Xanthorrhoea quadrangulata
Yacka
Overview
Xanthorrhoea quadrangulata is a slow-growing grass tree that forms a dense crown of long, narrow, grass-like leaves above a stout trunk, reaching 6-13 feet (2-4 m) tall over many decades. The leaves are stiff and four-sided in cross-section, 1.5-3 feet (45-90 cm) long and only about 0.1 inch (2-3 mm) wide, arching out from the growing point in a rounded skirt. Older leaves die and form a thick brown collar around the trunk. From late spring a flowering spike rises well above the foliage, made up of a bare lower stalk and a dense cylindrical spike of small cream flowers up to 3 feet (90 cm) long. Flowering is often heavier in the seasons after fire. The plant is native to hilly country in South Australia, growing on poor, stony, free-draining soils in open woodland and heath. It develops a deep root system and a fire-resistant trunk, recovering from bushfire by reshooting from the crown. Growth is very slow, with trunk height increasing only about 0.4-0.8 inch (1-2 cm) per year, so mature plants are many decades old and slow to replace if lost.
Native Range
Xanthorrhoea quadrangulata is native to South Australia, including the Mount Lofty Ranges, Flinders Ranges, and nearby hills. It grows on stony, free-draining soils in open eucalypt woodland and heath.Suggested Uses
Xanthorrhoea quadrangulata is grown as a long-lived feature plant in low-water and native gardens on free-draining ground, and in restoration of South Australian woodland and heath. Its slow growth and drought tolerance suit dry, stony sites and rockeries.How to Identify
Appearance
Size & Dimensions
Height6' - 13'
Width/Spread4' - 8'
Reaches mature size in approximately 30 years
Colors
Bloom Information
A tall cylindrical spike of small cream flowers appears from late spring into summer, roughly October to January in South Australia. Flowering is often stronger in the seasons following bushfire. The spike holds nectar-rich flowers that draw insects and birds before drying to a woody seed spike.
Detailed Descriptions
Foliage Description
green to grey-greenGrowing Conditions
Sun Requirements
Requires 6-12 hours of direct sunlight daily
• Full Sun: 6+ hours of direct sunlight
• Partial Shade: 3-6 hours of direct sunlight
• Full Shade: Less than 3 hours of direct sunlight
Care & Maintenance
Care Guide
Xanthorrhoea quadrangulata grows in full sun on stony, sharply drained, low-fertility soils and tolerates extended drought once established. It grows poorly in rich soils and with heavy watering, which can lead to root rot. Plants are very slow to establish and are usually grown from seed, taking years to form a visible trunk. It withstands frost and heat in USDA zones 9-10. Transplanting established grass trees often fails because of fungal root rot, so plants are usually grown in place from a young age rather than moved. Growth is measured in decades rather than years.Pruning
Pruning is limited to removing spent flower spikes and trimming the dead leaf skirt if a clean trunk is wanted. The brown skirt of old leaves can be left in place, as it shelters the trunk. Cutting into the single growing crown kills the plant.Pruning Schedule
J
F
M
A
M
J
J
A
S
O
N
D
summer
Container Growing
✓ Suitable for container growing
Minimum container size: 10 gallons