why are my baby lemons falling off?

Question

Baby lemons are turning yellow and falling off.

Answer 1

A lemon tree goes through three periods of fruit drop during a natural thinning process. During the first phase, 70-80% of the blossoms fall off. In the second phase, which occurs a week or so later, pea-sized fruit falls from the tree. Then, later in spring, golf ball sized fruit drops.

To maximize the number of fruit on your tree, you just need to ensure your tree is getting the care it requires (watering, fertilizing etc.) and that it is insect free. More information on lemon tree fruit drop and lemon tree care can be found here:
https://www.gardeningknowhow.com/edible/fruits/lemons/lemon-tree-fruit-drop.htm