perennial

Johnson's grass tree, Forest grass-tree, Steel grass

The Story

Plant Bio

Xanthorrhoea johnsonii, commonly known as Johnson's grass tree, is a slow-growing Australian perennial distinguished by its thick, fire-blackened trunk of resin-cemented leaf bases. This trunk is topped by a dense, symmetrical crown of narrow, arching green leaves that can take decades to reach mature height.

This species is distinguished by its non-glaucous, bright green leaves that are quadrate-rhombic in cross-section and strongly reflexed downward as they age. During the flowering season, it produces a massive, honey-scented cylindrical spike of creamy white flowers held aloft on a tall, woody scape.

Uses & Benefits:

Provides a dramatic, architectural focal point with its blackened trunk and symmetrical crown of fine, arching foliage.

Highly drought-tolerant and fire-resistant once established, making it ideal for low-maintenance and water-wise landscapes.

The nectar-rich flower spikes are highly valuable to native honeyeaters, bees, butterflies, and other beneficial insects.

Essentials

At a Glance

Plant Type

Perennial

Height

197 inches

Width

79 inches

Light

Full Sun, Partial Sun

Zones

9, 10

Water

Low

Humidity

Low to Moderate

Lifespan

Long-lived (centuries)

Native To

Eastern Australia

Toxicity

Non-toxic

Bloom period

Autumn – Spring

In flower about 7 months of the year

Planting

How to Grow

Select a planting site in full sun with exceptional drainage, such as a raised bed or a sandy, gravelly slope.
Excavate a hole twice as wide as the root ball but no deeper, taking extreme care not to disturb or bruise the delicate, fleshy black roots during transition.
Backfill with native soil or a sandy loam mix, ensuring the plant sits at the exact same depth as it did in its nursery container.
Water in thoroughly once to settle the soil, then withhold regular watering, allowing the soil to dry out completely between sessions.

Pro Tip

Protect the singular growing meristem at all costs; cutting back the green crown or pruning into old, leafless wood will permanently halt growth and kill the specimen.

Keep It Thriving

Care Guide

Do

Ensure flawless soil drainage to prevent root rot.
Leave dry, dead lower leaves intact as a natural protective skirt if desired.
Apply a low-phosphorus native-formulated fertiliser very sparingly if growth is sluggish.

Don't

Never overwater or allow the root zone to become waterlogged.
Do not shear or cut back the green foliage crown.
Never disturb the root ball or damage the fleshy contractile roots during planting.

Seasonal Care Calendar

Task	Jan	Feb	Mar	Apr	May	Jun	Jul	Aug	Sep	Oct	Nov	Dec
Fertilize
Mulch
Pest Check
Spring Cleanup

Watch Out For

Pests & Diseases

Common Pests

Common Diseases

In the Garden

Landscape Uses & Companions

Landscape Uses

Specimen plantingArchitectural featureNative gardensCoastal gardensRockeries

Companion Plants

Lomandra longifolia Anigozanthos flavidus Banksia spinulosa

Multiply

Propagation Methods

Good to Know

Common Questions

Johnson's grass tree, Forest grass-tree, Steel grass questions

What zones can Johnson's grass tree, Forest grass-tree, Steel grass grow in?

Johnson's grass tree, Forest grass-tree, Steel grass is hardy in USDA Zones 9–10. Inside that range it survives winter in the ground; outside it, grow it as an annual or a container plant you protect.

When does Johnson's grass tree, Forest grass-tree, Steel grass bloom?

Johnson's grass tree, Forest grass-tree, Steel grass typically blooms in autumn through spring. Exact timing shifts a week or two with your zone — Sow's bloom calendar maps it to your garden.

Does Johnson's grass tree, Forest grass-tree, Steel grass need full sun?

Johnson's grass tree, Forest grass-tree, Steel grass does best in full sun to part shade. In hot climates, afternoon shade keeps blooms fresher longer.

Is Johnson's grass tree, Forest grass-tree, Steel grass drought tolerant?

Yes — once established (usually after the first full season), Johnson's grass tree, Forest grass-tree, Steel grass handles dry spells with minimal watering. Water deeply its first year to build the root system that makes that possible.