Question
I am growing a grapefruit tree from a seed in a pot.  It started quite well but I recently transplanted it to a larger pot.  I noticed that the top layer of the soil gets a white dusty coating on it after it has been watered.  Is this mold/mildew? Am I overwatering?

The plant is still small (about 6 leaves).  I am not really expecting to grow a treee but it was fun for my kids to see a plant grow from a seed that came out of a fruit they were eating.  

Since repotting, several new leaves have grown but one new one recently fell off.  Another is starting to look a little pale and is starting to curl.

Any help you can offer would be greatly appreciated.

Thanks!
  - Kurt

Answer
Kurt,
It is either salt deposits from hard water or mold.  If it is crystaline and your water is hard or salty use cleaner water.  If it is powdery and under close inspection looks like it has filiments or micro strands it is a mold from overwatering. You could try a fungicide or a cautious home remedy.  Put 4-5 drops of chlorox in 10-12 oz water in hand spray bottle and be only to mist the mildew but do not wet the soil. Citrus don't do well in subdued light and leaves will fall.  It needs full sun to do well.  Make sure there is good drainage and water very well only when top 2 inches are quite dry.  Of course depending on size and type of soil media but you shouldn't water more than once or maybe twice a week and then only about about I say 2 oz water per inch diameter of pot.  Y
Happy gardening
Bryan