I suspect the white patches are powdery mildew and the white leaves is from overwatering.

Powdery mildew looks like a white powder:

mealy bugs are bugs, and they are white and fluffy:

I would give the gardenias good feed of something specific for acid soil loving plants, and hose off the white stuff.

Crystal, I seem to remember you mentioned in a previous post that the gardenias  were dividing 2 driveways.  Is is possible a car being washed in the vicinity is creating this problem?  Car Wash Shampoo?

DEB

Gosh, it looks like someone has shaken a nearly-cleaned painbrush around.  

Interesting.

DEB

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@lloydslights wrote:

Gosh, it looks like someone has shaken a nearly-cleaned painbrush around.  

 

Interesting.

 

DEB

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clever girl, these pots are next to the tap we're using to clean the paint bucket,  brushes etc.

Guess how I know that it can look like that.  

Seen it done hereabouts.

DEB