The tree is native to South Korea, China, and Japan. This deciduous species is elegant and easy to grow. The serrated dark green leaves change color from lush green in spring to bright yellow, orange, and red in autumn.

The crown shape has a natural broom form, perfect for bonsai.

Location

Zelkova can be kept indoors, but it needs to be outside in a shaded location during the summer. The plant needs protection from the cold, so in the autumn, when the temperature starts to drop, it should be brought inside. In spring, you can put the tree outside again, provided there are no night frosts.
The plant likes lighted places, but not under the direct sunlight, from which the trunk can quickly overheat. It is necessary to ensure that the tree is lighted evenly from all sides for this pot is periodically rotated.

Temperature regime

The optimum temperature for growth and development is from +15 °C to +25 °C

Soil

Prefers well-drained soil with pH 5.0–7.0.
A specialized bonsai soil or a mixture of Akadama, pumice and organic material can be used (see here).

Watering

Needs regular watering. The soil should not be overwatered. In dry and hot weather, the plant should be sprayed periodically.
Water should be cleaned of impurities, especially lime. It is necessary to stand the water for at least 3 days.

Fertilization

During the winter period, after the leaves have fallen, no fertilization is carried out. After the buds open in spring, feed weekly with a high nitrogen content for the first month, then with solid organic fertilizers once a month throughout the vegetation season.

Repotting

Performed every 2–3 years to refresh the soil and prune roots. Repotting is best done in early spring. If the tree is in a non-deep container repot every 1–2 years.

Shaping and pruning

Regular pruning is important to maintain the shape of the bonsai. Elm trees are usually shaped solely by pinching and pruning, but wire can also be used. Wiring can be done anytime from late spring (after leaves appear) to mid-autumn.
Pruning is done in winter when the branch structure is clearly visible. Foliage is developed by pinching new shoots during the growing season. When at least 4 leaves appear on the new shoots, you should pinch down to 2.
To reduce the size of the leaves, they are removed, leaving only the shoots on the branches. In response, the tree will release a second set of leaves, smaller than the first. Full leaf pruning is not recommended in the same year that the tree is transplanted into a pot.

Winterization

Zelkova should be grown outdoors if possible. Trees grown indoors may remain evergreen, whereas outdoor cultivation will produce a deciduous tree. Care must be taken to ensure that trees do not freeze over when frosts occur. Elms usually though can cope with unfavorable conditions indoors, but they will not be as vigorous as when grown outdoors.

When overwintering indoors, you need a well-lighted, cool place on a sunny windowsill throughout the winter. Humidity levels should be controlled — dry air destroys the plant. Put outside in the spring after the last frosts are over. Keep outdoors — until fall, when the leaves fall naturally.
When wintered outdoors, acclimatized elms are hardy to light frosts, but temperatures below -5 °C can cause thin branches to die back and damage roots, so they should be protected. Frost protection can include placement in cool outbuildings and garages. Trees do not need light during the leaf-free period.

Diseases and pests

Powdery mildew
A fungal disease that covers leaves with a white or grayish downy patina. Leaves may become deformed, dry and fall off.
Provide good ventilation around the crown and avoid overwatering. Use copper or sulfur-based preparations to treat affected areas.
Remove fallen leaves in the fall, as the fungus spores can overwinter in the soil.

Leaf spot
A fungal disease that manifests itself as black spots on the leaves.
Symptoms: black spots appear on the leaves, which gradually grow and can lead to premature leaf fall.
Remove fallen leaves in the fall, as fungal spores can overwinter in the soil.

Aphids
Small insects that feed on plant sap, weakening plants and promoting the spread of fungal diseases.
Sticky discharge on leaves, curled leaves, stunted growth.
Wash the plant with a soapy solution of laundry soap.

Spider mites
Microscopic mites that form thin webs on leaves and shoots.
Leaves become pale, spots appear, and small webs are visible on the underside of the leaf.
Moisten the plant, as mites do not like a humid environment.

Scale insects (Diaspididae)
Small insects covered with a shell that attach themselves to stems and feed on sap.
Small convex brown or black dots appear on the stems and leaves. Leaves may turn yellow and fall off.
In cases of minor infestation, scale insects can be removed manually by wiping the tree with a damp cloth.

General recommendations for prevention

Inspect the plant regularly and frequently for symptoms of disease and pests.
Avoid overwatering and stagnant water, as this can provoke fungal infections.
Keep the pot clean, remove fallen leaves and cut back damaged or diseased branches.
Ventilate and make sure the crown is well ventilated, especially if the elm is growing indoors.