3 year old Meyer lemon tree still dropping all fruit.
Thanks for your question.
Due to the limited information provided regarding your situation, it is not possible to point to any one particular cause for this issue of your 3 year old Meyer lemon failing to set fruit. The good news is that you should not give up hope, and that your tree can and will bear fruit still.
It is likely that your tree is not receiving proper care. Citrus trees are heavy nitrogen feeders, and heavy bloomers. If the trees do not have access to enough nitrogen during and after bloom, it may fail to set fruit.
Keep in mind that granular fertilizers require a few weeks to really start having an effect on the tree. So, fertilizing while the tree is in bloom is too late. Citrus trees need ample fertilizer at least 2-3 weeks before they begin to bloom so that these nutrients can be made available to the tree and willl start to be picked up by the tree before and while it is developing fruit.
A three year old citrus tree should be receiving at least 1/2 pound of actual nitrogen per year. If using a fertilizer like 13-13-13, this means applying 3.5-4.0 pounds of fertilizer per year to the tree in order to provide the 1/2 pound of actual Nitrogen (13-13-13 is 13% actual N by weight, 3.5*.13 = 0.45lbs N). Likewise, you could use a product like 21-0-0, where you would only need 2.0-2.5 pounds of fertilizer to supply 0.5lbs of actual N.
Most soils typically have enough phosphorus, potassium, and micronutrients to keep the citrus healthy, but are lacking in nitrogen, so this is the most important element for citrus. However, the use of a 13-13-13 product or something like a 15-5-10 is also good.
Divide your fertilizer into three applications throughout the year. Make the first application before or just at budbreak in early spring (maybe late February for you), the second application in early May, and the 3rd application in late June. Split the total amount of fertilizer needed for the year into 3 equal applications (if 3 pounds is needed over the year, make three applications of 1 pound).
Avoid letting the soil get too dry around your citrus tree. Drought stress during the growing season can slow the growth of the plant and may cause fruit to shed.
Do not prune heavily, as a citrus tree needs all of its leaves to photosynthesize and create energy for itself. Likewise, citrus should be planted in full sun locations.
It is generally recommended to remove blooms and fruit on trees less than 2 years old so that the tree grows to a large enough size and becomes established enough to bear good fruit. Do not give up hope. Your tree is young and is just coming into healthy bearing age. Apply ample fertilizer at the right time and keep the soil moist and your tree should provide many bountiful harvests.
Keep in mind that as your tree gets older and bigger, it will need more fertilizer.
Years 4-6, increase your fertilizer application to supply about 0.75lbs of N per year. Years, 7-8, increase to supply about 0.9lbs of N per year. For trees 9+ years old, supply 1.5lbs of N per year.
Let me know if you have further questions.