Question
Have a eureka lemon tree for about 2 years and have had difficulty keeping leaves on the tree. Growth has been slow and is about 1.5 meters high and about half meter wide. Leaves have looked yellowish. Fruit is small, low yield and does not mature/ripen well. Have used citrus fertilizer and recently blood & bone. Tree looks a little better this year. Thank you.
Joe.

Answer
Hi Joe, Citrus need lots of fertilizer, water and full sun (minimum of 8 hours).  When they drop foliage, it's because they are lacking enough of one of the above.  Use fish emulsion for a fertilizer.  Cut the rate to 1/4th the label rate, but fertilize it every time you water from March to October.  Let it rest in the winter. Give it the sunniest location you can and set it outside when it's in bloom, weather permitting.  You'll get better pollination from insects. You may need to prune it if it's leggy. It will recover quickly from hard pruning.  
Is there a white residue in your saucer or around the drainage hole?
If there is, that's salt, formed by water soluble fertilizers.  If there is, the next time you need to water, set your plant in the bathtub and fill it with warm water to just below the edge of the pot.  Let it sit for a few minutes and then pick it up and let the water drain out.  This will remove most of the salt from the soil.
You won't have salt buildup from fish emulsion.
Jim