Wish I saw this sooner! (well, I guess it was after the fact...) Here's what you just missed this weekend for Make A Difference Day:
Growing Together Garden is located on Glendale Ave at 2nd St. (SWC) just east of Central Ave. They usually have weekend volunteer work days. You can sign-up on the website to receive email updates. http://growingtogetherphx.org/
In addition to your "hands on" gardening experience, I suggest you explore The University of Arizona Cooperative Extension- Maricopa County. There is a wealth of information available, including several books available that deal specifically with the challenges of gardening in a desert environment. If you go to www.maricopamastergardener.com/pubs.htm , you will find many pamphlets and short publications on desert horticulture issues. You may even have an interest at some point to enroll in the Extension's Master Gardener program. Good luck!