Can you use cedar sawdust for your gardenias?

Yes, under certain circumstances, cedar sawdust can be used for gardenias. Cedar sawdust causes adjustments in soil pH (power of hydrogen) levels over time toward acidic ranges. Gardenias favor the acidic soils that azaleas, camellias and rhododendrons prefer and therefore will appreciate cedar sawdust if the pH is alkaline or neutral but not if the acidic range is correct.