- Mature height
- 1m to 6m (approx.) (variable depending on species, very slow-growing; this refers to trunk height)
- Mature width
- 1m to 3m (leaf crown spread)
Xanthorrhoea species, sold here as Grass Tree or Black Boy Tree, are slow growing Australian natives that form a blackened woody trunk topped with a dense skirt of fine, linear foliage. Mature plants send up a tall cream flower spike that stands well above the crown, packed with nectar.
They reach 1 to 6 metres tall depending on species and age, with a leaf crown 1 to 3 metres across, and grow only about 1 to 3 centimetres a year. Full sun, sharp drainage and lean soil suit them. They handle drought, poor ground, frost and fire, and are at home from Perth to Sydney and well inland.
Grass trees are used as sculptural focal points in native, coastal and dry gardens, in rockeries, courtyards and civic entry statements. They pair well with low native shrubs, succulents and gravel mulch. Because they grow so slowly, an established specimen carries an age and character that cannot be produced any other way.
Frequently Asked Questions
About Grass Tree
What is a Grass Tree?
Xanthorrhoea is a genus of slow growing Australian natives with a thick, fire blackened trunk and a crown of stiff, grass like leaves. They are also known as Black Boy Trees, an older name still in circulation. The trunk is not true timber but a compacted mass of old leaf bases bound together with resin.
How fast do Grass Trees grow?
Very slowly, about 1 to 3 centimetres of trunk a year. A plant with a metre of visible trunk has usually been growing for several decades, which is why advanced specimens are sold on trunk height rather than pot age. Nothing in cultivation speeds this up meaningfully, so buy the size you want to live with.
How big do Grass Trees get?
Between 1 and 6 metres tall depending on the species and how old the plant is, with a leaf crown spreading 1 to 3 metres. Most landscape specimens sit well under the upper figure. The flower spike adds further height in season, standing up to around 2 metres above the crown.
Is the Grass Tree drought tolerant?
Strongly drought tolerant once established. These plants evolved on nutrient poor, freely draining soils and are adapted to long dry periods, so summer watering is rarely needed after the first year. The common cause of death in gardens is the opposite problem, roots left sitting wet in heavy clay or in an over irrigated bed.
Does it need sun or shade?
Full sun. Grass trees need open, unshaded positions to keep the crown dense and the plant healthy, and they thin out and decline under trees or against shaded walls. Reflected heat and exposed sites are no trouble at all. Give them the hottest, driest, best drained corner available.
When does a Grass Tree flower?
Flowering is sporadic rather than annual, most often through late winter into spring and frequently triggered by fire, heat or a good season. The spike carries thousands of small cream flowers and draws honeyeaters, native bees and other insects. A plant may flower several years running, then skip several years entirely.
How do I care for a Grass Tree?
Plant it high in free draining soil or on a raised mound and do not disturb the roots. Water sparingly through the first summer, then leave it alone. Avoid fertiliser, particularly anything high in phosphorus. Old leaves can be trimmed back to tidy the skirt. Keep irrigation and lawn sprinklers away from the trunk.