Why are the leaves falling off my lemon tree?

Hi Mervyn, 

Citrus are evergreen but do drop leaves, usually when they are stressed - this could include being too cold, too hot, the result of too much fertiliser, or not enough fertiliser, if there’s frost, or if they are too wet. We would suggest regular doses of Tui Organic Seaweed Plant Tonic every seven days until the tree starts bursting into leaf.

Feed regularly in spring and summer. Don't feed it in winter as the tree isn't actively growing. Try adding sheep pellets to nourish the soil and mulch around the tree so it doesn't dry out in summer. If it is in a pot and become pot bound it might need re-potting.