Ginny, the information that you post is really not enough to answer your post with any assurance. Generally, besides disease or pests, there are four things that could be causing the problem with your friends tree. The tree is not receiving enough energy, the tree is not receiving enough nutrition, the tree is growing in the wrong environment, or the tree is being over or under watered. The only source of energy that is available to a citrus tree is sunlight. At a very minimum, a lemon tree needs 6 hours of direct sunshine per day to function well. More hours would be very beneficial in promoting flowering and fruiting. Second, you say that your friend does fertilize the tree, but you do not say at what rate or how often. However, you do mention that the leaves are a light greenish color. A healthy lemon, receiving the required nutrition, should always have DARK green healthy looking foliage. A 4 year old lemon, planted in the ground needs to be fertilized 3 to 4 times a year. Common fertilizer formulations used on a 4 year old lemon tree are either a 6-6-6, 8-8-8 or a 10-10-10 fertilizer, however other formulations can also be used. A 4 year old tree should receive 1-lb. nitrogen per year divided by the number of applications. In other words, if three application are to be made during the year than the fertilizer should be applied at the rate of 1/3-lb. actual nitrogen with each application. Third, it is never wise to water the tree on a regular schedule. Not knowing the rate of water per hour applied by your friends drip system I cannot say whether the tree is receiving too much water or too little watter. However, the tree should be watered only when it requires more water. Two last points, when your friend planted the tree, she/he should not have added any amendments to the soil, but that was four years ago. Lastly, because the tree is planted in clay soil, the type of rootstock that the tree is grafted upon, is important, especially if the tree is being over watered. Two immediate recommendations that I would offer is to insure that the tree is being fertilized at the required level (I doubt that it is). Water only when it is required. Also, if it was my tree I would also apply a 1 percent foliar spray of either urea, or potassium nitrate, about 1-1/2 months prior to the expected bloom date. Applying the proper amount of fertilizer, and applying the foliar spay should go a long way in solving the trees problem. If we can be of any further assistance, feel free ask. The best to this tree. - Millet (573-)
