What are the different signs of overwatering or under watering a young Meyer lemon tree?

Hi David, lemons indicate they have too little water by the leaves going yellow, then falling off the plant and starting to shrivel. The plants literally defoliate. Too much water triggers the plants to defoliate as well, however the leaves do not normally fade in colour and the tips of the stems will go black.

The soil should be moist but not water logged. Lemons can go for long periods without water.