Tree roots go where the water and nutients are. I would be very suprised to learn that an Austrailian Willow who's roots activley search deep for water in the arid reaches of the outback turn down the easey pickins of your septic system. If planted downstream (hill) or around the leach field, it may not be as much of a problem. Just my opinion, so you may want to check with the ASU extension office, they may be able to guide you on this.

jkochan, thanks for your opinion. I'm thinking it might not be safe to plant it. It sure would be expensive lesson if it invaded the septic tank. This leaves me confused as to what I can plant. How do I get in touch with ASU extension office?

Just about any tree and a septic system is a problem waiting to happen. You might want to consider some raised beds for the area and some flowering shrubs? Heres a link to the ASU home page.

Here is a link that might be useful: ASU Extension Office Home Page

Just a reminder that it's the U of A Extension Office. This is the outreach branch of the College of Agriculture and Life Sciences (CALS) which is based in Tuscon. There are Extension offices in every county in the state and they are charged with bringing the university to the people of Arizona.

If you call 602-470-8086 x 301 you'll reach the Master Gardener hotline where you can leave a message. A MG will call you back. OR, you can post your question to the arid_gardener list serve. This is hosted by the U of A and can be accessed from the "Ask a Question" link on the Maricopa County Extension office listed in jochan's message above.

I have this tree and one thing I have to say about it is that it seems to take more water than some of the other drought tolerant trees. It looks "wilted" and does not thrive with the same water as my Mesquites,Palo Brea and some various Acacia trees.

Australian Willow is Acacia salicina which is not a true willow but does have graceful, drooping branches. This tree is a fast grower on drip irrigation and reaches heights of 30 feet witha 15 foot spread.

It is considered low water use but I'm not sure if it would survive on rainfall alone in your area.

Here is a link that might be useful: Australian Willow

Forgot to mention that Australian Willow could also be Geijera parviflora. Common names can be pretty confusing.