Invasive species are certainly a concern with a lot of things: just look at how Kudzu has taken over so much stuff in the American southeast.<p>However, cacti I would think would be unproblematic, especially saguaros.  Saguaro cacti are huge when mature, but it takes over a century to reach that size.  They&#x27;re very slow-growing.  They&#x27;re <i>not</i> going to overtake any land on their own unless you intentionally ignore it for a few centuries.  Moreover, they only do well in the Sonoran desert where the climate is right for them, and there&#x27;s no competition or predators.  They wouldn&#x27;t last anywhere where anything could eat them (not likely with the spines of course), or where the weather killed them off (they probably can&#x27;t handle freezing temperatures very much).  They can&#x27;t even handle too much wind: their root systems are very shallow, and they tend to fall down in storms when they&#x27;re old.  Young and middle-aged ones that are transplanted are normally propped up with 2x4 lumber for a while to let their roots grow more; it&#x27;s an extremely common sight in Arizona in places with new development where they transplanted some cacti in for landscaping.