Is this bonsai in trouble?

Question

This is a bonsai fig tree, which I bought maybe two months ago. As you can see in this photo, it's losing leaves at a good clip:

However, a closer look shows that it's also sending up branch extensions (probably not the correct term) with new leaves:

So what's going on here? For context, I try to stay on top of the watering, but the tree drinks unpredictably, so I'm never sure when I'm going to find the soil dried out. There's a fluorescent grow light overhead, lit eight hours a day.

What, if anything, does the tree need?

Answer 1

Sporadic watering is more likely the issue. Drying out a bonsai plant will lead to leaf drop. Plants do have a natural rhythm on when they need water, it slowly increases in spring and slows down slowly in late summer/fall. Once, you figure out the rhythm it becomes easier to predict when to check to see if they need water. Remember bonsai dry out much quicker than most plant. They need a lot of water, because they are in shallow pot with extremely well draining potting medium.

If you have difficulties knowing if it's time to water, use something as simple as a bamboo skewer. Insert it in the pot. The next time you think it is time to water, pull it out and check it. Look at it and feel it. If it is wet it is too early, if dry its too late. If the stick does not appear wet, but feels moist it is time to water.

You also do not put your grow light on long enough. The general rule is 12-14 during dormant season and 16-18 during the growing season. This plant does not really have a natural dormant season, so you should double the amount of light you are providing. You do have a window near-by so you do not need to go all the way to 18 hours, but you should not do anything less than 12. The light should also be about 6-8" above the plant. Also, fluorescent grow light bulbs should be replaced every 2 years.

Answer 2

In an earlier question about this plant after it first arrived in the house it seemed to be in quite good condition with even foliage and quite nice shape. Clearly it has taken a turn for the worse. A reason for consideration is humidity in the air. From the design of the window in the room the area might call for some domestic heating, even though outside we don't see any snow, so with the heating season comes a dramatic drop in humidity in the air. Ficus do a lot better in moist air, and if you have recently switched on additional heating without compensating boost in humidity then this might have caused the leaf drop.

With reduced natural light the growth slows, calling for less watering if the humidity is right. My guess is there is a battle going on between moist roots and dry leaves - The moist roots are stimulating unnecessary root growth which the plant tries to balance with new shoot growth at the expense of mature leaves. Raising the humidity and reducing water at the roots might help get back to a state of balance.