My lemon tree was given to us about 10 years ago. It was covered with brown scale. I treated it for that and it does produce lemons. The ones now are very large. I believe they are growing on a new shoot that has come up from the roots. This shoot has thorns. The rest of the tree does not. Before this shoot came up, the other part of the tree produced fruit.
Most of the time the leaves look very unhealthy. They are dull and mottled with yellow. I know it needs repotting, and I will do that this spring when I can get it outside. What kind of fertilizer should I be using? It is about 5 feet tall and in maybe a 3-4 gallon pot next to a large window on the south in our garden room. I do prune small dead branches and occasionally live ones for shaping for indoor growing.