Your local nurseryman could probably be of assistance in diagnosing the problem. It will be time to start feeding acid loving plants such as Camellias, Azaleas, Rhododendrons and Gardenias, when the last buds start to open this Spring and once a month each month thereafter through Fall. Acid loving plants will gratefully respond to an application of a soil supplement to help enrich the acidity of the soil. Your local Nurseryman can help you choose a good product for this. Small trees and shrubs will thrive with an application of a general garden fertilizer.
Larger trees are easy to feed with fertilizer in a stake form.
The stakes contain a slow release fertilizer that give continuous feeding. For rich, green leaves and abundant fruit, it is time to feed all Citrus. Not only will your tree be healthier, but the fruit will be sweeter. No one really has a 'green thumb'. Probably the most important element in gardening is soil preparation.