A serious pest where it establishes. The USDA lists it as not having yet been naturalized in Pennsylvania, but it is rampant in New Jersey and I have been watching it take hold around planted specimens, particularly these under an onramp to I-95 near Morris St., seeded from where they were planted along the other side of the highway. There are approximately fifty volunteered clumps along the onramp. It will likely soon completely dominate the whole strip.

These are the original plantings. The arrow marks where the new colony is becoming established.

The only other sprouting of Pampas Grass that I am aware of is in the Broad and South Garden, where it was planted by Allison Weiss. The full-sized plant above is a volunteer but the plants behind it were intentional. This invasive grass should not be planted in Pennsylvania.