|Two of my 3 lemon trees (small in patio pots) produce green, sour fruit, and they drop early.
|Sounds as though you tree is attempting to produce fruit but that it drops before it has a chance to fully ripen. The most common cause of immature fruit drop in lemon trees is due to irregular watering practices. Try keeping the soil evenly moist without keeping it soggy wet. Keeping the soil moisture level consistent will help your tree carry the fruits to maturity and you can enjoy full flavored and fully yellow lemons. Enjoy!