The Japanese zelkova, or Zelkova serrata, is a semi-evergreen tree of the elm family (Ulmaceae). Carrying the characteristics of the elm, this tree can reach natural heights up to 60 feet tall, sometimes larger, and develops a natural vase shape. The dark green foliage of the zelkova changes to hues of yellows and bronzes in the fall and it makes an excellent choice for bonsai. When used for bonsai, the Japanese zelkova adjusts to its growing environment, thriving as an indoor evergreen and a deciduous outdoor bonsai. While indoor zelkova bonsais thrive well inside throughout the year, this bonsai does benefit from outdoor placement during its growing season.
Place the Japanese zelkova bonsai in a cool, sunny location that receives at least six hours of full sunlight each day. Choose a location that is away from heating vents and other sources of direct temperature variations, such as patio grills and air conditioners.
Irrigate the Japanese zelkova as required to maintain an evenly moist environment, as recommended by Bonsai4me. Develop a habit of checking the soil prior to each watering and only watering when the soil feels somewhat dry. Apply these irrigation habits to both the indoor and outdoor zelkova bonsai. Never allow the zelkova to dry out completely.
Feed the Japanese zelkova twice monthly from early spring through late fall. Choose a well-balanced, slow release fertilizer with micronutrients, such as a 20-20-20 or 10-10-10. Distribute the fertilizer evenly throughout the tree, as recommended by Absolute Bonsai, and always apply at half strength. Irrigate the feed thoroughly into the soil.
Prune the Japanese zelkova in the early spring just before the end of its dormancy. Use sharp, sterile pruning shears or scissors to complete the cuts. Follow the recommendations of Bonsai Gardener and trim back the shoots leaving no more than two leaves per stem. Remove any dead or dying branches or stems to redirect the bonsai's energy to healthy areas. Thin out the interior foliage to promote good air circulation and increase light penetration throughout the zelkova.
Repot the Japanese zelkova bonsai about every two years. Remove the zelkova from the container and place it on a clean, flat surface. Gently remove the excess soil from the root system. Inspect the roots closely. Use sharp, sterile scissors to remove any dead, dying or wilted roots from the system. Avoid removing more than one third of the system to prevent injury.
Select a potting container that is slightly larger than the original potting container. Follow the general rule as defined by Bonsai4me and select a container with a depth that is equivalent to or a little greater than the diameter of the zelkova's trunk. Ensure that the container has several drainage holes at the bottom to allow the excessive water to pass evenly from the container.
Use fresh bonsai soil to repot the Japanese zelkova. Purchase the soil or mix equal amounts of nutrient rich potting soil with organic compost and clean, fine sand. Incorporate the mixture thoroughly for an even combination.
Fill one third of the well-drained potting container with soil. Position the zelkova in the container and fill the container with the remaining soil. Make sure that no bare roots are showing from the surface and press the soil firmly around the zelkova to secure its position. Consider the recommendations of Bonsai for Beginners and cover the surface of the pot with a thin layer of stones to protect the soil's moisture levels.