Zelkova - Japanese Elm: Planting and Care

Botany and Description

The Zelkova genus includes 6 species distributed across the northern hemisphere and belongs to the Ulmaceae family, like the Elm.

• Zelkova serrata or Japanese Zelkova: this is the most common species and the most widely cultivated for ornamental and landscaping purposes. It is native to Japan, Korea, and China.
• Zelkova carpinifolia: also known as Caucasian Zelkova, Caucasian Elm, or Siberian False Elm, it is a species native to Southern Europe and Western Asia.
• Zelkova sinica, endemic to the northeastern regions of China.
• Zelkova sicula or Sicilian Zelkova, endemic to Sicily (and discovered by chance by students in 1991).
• Zelkova abelicea or Cretan Zelkova, endemic to the island of Crete.
• Zelkova schneideriana, native to China.
• Two other Zelkova species, now extinct, can also be mentioned: Zelkova ungeri (Eurasia, a fossil species from the Miocene) and Zelkova nervosa (North America, a fossil species from the Eocene).

Zelkova serrata on the left (© Dan Deck), and on the right, the Cretan Zelkova or Zelkova abelicea.

Zelkovas typically grow in temperate zones, in well-drained and nutrient-rich soils. Most zelkovas have a pyramidal shape when young, with lower branches that rise as the tree ages. At maturity, the tree’s form can become more spreading and rounded.

Zelkovas are deciduous trees. The leaves are simple and oval, lanceolate or heart-shaped, with a pointed tip. They generally measure between 3 to 10 cm in length and are finely serrated along the edges. The leaves are dark green and glossy on top and lighter underneath. In autumn, zelkova leaves turn shades of yellow, orange, and red before falling. Additionally, zelkova leaves are arranged alternately on the branches, giving the tree an airy and elegant appearance.

Foliage of Zelkova carpinifolia

Zelkovas are monoecious species, meaning they have both male and female flowers on the same tree. Flowering occurs in early spring, in March or April, before the leaves appear. The flowers are small, green, and inconspicuous, clustered in hanging groups along the branches. Male flowers produce pollen, while female flowers have a small pistil at the centre. Zelkova pollination is wind-driven, as the flowers lack nectar or scent to attract pollinating insects.

After pollination, the female flowers develop into small green drupes that ripen in autumn. The drupes measure about 3 to 5 mm in diameter and contain a single seed. The ripe drupes are light brown and are consumed by birds in winter. These fruits add aesthetic interest to the tree in autumn and provide a food source for wildlife.

Zelkovas are often used for ornamental purposes and landscaping due to their elegant silhouette and dense foliage. Their hard and durable wood is also used for furniture making, musical instruments, and other craft items.

Our Finest Varieties

Zelkova serrata

This large and beautiful deciduous tree, reaching 18-20 m in height, is recognisable by its short, stocky trunk topped with a broad, airy crown. Like its relative, the Zelkovia carpinifolia, it makes an excellent alternative to the elm.

• Flowering time May, June
• Height at maturity 18 m

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Zelkova serrata Variegata

A variegated variety of the Japanese Zelkova, much more compact than the original species. Slow-growing, it is well-suited to small gardens, forming a small tree with a branched silhouette and spreading habit.

• Flowering time May
• Height at maturity 5 m

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Zelkova serrata Green Vase

A good shade tree reaching 15 m in height, with a semi-open crown displaying a beautiful flared shape. This variety bears stunning dark green deciduous foliage that turns golden yellow, bronze, and orange in autumn.

• Flowering time May, June
• Height at maturity 15 m

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Zelkova serrata Goblin

The 'Goblin' cultivar stands out for its very limited growth at maturity, reaching about 1.20 m in height and 90 cm to 1 m in spread. It develops a short, stocky trunk from which spreading main branches rise, giving way to finer branchlets.

• Flowering time May, June
• Height at maturity 1,20 m

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Planting a Zelkova

Where to Plant?

The zelkova is a robust and adaptable tree that can be planted in many regions and soil types. However, for optimal growth, it is best to plant a zelkova in a sunny or partially shaded location, in well-drained and fertile soil.

The zelkova can tolerate a wide range of soil pH levels, but it prefers slightly acidic to neutral soils. Avoid planting the zelkova in highly alkaline or saline soils.

The zelkova is resistant to urban conditions and can be planted in urban or industrial areas where pollution levels are high. It is also a disease and pest-resistant tree, making it popular for parks and public gardens.

It is important to choose a location where the zelkova will have enough space to grow. Ensure the tree is planted at an appropriate distance from buildings, other trees, and infrastructure to avoid long-term damage.

Zelkova carpinifolia (© Wendy Cutler)

When to Plant?

The best time to plant a zelkova is during the dormant season, that is, in late autumn or early winter, when the tree is at rest and the soil is not frozen.

How to Plant?

