grapefruit tree

Question

Fruit set this spring but by Aug. fruit is still only marble size. I put compost around tree and water every week here in southern Arizona. What do I need to be doing?

Answer 1

It sounds like you are taking the right steps, but it's possible that the tree needs even more water (not greater frequency, but more water each time). Alternatively, you could try providing more phosphorus (which helps fruit growth) in the form of bone meal or another high-phosphorus fertilizer.

https://www.gardeningknowhow.com/edible/fruits/grapefruit/growing-grapefruit.htm