My bush has white sticky stuff coming from its branches, and the leaves are turning yellow.
Gardenia Bush (White, Sticky, Seeping)
Certified GKH Gardening Expert
The following article should be of some help to you: https://www.gardeningknowhow.com/ornamental/flowers/gardenia/helping-a-gardenia-bush-with-yellow-leaves.htm
Gardenias are vulnerable to various insects including: Aphids, Mealy bugs, Scales, SpiderMites, Thrips, and Whiteflies. The first three secrete a sticky substance known as honeydew. If it’s cotton-like in appearance, then most likely your problemis due to mealy bugs. Here is a link you may find helpful in treating this pest problem: https://www.gardeningknowhow.com/plant-problems/pests/mealybugs-white-residue-on-plants-leaves.htm
Regardless of the pest, neem oil is an effective treatment as well. This article has more info: https://www.gardeningknowhow.com/plant-problems/pests/pesticides/neem-oil-uses.htm