Mountain Ash (Eucalyptus regnans)

Eucalyptus regnans, commonly known as the Mountain Ash, is a magnificent and iconic species native to the southeastern Australian states of Tasmania and Victoria. Renowned for its impressive height, straight trunk, smooth grey bark and glossy lance-shaped leaves, it is the tallest flowering plant in the world.

It often grows in pure stands in tall wet forests, sometimes with rainforest understorey, and in temperate, high-rainfall areas with deep loam soils. Many trees have been logged, and mature forests dominated by Eucalyptus regnans have been found to store more carbon than any other forest on the planet.

Tree Height and Spread: Eucalyptus regnans is a towering species known for its extraordinary height. In its native habitat, it can reach over 100 meters, making it one of the tallest trees globally, alongside the Coastal Redwood and Douglas Fir.

Its spread can vary widely depending on growing conditions but typically ranges from 9 to 15 meters. The tree’s growth habit is generally straight and majestic, with a narrow canopy. It can grow to 1 meter per year, with mature specimens growing to 2 meters per year.

Preferred Soil Type and pH: Mountain Ash thrives in deep, well-drained soils with good moisture retention. It prefers soils rich in organic matter, such as deep, loamy, free-draining soils. While it can tolerate a range of soil pH levels, it generally prefers slightly acidic to neutral soils, with a pH range of 5.5 to 6.5. Regular soil testing can help ensure the pH is optimal for healthy growth.

Climate and Environmental Requirements: This species is well-suited to temperate climates with mild to cool temperatures. It thrives in regions with reliable rainfall and is commonly found in moist, mountainous areas. Mountain Ash is cold-hardy, does best in southeastern Australia, and can tolerate snowfall. It requires adequate sunlight to thrive and prefers locations with total sun exposure.

Light Requirements: Eucalyptus regnans prefers full sun and should be planted in locations that receive at least six to eight hours of direct sunlight daily. Adequate sunlight promotes vigorous growth and helps maintain the tree’s straight trunk and narrow canopy. The tree may become leggy or develop irregular growth patterns in shaded conditions.

Watering and Fertilising: Proper watering is essential, especially during the tree’s establishment phase. The soil should be kept consistently moist but not waterlogged. Once established, Mountain Ash becomes more drought-tolerant and can withstand periods of reduced water availability. However, mulching and regular watering during dry spells is still recommended, particularly in warmer climates.

Fertilisation is generally not required if the tree is planted in nutrient-rich soils. However, in soils with low fertility, applying a balanced, slow-release native fertiliser in late winter / early spring can support healthy growth. It’s important not to over-fertilise, as excessive nutrients can lead to imbalances and affect the tree’s overall health.

Pruning and Maintenance: Eucalyptus regnans typically require minimal pruning, especially in natural or forested settings. However, pruning may be necessary in urban or landscaped environments to remove dead, damaged, or diseased branches. Shaping the tree can also be done to maintain its straight trunk and narrow canopy. Pruning is best carried out during the dormant season to minimise stress on the tree.

Propagation: Eucalyptus regnans is primarily propagated through seeds. The seeds are small and enclosed within woody capsules, which typically mature and release seeds in late summer or early autumn. Seed propagation requires stratification to break dormancy and improve germination rates.

Uses: Mountain Ash has several uses, including timber production, landscaping, and carbon sequestration. It is valued for its high-quality wood used in construction, furniture-making, and paper production. In landscaping, it is often planted as a specimen tree in parks, gardens, and larger landscapes, where its impressive height and majestic form make it a standout feature.

Eucalyptus regnans, the Mountain Ash, is a remarkable species known for its towering height and stately presence. It is valuable to diverse landscapes, whether grown for timber, environmental benefits, or ornamental value. Providing the right growing conditions, including well-drained soil, adequate sunlight, and regular watering, ensures the health and vitality of this iconic Australian tree.