Dianella caerulea
Blue flax-lily
Overview
Dianella caerulea is an evergreen rhizomatous perennial forming clumps of strap-shaped leaves 12-36 inches (30-90 cm) tall and 18-36 inches (45-90 cm) wide. Leaves are folded along the midrib into a V in cross section, 0.4-0.8 inch (10-20 mm) wide, dark green to blue-green, with sawtooth ridges on the keel and margins that cut skin drawn along them. Flowering panicles rise 6-24 inches (15-60 cm) above the foliage and branch openly, carrying nodding flowers 0.5-0.8 inch (12-20 mm) across with six blue to violet tepals and yellow anthers on swollen filaments. A few flowers open on each panicle per day over a 6-10 week period from mid-spring. Berries follow, glossy purple-blue, 0.3-0.5 inch (8-12 mm) long, holding on the panicle for 8-12 weeks. Clumps expand 2-4 inches (5-10 cm) per year from short rhizomes, and several named forms send up shoots 12-24 inches (30-60 cm) from the parent. Leaves live 2-3 years and die from the tip down, leaving straw-colored ends that stay in the clump until pulled out. Foliage yellows in soil above pH 7.5, and clumps thin at the center after 5-7 years. Fruit of Dianella spp. species is recorded both as an Aboriginal food and as a cause of vomiting, and the compounds involved have not been identified.
Native Range
Native to eastern Australia, from northern Queensland south through New South Wales to eastern Victoria, with populations on Lord Howe Island. Grows in dry sclerophyll forest, coastal heath, and on sandstone slopes from sea level to 3,600 feet (1,100 m), usually in the understory beneath eucalypts. Several varieties are recognized across this range, differing in leaf width and in the length of the flowering panicle.Suggested Uses
Planted at 18-24 inch (45-60 cm) spacing in mass plantings, median strips, and understory beds in commercial landscapes across eastern Australia, and in mixed borders and coastal gardens in USDA zones 8-11. Grown in containers of 3 gallons (11 L) or larger, where clumps hold their form for 4-5 years before division. Grows under established trees in root-filled soil, though flowering drops off below 3 hours of direct sun.How to Identify
Appearance
Size & Dimensions
Height1' - 3'
Width/Spread1'6" - 3'
Reaches mature size in approximately 3 years
Colors
Bloom Information
Flowers open from mid-spring into early summer, September to December in eastern Australia and April to June in USDA zones 9-11 of the Northern Hemisphere. Only a few flowers on each panicle open on any one day, and the display runs 6-10 weeks. Individual flowers last one day and close by mid-afternoon. Berries color 6-8 weeks after flowering and stay on the stem into autumn.
Detailed Descriptions
Flower Description
Blue to violet with yellow anthersFoliage Description
Dark green to blue-greenGrowing Conditions
Sun Requirements
Requires 3-10 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
Water weekly for the first two growing seasons; established clumps hold their leaves through 4-6 weeks without water at temperatures below 90F (32C). Plants grow in full sun through about 50 percent shade, though leaves turn yellow-green and panicle numbers halve under deeper shade. Soils from sandy loam to clay loam at pH 5.5-7.0 are tolerated, and interveinal yellowing appears above pH 7.5. Dead leaves are pulled from the clump by hand each spring, since they do not shed on their own. Clumps thin at the center after 5-7 years and are lifted and split into sections of 3-5 fans in early spring. The silica-toothed leaf ridges cause shallow cuts to bare forearms during division.Pruning
Dead leaves and spent flower panicles are removed at the base once the berries have dropped, from late summer through autumn. Whole clumps are cut to 4-6 inches (10-15 cm) above ground level in early spring every 3-4 years; regrowth reaches full height in 10-14 weeks in warm climates and takes a full season in zones 8-9. Cutting during cold weather leaves the crown open to rot in wet soils. Hedge shears leave cut leaf tips that brown over the following 2-3 weeks.Pruning Schedule
J
F
M
A
M
J
J
A
S
O
N
D
early spring
Container Growing
✓ Suitable for container growing
Minimum container size: 3 gallons