What happens when there is trouble in paradise and one of your beloved citrus trees shows signs of distress? Why, you just visit UrbanFig to find out the answer, of course! HELP! My lemon tree leaves are turning yellow! There are two primary reasons for lemon tree leaves turning yellow, both of which are pretty easy to deal with. Too much water. Chill out with the watering! You’re overdoing it and the citrus trees don’t like it very much. A good rule of thumb for the most part is to water your citrus trees deeply just once a week.