sentences:  For this reason, it is advisable not to water gardenias with very hard water.When having to water with hard water, it is possible to add some vinegar or lemon juice to it before doing so, this will lower the pH of the water, or use an effective pH modifier, like phosphoric or nitric acid.Iron chelate can be added to the soil to lower the pH, but care must be taken since an overdose can kill the plant, as with any other inorganic soil amendment.