Ficus trees are beautiful, delicate trees that can last for years and grow to a good size. However, they tend to be picky, dropping their leaves when conditions are not to their liking or if they are moved, even when growing in a container. You will either spend hardly any time at all taking care of the tree short of watering it, or you will be constantly trying to figure out what is troubling it. When it develops health problems, there are several things that you can do to give it a chance to survive.
Water the tree if leaves start to drop during hot weather. Watering even once or twice a day is OK. Check the soil with your fingers to make sure the water is not just running out the bottom of the container. If it is running out, try covering the holes so the plant has time to absorb it.
Water as normal and keep an eye on the tree if the leaves start to fall after moving it. Ficus are notorious for dropping leaves after a move, even it they are used as indoor plants. They should go back to normal after a while.
Empty out the planter and clean the roots off with water if it is infested with bugs. Replace the bad soil with new soil and replant. Trim off any limbs that might have died as a result of the issue. The leaves might fall off after the re-potting due to all the movement.
Trim limbs or branches that you determine are dead. This will keep the plant from using energy on an area that cannot be saved. If the tree was exposed to frost, you will need to wait for new growth to appear. Then trim limbs that have no growth.
Keep the tree in moderate light so it gets enough sun during the day. Direct light will likely be too hot for it, especially during summer months, and will dry out the soil.