Help with Gardenia

I need help with my Gardenia.

It's six years old, I grew it from a cutting. At first it was planted in a pot, and it thrived there to the point where it covered that whole area pictured with its branches. Then a few years ago it started losing all its leaves. We figured it needed to be planted in the ground. When we removed it from the pot the soil was full of little black ants. We planted it on the location where the pot had always been, and it looked like it died, until these leaves started emerging two years ago. But it's always had yellowish leaves, and flower and leaf buds often fall before they can mature. It's never really been the same since.

This is in the Philippines, which means it gets enough sunlight, so I don't think lighting is the problem, and it's regularly watered. There are some tips which suffer aphids (pictured), but they only affect a few leaf buds and that doesn't explain why new branches don't emerge.

Can anybody help me? This particular plant has lots of sentimental value for me.

Hey LHS!
I think you have a few problems with this poor child: Major is lack of iron in the diet. Gardenias need plant food high in iron and acids to thrive. BUT!!! The other problem is you DO have aphids, and a lot of them. If you popped it out of the pot to find black ants, that means the ants are harvesting "honeydew" from the aphids. "Honeydew" is just a nice word for "aphid poop". It's sweet (go figure!) and these ants actually protect the aphids from other predators (theirs is a small world, but fierce) and collect their bounty of honeydew. Meanwhile. the aphids are sucking the life out of your gardenia.
So... if you want to save this guy, you're going to have to treat for aphids. Mild soap diluted in a hose end sprayer will be fine. You don't have to buy special soaps they charge a bundle for in garden centers. Liquid hand soap or dishsoap will work fine. I tend to fill the hoseend sprayer with soap and dial the dilution WAY up so I can see suds forming on the plant. Then blast away. The soap will also go into the soil and (hopefully) annoy the ants so much that they leave.
Now, about that acid based food: feeding a plant has RARELY caused a turnaround in a plant this damaged. I would start over with a fresh, healthy plant. (Sorry. I know it's your baby.) But if you want to grow gardenias, you need that iron/acidic food anyway to keep them healthy.
So try to save this guy by treating the aphid/ant issue first and then feeding with a food high in acid. NEVER feed a dry plant, by the way. NEVER. If the soil is dry, water first. Always make sure the roots are moist for at least a day or so before feeding. The food is a chemical and will damage the fine roots that take up nutrients, and you don't want to do that.
Good luck!

This message was edited Apr 12, 2018 10:43 PM

Thank you very much for this! Yes I suspect it's something to do with the acidity of the soil. I haven't tested the soil's PH yet, but I was thinking of doing just that. I'm thinking of watering it with vinegar diluted in water.

As to the aphids, yes I'll be using dishwashing liquid to brush them off. I don't need to worry about the ants anymore, they're no longer there.

I was fearing someone would say it's helpless, but I'll try saving this anyway. But just in case I'm thinking of marcotting a few of its mature and healthier branches. Do you think marcotting would work?