Q.My lemon tree blooms constantly and produced fruit. The fruit grows to about the size of walnut and then drops off. The tree is 5
years old. Why is this happening and how can I fix it so it bears and keeps fruit? My lemon tree blooms constantly and produced fruit. The fruit grows to about the size of walnut and then drops off. The tree is 5 years old. Why is this happening and how can I fix it so it bears and keeps fruit?

Without knowing more about the growing conditions, soil and water managment for your lemon tree, we can only give you possibilities. Consider water managment, nutrition/fertilizer, and thinning of the numbers of fruit so that the tree water and fertility resources can supply enough for the fruit you have selected to retain.
This article may give you some other tips:
https://www.gardeningknowhow.com/edible/fruits/lemons/lemon-tree-fruit-drop.htm