I've read that some people use their RO waste water for their garden, but I think it's a matter of how bad your local water is. If your waste water comes out at a ppm of 300 or less, you're still doing better than most tap water in CA so I'd say use it. In any case, the most official (seeming) source I could find regarding RO waste water says, "In commercial settings, the potential uses include: pre-rinsing, laundry, toilet and urinal flushing, irrigation, washing hardscapes, make-up water for cooling towers and water cooled condensers, evaporative cooling, decorative fountains, swimming pools, water cooled machinery, vehicle wash, etc." (note: no mention of gardens of landscaping)
RO systems waste roughly 75% of the water they receive, so if you could use a lot of water for the things listed above, I'd go for it. That being said, I don't know if I'd trust my plants (of any kind) to water with higher concentrations of stuff I specifically removed for my plant's health!