Lemon trees (Citrus limon) relish a sunny location in a fertile, well-draining soil in regions where frosts and freezes don't occur. As long as the roots, trunk or one branch remains alive on the tree, it may still resprout and continue to grow.
A living lemon tree will display oval evergreen leaves year round. Living branches with sap flowing within will flex gently and do not snap. Scratching into the bark on branches or the trunk to 1/16-inch deep to 1/8-inch deep reveals a green, damp layer on lemon trees that are still alive. Dead bark shrinks tightly and cracks.
Causes of Death
Extended temperatures below -3.89 degrees Celsius cause leaf drop, branch dieback and even trunk and root death. Excessively dry soil leads to plant demise as can any number of insects or fungal diseases, especially when the soil is too wet or slow-drained.
Symptoms of a failing lemon tree include leaf drop, abortion of flowers and shrivelling of fruits. While some branch dieback is common on older trees, large branch or canopy sections quickly defoliating and dying suggests a larger cultural or disease problem. After winter cold, wait six months until after the midsummer to pronounce the tree fully dead if no regrowth appears.