Complete seed propagation guide by TOMs FLOWer CLUB

General background: What is Brachychiton populneus?

Brachychiton populneus, commonly known as the Kurrajong or Bottle Tree, is an evergreen to semi-evergreen tree native to Australia. It is prized for its sculptural, thickened trunk, leathery green leaves, and excellent drought tolerance. In cultivation, Brachychiton populneus is suitable both as a garden tree in mild climates and as a container-grown plant when young.

The species grows slowly to moderately and develops a strong root system early on. This makes seed propagation especially rewarding for patient growers who value robust, long-lived plants grown naturally.

Why propagate Brachychiton populneus from seed?

Seed propagation is the most reliable and natural method to grow healthy Brachychiton populneus. Seed-grown plants:

• develop stronger root systems

• show higher long-term resilience

• adapt better to local growing conditions

While leaf shape and growth vigor may vary slightly, the essential characteristics of the species remain stable.

Understanding Brachychiton seeds

After flowering, Brachychiton populneus produces woody, boat-shaped seed pods. Once mature, these pods split open and release numerous dark seeds covered in fine, irritating hairs.

Good to know: Always wear gloves when handling seeds or pods. The hairs can irritate skin and respiratory passages.

Cleaned seeds store well in a dry, cool place and remain viable for several years.

Best time to sow Brachychiton seeds

The optimal sowing period is spring to early summer.

Ideal germination conditions:

• Soil temperature: 20–25 °C

• Bright location with indirect light

• Frost-free environment

Indoor sowing or a greenhouse setup significantly improves germination success.

Step-by-step guide: How to propagate Brachychiton populneus from seeds

1. Seed preparation

Soak seeds in lukewarm water for 12–24 hours to soften the seed coat and promote even germination.

2. Substrate selection

Use a very well-drained, airy substrate.

Recommended mix (TOMs FLOWer CLUB):

• 50% mineral components (pumice, perlite, sand, or fine gravel)

• 50% high-quality organic soil or coco fiber

The substrate should retain slight moisture but never stay wet.

3. Sowing the seeds

• Place seeds horizontally on the substrate

• Cover lightly with 5–10 mm of soil

• Water gently to settle the mix

4. Germination phase

• Keep evenly moist, never soggy

• Maintain warmth and good airflow

Germination usually occurs within 2–4 weeks, though some seeds may take longer.

Seedling care after germination

Once seedlings appear:

• Move to a very bright location, avoiding strong direct sun initially

• Allow the substrate to dry slightly between watering

• Do not fertilize for the first 6–8 weeks

Because seedlings form a taproot early, deep pots are preferable.

Potting on and further cultivation

When seedlings reach 10–15 cm in height:

• Pot individually into deeper containers

• Use the same well-drained substrate

• Handle roots carefully to avoid taproot damage

Repotting is usually only required every 1–2 years.

Tips & hints for successful cultivation

• Less water is better than too much

• Drainage is essential at all stages

• Gradually acclimate young plants to sun

• Avoid cold, wet conditions, especially in winter

Good to know about Brachychiton populneus

• Juvenile and adult leaves can look very different

• Trunk thickening develops slowly and naturally

• Seed-grown plants are typically stronger than cuttings

• Ideal for growers who enjoy long-term plant development