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How to Grow Grass Tree

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Grass Tree

Xanthorhea

shrub

Xanthorhea, commonly known as grass trees or blackboys, are distinctive Australian plants characterized by a thick, trunk-like stem topped with a dense crown of long, narrow leaves. These slow-growing evergreen plants can live for centuries and produce tall, striking flower spikes. They are prized ornamental plants that add dramatic architectural interest to gardens and landscapes.

Looking for a specific variety?

Xanthorhea australis Xanthorhea preissii Xanthorhea minor Xanthorhea johnsonii Xanthorhea pumila

When should you plant Grass Tree in your zone?

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Example Grass Tree timeline · Pittsburgh, PA (Zone 6b)

  1. Plant Grass Tree

    Around Apr 17

    Near Pittsburgh's average last spring frost.

  2. Tend & protect

    Late spring–summer

    Watering, feeding, and pest-watch reminders.

  3. Harvest Grass Tree

    Late summer into fall

    Before the first fall frost (≈ Nov 8)

Sample dates for Pittsburgh, PA. Sign up to get exact Grass Tree dates for your own zip code.

Growing Conditions

☀️
Sun: Full sun to partial shade; 6+ hours of direct sunlight daily
💧
Water: Drought tolerant once established. Water moderately during growing season; reduce in winter. Avoid waterlogging at all costs. Prefer dry conditions over wet.
📏
Spacing: 36-60 inches
📅
Days to maturity: Not applicable; slow-growing, takes 10-15 years to develop characteristic trunk
🌱
Planting depth: Plant at soil level; do not bury the crown

Soil

Type: Sandy, well-draining loamy soil with low fertility
pH: 6.0-7.0
Amendments:
Coarse sand Perlite Gravel Minimal organic matter

Growing Zones

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Thrives in zones 9-11; best in Mediterranean and subtropical climates

9a 9b 10a 10b 11a 11b

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Growth Stages

1

Establishment (Years 1-3)

1-3 years

Plant develops root system and slowly produces rosette of leaves. Little visible above-ground growth.

Keep soil moist but not wet during establishment. Protect from frost. Avoid disturbance. Do not fertilize.

2

Vegetative Growth (Years 3-10)

5-10 years

Gradual thickening of stem base and expansion of leaf crown. Plant develops characteristic form.

Maintain well-drained conditions. Minimal watering needed once rooted. No pruning required. Protect in harsh winters.

3

Maturation (Years 10+)

Ongoing

Distinct trunk develops, creating the iconic silhouette. Plant achieves mature height and form.

Maintain excellent drainage. Water only during severe droughts. Remove any dead leaves from crown base.

4

Flowering

2-4 weeks

Tall, dense flower spikes emerge from crown center, appearing white, cream, or yellowish depending on species.

Flowers attract pollinators. Allow spikes to develop fully. No special care needed.

5

Seed Production

Several months

Flower spikes mature and develop seed capsules. Spikes persist for extended period.

Seeds are viable and can be collected for propagation. Spikes eventually dry and can be removed.

Companion Planting

Plan your garden →

Plant with:

Banksia Bottlebrush Desert rose Agapanthus Lavender Rosemary Ornamental grasses Kangaroo paw

Avoid planting near:

Moisture-loving plants Aggressive root systems Nitrogen-fixing legumes in moist conditions

Common Pests

  • Ensure excellent drainage; avoid overwatering; use well-draining potting mix; improve air circulation; remove affected plants if necessary

  • Spray with insecticidal soap; prune infested leaves; improve air circulation; monitor regularly

  • Spray with water to dislodge; use neem oil if severe; ensure adequate humidity without waterlogging

  • Remove manually; spray with horticultural oil; prune heavily infested stems

Uses

🌿

Striking Landscape Feature

Ornamental

Xanthorhea serves as a dramatic focal point in gardens, particularly in Mediterranean, drought-tolerant, and xeriscaping designs. Its distinctive architectural form provides year-round visual interest. [source]

🦋

Pollinator Nectar Source

Wildlife

The tall flower spikes attract native bees, birds, and other pollinators, supporting local ecosystems. Flowering provides important nectar during specific seasons. [source]

🏠

Resin and Traditional Uses

Household

Historically, Aboriginal peoples extracted resin from the trunk base for use as a waterproofing agent and adhesive. Early European colonists also used the resin for various purposes. [source]

🎨

Dried Flower Arrangements

Craft

Mature flower spikes can be dried for use in decorative arrangements and floral designs, providing unique dried botanical elements. [source]

🍳

Honey Production Source

Culinary

In native regions, Xanthorhea flowers support native bee populations that produce distinctive floral honey products. [source]

Harvest Tips

Xanthorhea is not harvested for food. Historically, resinous material from the stem base was used. Seeds can be collected after flowers mature and dry. Allow seedheads to fully develop before harvesting seeds.

Fun Facts

  • 🌱 Xanthorhea plants can live for over 300 years, making them among the longest-living plants in Australia. Some individual specimens are believed to be over 600 years old.
  • 🌱 The common name 'blackboy' derives from the black, charred appearance of the trunk following bushfires—the plant is highly fire-resistant and often survives fires that destroy surrounding vegetation.
  • 🌱 Despite their grass-like appearance, Xanthorhea are not grasses at all but rather monocots related to lilies and belong to the family Xanthorrhoeaceae. The name comes from Greek words meaning 'yellow' and 'resin.'

Gardening Terms

New to gardening? Learn about terms used in this guide:

Crown Full Sun Partial Shade
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