1. Prepare the soil: weed the planting area and loosen the soil with a fork or spade. If the soil is heavy or clayey, improve it by adding compost or manure to enhance its structure and fertility.
2. Dig the planting hole: dig a hole two to three times the size of the root ball of the zelkova. The bottom of the hole should be slightly wider than the root ball to allow the roots to spread easily.
3. Place the tree in the hole: carefully remove the tree from its container and place it in the planting hole. Ensure the top of the root ball (the root collar) is level with the ground.
4. Fill the hole: pour the loosened soil around the root ball to fill any gaps. Lightly firm the soil to remove air pockets.
5. Water thoroughly: water the tree generously immediately after planting to help establish the roots and eliminate any remaining air pockets between the soil and roots. Keep the soil moist for the first few weeks after planting.
6. Protect the tree: protect the tree from damage caused by animals or weather by installing a fence or stake. Do not compact the soil around the tree to avoid damaging the roots.

The Care of a Zelkova

Watering

Watering is a vital aspect, especially for young trees. During the first few years, ensure the soil remains slightly moist, without saturating it. Once established, the Zelkova serrata tolerates drought well but appreciates regular watering during periods of intense heat.

Fertilisation

Fertilisation contributes to vigorous growth. Use a balanced fertiliser (NPK: 6-4-4, for example) in spring to stimulate the development of new leaves. Additional fertilisation in autumn supports the tree’s health during winter.

Pruning

Pruning, if necessary, should be done carefully. Remove dead, diseased, or crossing branches to promote good air circulation and adequate light penetration. Pruning is best done in late winter, before budding begins.

Winter Protection

In winter, young trees may require protection from cold and frost. Mulching around the base of the tree helps maintain soil temperature and preserve moisture.

Foliage of a Zelkova serrata (© Olive Titus)

Diseases and potential pests

Trees of the Zelkova genus, although resistant to many diseases and pests, are not completely immune to certain issues. Here are the main health concerns that can affect Zelkova trees:

• Dutch Elm Disease: Although less susceptible than other elms, Zelkova can be affected by this fungal disease transmitted by beetles. It causes wilting and death of branches. Rigorous monitoring and control of insect vectors are essential for prevention.
• Anthracnose: This fungal disease causes brown or black spots on leaves, potentially leading to premature leaf drop. It typically develops in humid conditions and can be controlled by ensuring good air circulation and applying fungicides if necessary.
• Root Rot: This can occur if the tree is planted in poorly drained or overwatered soil. Prevention is the best strategy, ensuring proper drainage and avoiding excessive watering.
• Aphids: These small sap-sucking insects can infest leaves, causing deformation and the production of honeydew. They often attract ants and can encourage the growth of sooty mould.
• Scale Insects: These pests attack leaves and branches, feeding on sap and weakening the tree. They are harder to eliminate and may require repeated treatments.
• Cankers: Bacterial or fungal infections can cause cankers on the trunk and branches. These appear as areas of dead tissue and can significantly weaken the tree.
• Powdery Mildew: A fungus causing a white, powdery coating on leaves. It is generally more of an aesthetic issue than a serious threat to the tree, but can reduce the tree’s vigour if the infestation is severe.

To protect Zelkova trees from these issues, it is recommended to maintain good garden hygiene, perform regular sanitary pruning, and ensure appropriate watering and fertilisation.

Multiplying a Zelkova serrata

How to pair this tree?

The combination of Zelkova serrata, or Japanese Elm, with other plants in your garden can create a harmonious and aesthetically pleasing space. To achieve this, it is important to choose plants with similar needs in terms of sunlight, watering, and soil type.

Perennials such as Hostas, with their broad leaves, offer an interesting contrast under the canopy of the Zelkova. They appreciate well-drained soil and can tolerate the partial shade created by the tree. Astilbes, with their feathery blooms, add texture and colour beneath the Zelkova. They thrive in similar soil and light conditions. Pachysandra terminalis, a shade-tolerant ground cover, can form a lush green carpet under the Zelkova, creating a natural woodland effect.

Shrubs such as Azaleas and Rhododendrons, which prefer slightly acidic to neutral soils, can harmonise beautifully with the Zelkova. Their spring blooms provide a colourful contrast. Hydrangea macrophylla and serrata are also excellent choices, with their large flowers adding colour and texture in summer.

Finally, some spring bulbs such as daffodils, muscari, and tulips can be planted around the Zelkova for a burst of colour in spring.

Surrounding the Zelkova serrata: Astilbe arendsii ‘Erika’, Hydrangea serrata ‘Kiyosumi’ (©Peganum), Pachysandra terminalis and azalea

Anecdotes

• A link to the past: Zelkovas are often considered “living fossils”. They are closely related to elms, but unlike many elms, Zelkovas have survived the Dutch elm disease epidemics that decimated elm populations across Europe and North America. Their resistance to this disease makes them particularly valuable as witnesses to ancient landscapes.
• Hiroshima survivors: An astonishing fact concerns the Zelkova serrata that survived the atomic bomb in Hiroshima in 1945. Despite the massive destruction, several of these trees not only survived the explosion but continue to thrive today. They have become symbols of resilience and renewal, inspiring people around the world.
• An ancient currency: In some regions of Georgia, Zelkova wood was so valuable that it was used as a form of currency in antiquity. Its strength and beauty were highly prized, making Zelkova wood a precious resource for trade and transactions.
• A star of Asian gardens: The Zelkova is a traditional element of Japanese and Chinese gardens. Due to its elegant shape and ability to be pruned, it is often used in the art of bonsai. Some Zelkova bonsai are centuries old and are considered true works of art, reflecting the patience and skill of their cultivators.