Hi, 

It does look like it is a bit chlorotic or low in iron to keep the leaves green. It takes a little while for the plant to receive the soil adjustments, so it could still be fine. Have you taken a soil sample? It may be a good idea to see what the nutrient levels and pH or acidity levels are. If the pH isn't in an optimal range for the plant, it will have a hard time taking up nutrients. 

Gardenias prefer more acidic soil. It could be that the soil is too basic or the pH is too high near the foundation and bricks? Is there a roof overhang and it isn't getting sufficient water? Is it in full sun? They prefer some afternoon shade. 

You can read more about soil testing and choose a laboratory on our reference page. It can take a few weeks to get the results, but we can help interpret them once you receive them. In the meantime, don't add more fertilizer or soil amendments as it could stress the plant further, and just check the soil about once a week for water  and irrigate as needed. 

Let us know if you have further questions. 

Emily