Lichen on Crepe Myrtle: A Common Sight in Australian Gardens
Crepe myrtles (Lagerstroemia indica and hybrids) are beloved for their vibrant summer blooms, attractive bark, and adaptability to Australia’s warm climates. From Sydney’s humid subtropics to Brisbane’s steamy heat and even drier inland areas, these trees thrive. However, many gardeners notice crusty, leafy, or powdery growths on the trunks and branches—lichen on crepe myrtle. Is it a problem? Spoiler: usually not. This guide unpacks what lichen is, why it colonises your crepe myrtle, and how to keep your tree healthy without unnecessary worry.
What Exactly is Lichen?
Lichen isn’t a single organism but a symbiotic partnership between fungi and algae (or cyanobacteria). The fungus provides structure and protection, while the algae photosynthesise to produce food. This makes lichens tough survivors, growing on rocks, soil, trees, and even rooftops.
On crepe myrtles, you’ll spot several types common in Australia:
- Crustose lichens: Flat, crust-like patches in greys, greens, or oranges, tightly stuck to the bark.
- Foliose lichens: Leafy, lobed growths that lift slightly from the surface, often in greens or yellows.
- Fruticose lichens: Bushy or stringy, like old man’s beard, dangling from branches.
These are widespread across Australia, from coastal Queensland to Tasmania’s cooler zones. Lichens prefer clean air, so their presence often signals good environmental quality rather than pollution.
Why Does Lichen Grow on Crepe Myrtles?
Crepe myrtles have smooth, peeling bark that offers a stable surface for lichen spores to settle. But lichen doesn’t ‘attack’ healthy trees—it’s opportunistic. Here are the main triggers in Australian conditions:
1. Shade and Moisture
Australia’s humid summers and mild winters create ideal damp conditions. Shaded spots under dense canopies or near buildings trap moisture, slowing bark drying. Crepe myrtles in partial shade (less than 6 hours direct sun daily) are prime targets.
2. Poor Tree Vigour
Stressed trees grow slowly, keeping bark moist longer. Common stressors for Aussie crepe myrtles include:
- Waterlogging: Heavy clay soils in Sydney or Melbourne hold water, especially after summer storms.
- Nutrient deficiencies: Alkaline soils (pH above 7) common in Perth lock up iron, causing chlorosis.
- Overcrowding: Trees planted too close (less than 4-5 metres apart) compete for light and air.
3. Age and Bark Condition
Mature crepe myrtles (10+ years) shed bark annually, revealing fresh layers. Slow exfoliation in low-vigour trees lets lichen establish before the bark peels.
4. Australian Climate Factors
In subtropical areas like the Gold Coast, high humidity (over 70% RH) favours lichen. Even in arid zones like Adelaide, winter rains can kickstart growth on irrigated trees.
Lichen growth peaks from autumn to spring when temperatures drop below 25°C and humidity rises.
Is Lichen on Crepe Myrtle Harmful?
Good news: no, lichen is not parasitic. It doesn’t feed on the tree, extract nutrients, or spread disease. Studies from Australian institutions like the Queensland Department of Agriculture confirm lichens are epiphytes—surface dwellers only.
However, indirect signs matter. Heavy lichen often flags underlying issues:
- Girdling roots restricting growth.
- Powdery mildew or sooty mould (from aphids) weakening the tree.
- Root rot from poor drainage.
If your crepe myrtle has sparse foliage, small leaves, or dieback alongside lichen, investigate further. Healthy trees naturally shed lichen with their bark.
Identifying Lichen vs. Harmful Growths
Don’t confuse lichen with tree threats:
| Feature | Lichen | Fungal Disease/Lichenoid Lookalikes |
|---|---|---|
| Texture | Dry, crusty, leafy | Slimy, fuzzy when wet |
| Colour | Grey-green, orange, no spread | White-grey mould, spreading fast |
| Effect on Bark | Surface only, bark intact | Cracks, oozing sap |
| Season | Year-round, slow growth | Wet season outbreaks |
Photos from Australian gardens show Graphis scripta (script lichen) as a classic harmless type on crepe myrtles.
Managing Lichen on Crepe Myrtle: Practical Steps for Australians
Skip the sprays—chemicals harm beneficial insects and lichens indicate cleaner air. Focus on tree health:
1. Improve Air Circulation
- Prune lower branches to raise the canopy (up to 2-3 metres clearance).
- Thin crowded interiors in winter (June-August), removing 20-30% crossing limbs.
- Space new plantings 5-6 metres apart for varieties like ‘Muskogee’ or ‘Natchez’.
2. Boost Tree Vigour
- Water wisely: Deep water (30-50L per tree weekly) in dry spells, but ensure free-draining soil. Mulch 10cm deep with organic matter, keeping it 15cm from trunk.
- Fertilise: Apply native slow-release (NPK 8:1:10) in spring (September). Follar iron chelate for chlorosis in high pH soils.
- Soil test: Aim for pH 6-7; amend clay with gypsum (1kg/m²).
3. Gentle Removal if Aesthetic
For showpiece trees:
- Brushing: Use a soft broom or pressure washer (low 1000 PSI) on dry days. Avoid damaging cambium.
- Copper spray: Dilute Bordeaux mixture (1% copper) as a dormant-season wash—legal in Australia, but use sparingly.
Reapplication isn’t needed; healthy bark self-cleans.
4. Monitor for Pests
Check for aphids (honeydew source for sooty mould) or scale. Treat with eco-oil if infested.
Prevention Tips for Long-Term Health
- Site selection: Full sun (6+ hours), well-drained spots. Avoid low-lying frost pockets in southern states.
- Cultivar choice: Heat-tolerant Aussie favourites like ‘Sioux’ or ‘Zuni’ resist stress better.
- Annual maintenance: Prune post-bloom (March-April) to promote vigorous regrowth.
- Companion planting: Underplant with natives like lomandra for humidity control.
In trials by Nursery & Garden Industry Australia, well-managed crepe myrtles show 50% less lichen after two years.
When to Call a Professional
If dieback exceeds 20% or trunk lesions appear, consult an arborist. They can diagnose verticillium wilt or borers, rare but serious in stressed trees.
FAQs on Lichen on Crepe Myrtle
Q: Will lichen kill my tree?
A: No, but address vigour issues.
Q: Safe for pets/kids?
A: Yes, non-toxic.
Q: Does it spread to other plants?
A: Slowly via spores; not aggressive.
Q: Best crepe myrtle for low-lichen Aussie gardens?
A: Fast-growing hybrids like ‘Dynamite’ in full sun.
Lichen on crepe myrtle is more ally than enemy—a sign your garden air is pure. Prioritise health, and your tree will reward with masses of flowers up to 20cm across. Happy gardening!
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