Wilt, droop and brittle branches are true signs of an ailing bonsai. Whether it is has been neglected or infected, a dying bonsai requires immediate attention if you intend on saving it. Not every bonsai can be saved from a dying state, but with some care and attention, your bonsai may have a chance.
Use sharp, sterile pruning shears to remove any areas of the bonsai that are cannot be saved, such as dead or broken branches, and wilted foliage and stems. Cut back the branches to the trunk or leader.
Look to see if the cambiums of the cut areas are green and fairly healthy. Expect for your bonsai to recover if the cambium is healthy as this shows that the tree is still viable. Do not panic if the cambiums in some areas are dry while others are not.
Remove your bonsai from its container to root prune and repot it. Inspect the root system thoroughly. Use sharp, sterile shears to prune away dead and wilted roots. Remove all infected, dead and damaged roots from the system. Cut those areas back to the root mass.
Place the bonsai in a clean glass container and fill it with tepid water so that it reaches just past the root system. Allow the bonsai to rest in the water while you clean your potting container and create your soil mixture.
Wash your container with a mild detergent and warm water. Be sure to remove any particles that are stuck to the insides of the container. Create an open and porous soil mixture that has good water retentive qualities. Incorporate equal amounts of nutrient rich potting soil, perlite and pure sphagnum moss. Mix the items thoroughly for a balanced loam.
Line each of the drainage holes with wire mesh and then fill the container a third of the way with your soil mixture. Center the bonsai in the container and fill it the rest of the way with soil. Take your bonsai, and place it in a sink or bucket if it is fairly large. Fill the sink with tepid water so that it reaches about 1 inch above the container's surface. Allow your bonsai to sit in the water until the bubbles cease to rise.
Remove your bonsai from the water and allow the water to flow from the drainage holes. Place the bonsai in a warm, partially shaded location. Choose a well-ventilated location to promote good cell development.
Give your bonsai some time to regenerate. Be patient as the bonsai may wait until the following growing season before it shows true signs of revitalization. Irrigate your bonsai deeply and infrequently with tepid water. Allow the soil to dry slightly between irrigations to avoid overwatering.