was bought a small lemon tree a few xmas' ago and with my tiny old house it did fine on a sunny southwest window. It never went outside but still flowered and grew a number of small lemons. looked very healthy, happy, putting on lots of new growth but unfortunately it didn't take to the move in October year before last as i had no sunny window that was was cool in winter and so it died. Could have been a combination of overwatering too, but believe it was more down to the heat of the house in winter and lack of sun as i managed to keep it alive previous winter in the kitchen which was always cold due to the pathetic excuse for a radiator.

I'd agree with what people have said above only water when soil dries out and give good drainage, but make sure its cool in winter. However i used two different feeds, one for summer and one for winter, as thats what this book recommended. Its called 'success with citrus', think you can get it through a company called Orange groves uk, should have the number somewhere if u want, so let me know