My washington navel just sprouted a few new flower buds. It already had a large bloom in early summer but none of the fruit held. I thought that it was only supposed to bloom once a year? I remember reading something here about stress causing off-season blooms but this tree appears extremely healthy. Is this an indication of some deficiency?

If you let your tree get too dry, drought can be a stress that induces bloom--it is also important to prevent drought stress during the post bloom period to decrease June drop and retain fruit. Proper watering is often difficult for beginners to master.

It is true that overwatering kills more young citrus trees than anything, but that is often associated with the potting media. A good fast draining media with lots of air spaces can be watered every day without problems, but can also go for at least 4-5 days without watering.

I normally do not water my inground citrus trees unless we are in extreme drought conditions, but during the period from petal drop to the end of June, I watered my inground trees with fruit (except the lemon) and had excellent fruit retention. I did also spray with KNO3.