Oranges Don’t Grow Any Larger Than Golf Ball Size
I have recently purchased house with large orange tree out back but oranges don't grow any bigger than golf ball size before falling off. Why would this be?
Certified GKH Gardening Expert
Often, this can be due to a lack of proper fertilization, namely, phosphorus and potassium.
Using citrus fertilizers at least once per year can help. There can be environmental factors, as well. Keep in mind that fruit drop is normal, and should still leave you with a decent crop.
Here are some articles that will help you address the issues, and keep your tree healthy: