Consiistent watering, a good citrus fertilizer applied per label directions and lots of sun makes the sweetest citrus.

I dont believe there is much that we can do to increase the amount of sugars other than allowing the tree to do its thing. I believe that naturally the sugar content increases as the fruit ripens and for some the cooler weather in fall also brings up the sugars. Being sure the tree is in the best health will always maximize it and the the fruits potential.

Mike

I agree with the responses so far. A healthy tree will give you the best quality fruit. Also, mandarins in particular my take many years to yield maximum fruit quality, so you must have patience.

Some people have had anecdotal success increasing the perceived "sweetness" of citrus fruit by giving the trees epsom salts. I am not sure of the mechanism, and I haven't personally tried this, but there are reports of this working out there. Good luck.

-Brett