There are English tours of the Ethnobotanical Garden on Tuesdays, Thursdays, and Saturdays at 11 am. Tour lasts 2 hours. Cost is 100 pesos per person as of July 2009. The only way to see the Ethnobotanical Gardens, except out of the windows of the Santo Domingo cultural museum (west by the front of the church) is to take a tour. It's very much worth the trip. You learn a whole lot about the region and its botanical diversity which is far more diverse than you are likely to guess. Tour in Spanish  is on Monday and Saturday, at 10,12, and 5 pm.  Cost is 50 pesos and is one hour long. Entrance at Reforma and Constitucion streets, www.jardinoaxaca.org , 951 516 5325 ,  jetnobot@prodigy.net..mx

Honestly, one of the most interesting botanical gardens you will ever go to, and though underfunded, you are personally contributing to the upkeep and development of every plant and tree you see and to those who care for them.