different in both heigth, width, color and bloom.