Hi. I have a Ficus Microcarpa and leaves turn yellow, I cut the yellow leaves off, and other leaves then turn yellow, and again I cut them off.  If I keep doing this, there will be no more green leaves to photosynthesize.  The new leaves are yellowish in color--if the leaves were green, I don't think this would be a problem.  I think the Ficus is supposed to lose leaves over time and not all at once--but the new leaves are yellow, which I think are damaged.  I read that yellowing is a sign that there is a nutrient deficiency or watering problem.  To water and fertilize, I mix SuperThrive Bonsai Pro--which has a ratio of 7:9:5 with water.  I also spray the leaves with water a couple of times a day.  So, I was wondering if this is a cause for concern, and the cause and remedy for this situation, if there is a problem.  Thanks.

Ficus do shed more leafs and produce less new in authum and winter if kept in livingroom conditions in temperate regions. If you are in the southern hemisphere going into spring now or in a tropical climate, obviously that answer do not apply.

The new growth on your tree is normal light green. I see no issue with them and they will green up by time. If you are in a nortern temperate region it will take time. Maybe even until spring depending on how long north you are. If you are getting into winter, the authum equinox is passed now and you should stop or reduce the fertilizer depending on latitude.

You can reduce leaf drop in winter with one or more of the following actions. Reduce temperature to 10c. Increase humidity by putting it into a terrarium, grow tent or greenhouse. Add articicial light.

As you can see location, growing conditions and climate plays a role. Next time asking a question, please give that information as it will be much easier to answer without all ifs.

Anyway, to answer your main question. Is there any reason for concern. There are never any reason for concern in bonsai. Concern never helps the tree and stresses the owner. Quite often it leads to drastic actions that makes things worse.

Hi--thanks for the answer.  Yes, I live in Missouri and am moving into winter; so you are saying to disregard the makers of SuperThrive Bonsai Pro instructions and mix water and the fertilizer different from what they state--one teaspoon for half-gallon of water?  After spring arrives, I can return to the makers instructions?  Thanks.

I do not fertilize any plants in winter. Cactus enthusiasts do not fertilize in winter, orchid growers do not fertilize in winter, farmers do not fertilize in winter. So that is a quite common regime for any growers. The only growers I know fertilize in winter are those working with extream grow lights to simulate summer or tropical conditions. Terrarium hobbyists or illegal herb growers.

Your fertilizer manufacturer may not like it, but it is still a fact that plants metabolism is dependent on sunlight and that fertilizer may build up to toxic levels if you continue fertilize when uptake is low.