Because one side of the tree had sparse foliage it could indicate girdling roots. If the roots were potbound when purchased, they will wrap in a spiral around the original root ball. As the trunk expands, it contacts the spiraling roots and cannot grow more. This can stress one side of the tree and cause leaf and fruit drop. The girdling root has to be carefully dug out and cut off.
Citrus also suffer from root rot in a lawn setting with regular irrigation .
They eventually die. A. Yes, leaf drop is normal for March. Vigorous new growth and flowers also should be appearing now. If the tree has lost more than three quarters of its leaves at one time, I would suspect root rot and excess water. Q. We live on a canal that has a seawall in the backyard.