I have a 2-3 year old citron (etrog) tree I purchased from 4 Winds in January. Its under a grow light for the winter. In the 2 months that I have had the tree, it had developed about 50 blossoms and a bunch of new leaves and seems to be doing really well. However, the first 5 or so blossoms have dropped off after opening without setting a fruit. Does citron require pollination or is there something else I can do to get the remaining blossoms to leave a fruit behind when they fall off?

My tree is about the same age and is, for the first time, full of flower buds this year. Of the three recently opened flowers one looked normal but the other two much smaller ones were incomplete, lacking a pistil. Those must be the male flowers.

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From The Citrus Industry: The flowers are large, purple-tinged or not, with a variable and often high proportion male (by pistil abortion), and are produced throughout the year.

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From Fruits of Warm Climates: the flower buds are large and white or purplish; the fragrant flowers about 1 1/2 in (4 cm) wide, in short clusters, are mostly perfect but some male because of pistil abortion;

I will hand-pollinate some of the flowers to ensure pollination and leave the rest to nature to see what happens. As an aside, the second quote describes the flowers as being fragrant. There may be a very, very slight fragrance but nothing that can be considered fragrant. Can you detect a smell in your flowers?

eccess watering could cause flower drop to citrus. what i do is water once a week and fertalize with a high ratio of phosphourus 6-18-6 is what i prefere> and that is my personnal experience.

No matter what you do approximately 98 percent of all citrus blooms are discarded by citrus trees. Citrus normally only develop and retain 1-2 percent of the blooms into mature fruit. - Millet

Fertilisation with high phosphorus levels can result in blocking trace elements in the ground, like iron, zinc and manganese, as well as phosphorus will tie calcium and magnesium to nearly insoluble formations, so even if the experience is good, there is no need to do, because most grounds and potting mixtures won't lack any phosphorus, and excess phosphorus won't lead to more flowers or better fruit set.

That phosphorus is adhered to more flowers and larger fruits, is strongly seen a myth!