Answer: Gardenias like acidic soil so I can understand why your friend may have used vinegar, an acidifying agent, to water her gardenia. However, I don't know what a safe ratio of vinegar to water might be. It would be better to use a commercially prepared fertilizer specially formulated for acid-loving plants. If you can't find one specifically for gardenias, one formulated for camellias and azaleas will work. Gardenias should be fed every 3-4 months during active growth (spring, summer and fall) in amounts as suggested on the fertilizer label. Best wishes with your gardenia!
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