The Japanese Zelkova (Zelkova serrata) is one of the most highly valued species in bonsai.
This extensive guide details the essential care requirements for maintaining a healthy and refined Japanese Zelkova bonsai.
Position and Light Requirements
The Zelkova is a vigorous, sun-loving tree that requires optimal light exposure for dense growth and colour.
- Growing Season (Spring to Autumn): Place the Zelkova in full sun throughout the day. It thrives on maximum solar energy, which encourages vigorous growth, strong back-budding, and the reduction of leaf size.
- Airflow: Ensure excellent air circulation around the foliage, which helps prevent fungal issues and supports healthy growth.
Watering
The Zelkova is a thirsty, fast-growing tree, especially during the warm months.
- Principle: Water thoroughly when the surface of the soil begins to look dry or lightens in colour.
- Avoid: Never allow the root ball to dry out completely, as this quickly stresses the tree, causing leaves to brown and drop.
Fertilisation
Consistent and heavy feeding is mandatory to support the Zelkova's rapid growth and its ability to withstand continuous heavy pruning and defoliation.
- Timing: Begin feeding heavily in early spring once the buds open and continue through late summer/early autumn. Stop feeding when the leaves begin to change colour in the autumn.
Winter Care and Dormancy
As a deciduous tree, the Zelkova requires a mandatory cold dormancy period.
- Dormancy Requirement: The tree needs temperatures consistently below 7C for at least 8 to 12 weeks.
- Protection: Place the pot in an unheated garage, shed, or cold frame when temperatures consistently drop below -4C. Insulate the pot with mulch or bury it.
Pruning and Styling (Refinement)
Pruning is the most important technique for creating the Zelkova's famous fine branching.
- Structural Pruning (Winter): Major cuts to establish the primary structure should be made during winter dormancy. Use concave cutters and seal large wounds.
- Branch/Shoot Pruning (Growing Season): This is the core refinement work. When new shoots extend to 4–6 leaves, cut them back aggressively to 1 or 2 leaves.
Repotting and Soil
- Frequency: The Zelkova is a fast root grower and requires frequent repotting: every 1–2 years for young trees, and every 2–3 years for mature trees.
- Timing: Repot in early spring just before the buds begin to swell.
- Soil: Use a very fast-draining, airy, granular bonsai soil mix (Akadama, Pumice, Lava Rock).
Pests and Diseases
The Zelkova is relatively resistant but watch for common issues.
- Pests: Primarily susceptible to Aphids (on new, soft growth), Leaf Beetles, and occasionally Spider Mites (in hot, dry conditions). Treat with Insecticidal Soap or Neem Oil.