The Casuarina, also known as female oak, ironwood or reswood, is a tree whose appearance evokes pines and other conifers, although from a botanical point of view, it belongs to a completely different family. Native mainly to Australia and diverse pacific islands, has successfully adapted to temperate and coastal climates around the world, where it is especially valued for its hardiness and low maintenance. Want to discover why the Casuarina is so prized by landscapers and gardeners?
What is Casuarina? Botanical description and origins
The gender Casuarina belongs to the family Casuarinaceae, grouping evergreen trees and some shrubs, with about 15 accepted species out of more than 70 described. They are characteristic of coastal areas, although their presence extends from Australia and Asia to Polynesia and Malaysia. Due to their distinctive foliage, they are often confused with conifers, but their thin, segmented branches have leaves reduced to scales arranged in rings at the nodes, while the photosynthetic function falls on the thin, green stems, known as cladodes.
These plants can reach Meters 30 Depending on the species and conditions, they have straight or slightly twisted trunks and rough or fissured, brown to grayish bark, which can peel off in longitudinal strips. Their light, drooping appearance makes them well-suited as ornamental elements, windbreaks, and as a fixative for sandy soils.
Main characteristics of the Casuarina
- Evergreen: It keeps its leaves all year round, although some species are semi-deciduous under extreme conditions.
- Medium-fast growth: Once adapted to the terrain, it can grow rapidly, especially in fresh, well-drained soils.
- Scaly leaves and needle-like branches: The real leaves are small scales, while what looks like needle-like foliage are actually branches with photosynthetic function.
- Resistant to salinity and drought: It tolerates sandy, saline soils and periods of low rainfall, making it ideal for coastal areas and poor soils.
- Powerful root: They have deep, extensive roots capable of anchoring soil and preventing erosion. Some species establish symbiosis with nitrogen-fixing bacteria, enriching the substrate.
- Unsightly flowers: It has separate male and female inflorescences, without petals, which can be located on the same plant (monoecious) or on different plants (dioecious).
- Woody fruits: The fruits are small cones similar to conifer pine cones, containing winged seeds that are easily dispersed by the wind.
In addition to its ornamental value and ecological, stand out for their hardwood, widely used for posts, fences and as fuel, as well as for wind control and soil protection against sea salt.
Main species of Casuarina
- Casuarina cunninghamiana: Known as river oak or Australian pine, it is the tallest species of the genus, reaching up to 30 meters. Its crown is pyramidal, with green branches very similar to pine needles, and it tolerates temperatures as low as -10°C. It is predominant in eastern Australia.
- Casuarina equisetifolia: Known as the Australian pine, Paris pine, or horsetail casuarina, it can reach 25 meters in height and often branches close to the ground. It is highly resistant to salinity and can withstand temperatures down to -7°C. It grows from Australia to Myanmar, Bangladesh, Polynesia, and Malaysia.
- Casuarina glauca: Recognizable by its blue-green branches, it is found on the east coast of Australia and grows to 15 meters. It is notable for its roots forming symbiosis with the bacteria Frankia, which fixes nitrogen in the soil.
- Casuarina obesa: Swamp oak, or swamp oak, is native to New South Wales and Victoria, Australia. It typically grows no taller than 10 meters. It tolerates heavy (clay) and saline soils.
- Casuarina stricta: The casuarina pendula, which grows to a maximum height of 10 meters. Its rounded crown has drooping green branches, making it ideal for poor or saline soils. It can withstand temperatures down to -5°C.
- Other relevant species:
- Casuarina torulosa: With a narrow crown and pendulous terminal branches, with pinkish coloration on young branches.
- Casuarina cristata and Casuarina teres: Less common in gardening, but present in specialized botanical collections.
Each of these species offers unique characteristics in terms of resistance, height, and adaptation, allowing you to choose the most appropriate one based on the climate, function, or planting environment.
Requirements and care of the Casuarina
Location and sun exposure
The Casuarina requires a location in full sun. It is essential for your vigorous development and proper growth. Although it's not considered a species with aggressive roots, it's best to plant it at least 5 meters away from buildings, walls, or pavements, as its root system expands significantly in search of water and nutrients.
Soil type and plantation
Its tolerance to soil types is very high: grows in sand, poor, saline soils and marginal plotsIt prefers a well-drained substrate, although it tolerates occasional waterlogging. To improve its growth, it's advisable to add organic matter (peat, compost, or leaf mulch) and some coarse sand to facilitate drainage. The ideal pH is slightly acidic to neutral., but adapts to wide ranges.
The plantation This is usually done in late winter or early spring, once the risk of frost has passed. It's best to repot when the roots have colonized the pot and are emerging from the drainage holes.
Irrigation
During the first year, It is necessary to water 2 to 3 times a week in summer and reduce during cold periods. With age, casuarina can withstand several days without watering and is considered a drought-resistant speciesAfter the adaptation period, water should only be done when the substrate is dry.
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Considering its rusticity, the Casuarina does not require specific fertilizers, but can benefit from applications of organic fertilizer (manure, compost, guano) in early spring. If grown in pots, it is recommended to use a balanced liquid fertilizer once a month during the active growing season. A good fertilizer should include macronutrients (nitrogen, phosphorus, potassium) and micronutrients (iron, manganese, copper, zinc, boron, molybdenum).
Pruning
It is not essential to prune the Casuarina, except for removing dry, diseased, or damaged branches in late winter or early spring. Young specimens can be lightly pruned to maintain their compact appearance. Excessive pruning reduces the tree's ornamental value and overall vitality.
Multiplication
Propagation is preferably carried out by seeds. In spring, the woody fruits are harvested and, once dried, release seeds that, when stored in dry conditions, remain viable for 1 or 2 years. Planting should be done in pots with a light, porous substrate, covered with a thin layer of soil. It is recommended to treat the substrate with fungicide to prevent fungal problems, especially in humid environments. Propagation is also possible by semi-woody cuttings, cut with a disinfected tool; these are planted in a mixture of peat and sand, and the humidity is maintained high until they root.
Plagues and diseases
The Casuarina is a robust plant and not very prone to pests or diseases.However, in flooded soils, it can be attacked by fungi (especially oomycetes) that affect the roots. In exceptional cases, caterpillars and beetles may feed on tender leaves or branches.
Toxicity and compatibility
There are no reports of toxicity of Casuarina for pets or domestic animals, but supervision is recommended in gardens shared with animals.
Uses of Casuarina
- Ornamental: Ideal as a single specimen, in rows or forming green screens in large gardens, public parks, avenues and coastal urban areas.
- Windbreaks and salinity barriers: Its rapid growth and resistance to saltpeter have made it popular as a forest curtain and barrier against strong winds, especially in coastal areas.
- Soil fixer: The powerful root system and nitrogen-fixing capacity help stabilize dunes, combat erosion, and improve degraded soils.
- Wood and firewood: Its hardwood is used for posts, construction, charcoal production and high-quality firewood.
- Urban and rural reforestation: Thanks to its hardiness, it is chosen for revegetation plans in warm, coastal areas and poor soils.
- Bonsai: Its elegant appearance and stylized branches facilitate the formation of miniature specimens of great beauty.
The casuarina is a versatile, hardy tree of great landscape and ecological value. Its ability to thrive in poor soils, withstand drought and salinity, and its low maintenance requirements make it an ideal choice for sustainable gardens, reforestation, and coastal protection. If you're looking for an ornamental species with multiple benefits and ease of care, the casuarina is a safe bet for any green space.