how do I control spread of leaf yellowing?

Question

Had one gardenia plant lose all leaves. Second one showing same condition. I treated both plants with iron chelate 10%.

Answer 1

You are not alone with your gardenia having yellow leaves. Gardenias can be fussy.
There are a few reasons for this, so I'm including a link to a great article to help you pinpoint the reason.

https://www.gardeningknowhow.com/edible/helping-a-gardenia-bush-with-yellow-leaves.htm