The Chinese elm is an excellent bonsai tree selection. It is a highly adaptable tree that can be grown both indoors and outdoors. When kept indoors as a small bonsai, the tree remains semievergreen. Should you choose to grow the Chinese elm as a larger, outdoor bonsai, the tree will become deciduous.
Plant the Chinese elm bonsai tree in nutrient-rich, well-drained soil. Promote a sandy loam by mixing the nutrient soil with equal amounts of peat compost and fine, clean sand.
Select a container with a depth that is at least equivalent to the trunk's diameter. Place a layer of soil at the bottom of the container. Center the bonsai in the container and fill the container with the remaining soil. Press the soil firmly but gently to support the tree.
Place the bonsai, whether indoor or outdoor, in a location that provides at least 6 to 8 hours of partially shaded to full sunlight each day. Select a location that provides good air circulation and more morning sunlight to prevent foliage burn. Avoid placing the bonsai near sources of extreme hot and cold temperatures.
Water the bonsai regularly, allowing the soil to dry between watering. However, never allow the soil to dry out completely. Avoid drought conditions and overwatering by checking the soil's moisture levels prior to each watering. Stick your finger approximately 1 inch into the soil near the roots. Water the tree when the moisture feels low.
Feed the Chinese elm bonsai during the growing season. Use a well-balanced, slow-release fertilizer that contains nitrogen, phosphorous and potassium. A 10-10-10 (NPK) combination is ideal. Distribute the fertilizer equally and incorporate gently into the soil. Apply the fertilizer every 2 to 4 weeks at half strength. Reduce the applications to monthly during the late fall. Choose a low-nitrogen fertilizer for fall application.
Prune the Chinese elm to promote its framework and intended shape. Keep up with the quickly growing elm by pruning it regularly. Trim the branches to maintain its shape. Do not cut too much as this will promote dieback and weakening. Complete major pruning during the early spring, just before the growing season.
Inspect the elm regularly for signs of disease and infestation. Dust the tree to reduce, if not prevent, airborne fungal diseases. Do not mist. Treat infestations and diseases immediately. Spray the tree with an insecticide or fungicide. Follow the directions carefully. Speak with a local nursery specialist for selection and treatment assistance.
Repot the bonsai to maintain its overall good health. Repot younger, smaller trees every 1 to 2 years. Repot larger trees every 2 to 4 years. Complete the repotting process in the early spring. Always repot bonsais immediately if they have outgrown their pot. Use a fresh soil combination when repotting. Complete a general pruning of the root system during this process. Remove no more than one third of the root system using sharp, sterile scissors. Water lightly after the repotting process is complete.