Why Underplant Crepe Myrtles?
Crepe myrtles (Lagerstroemia spp.) are a favourite in Australian gardens for their vibrant summer blooms, striking bark and graceful vase-shaped canopy. Thriving in warm temperate to subtropical climates (ideal for coastal NSW, QLD and northern VIC), they cast dappled shade that creates a perfect microclimate for understory planting. Underplanting not only fills bare soil but suppresses weeds, retains moisture, attracts pollinators and adds year-round interest.
Choosing the right companions is key. Crepe myrtles prefer free-draining soil, full sun to part shade and moderate watering once established. Their roots are non-invasive, so pair them with drought-tolerant, shade-adapted plants that handle dry spells and summer heat. In cooler southern regions like Melbourne or Adelaide (frost zones 2-4), opt for hardier options.
Key Considerations for Underplanting
Before selecting plants, assess your site:
- Light: Dappled shade under the canopy; avoid deep shade lovers.
- Soil: Well-drained, slightly acidic to neutral (pH 5.5-7). Amend clay soils with compost and gypsum.
- Water: Low to moderate; mulch 5-7 cm deep to conserve moisture.
- Climate: Subtropical (Brisbane): heat-lovers. Temperate (Sydney): versatile. Arid (Perth): ultra drought-tolerant.
- Spacing: Plant 30-50 cm apart; keep 1-2 m clear around the trunk.
Prepare by removing turf, forking in organic matter and applying slow-release fertiliser (e.g., native mix, 100 g/m²).
Best Groundcovers for Under Crepe Myrtle
Groundcovers form a living carpet, ideal for weed suppression and erosion control.
Native Aussie Stars
- Myoporum parvifolium (‘Fine Leaf’ or ‘Putah Anangu’): Tough as nails in full sun to shade. Pink/white flowers spring-summer. Grows 10-15 cm high, spreads 1-2 m. Perfect for arid and coastal gardens; tolerates -5°C. Plant in 20 cm pots, space 50 cm.
- Scaevola aemula (Fairy Fan Flower): Prostrate form trails beautifully. Lavender-blue flowers year-round in warm areas. Drought-hardy, 20 cm high, 1 m spread. Suits Sydney to Perth; attracts butterflies.
- Brachyscome multifida (Cut-leaf Daisy): Fine foliage, mauve daisy flowers. 15 cm high, 50 cm spread. Shade-tolerant, frost to -7°C. Great for cool climates like Tasmania.
Exotic Options
- Mondo Grass (Ophiopogon japonicus): Glossy strappy leaves, 20-30 cm high. Thrives in dappled shade; slow-growing, low-maintenance. Black berries add interest.
- Liriope muscari: Purple flower spikes summer. 30 cm high, clumping. Handles dry shade; divide every 3 years.
These spread gently without competing aggressively with crepe myrtle roots.
Top Perennials and Strappy Plants
Perennials add height (30-60 cm) and seasonal colour without overwhelming the tree.
- Dianella caerulea (Blue Flax Lily): Native superstar. Strappy blue-green leaves, blue berries. 50 cm high. Shade to sun, drought-tolerant once established. Fruits attract birds; suits all Aus climates.
- Lomandra hystrix (‘Lime Tuff’): Lime-green lime tufts, 60 cm high. Ultra-tough; wind, salt and frost resistant (-10°C). Perfumes lightly in spring.
- Viola hederacea (Native Violet): Delicate purple/white flowers. Creeping, 10 cm high. Loves moist shade; groundcover for humid subtropics like Gold Coast.
- Geranium ‘Rozanne’: Exotic cranesbill with violet-blue flowers June-November. 45 cm high, spreads 60 cm. Long-blooming, slug-resistant.
In tropical QLD, try Cordyline fruticosa dwarfs for colourful foliage accents.
Small Shrubs and Bulbs for Added Drama
For vertical interest up to 1 m:
Shrubs
- Grevillea ‘Poorinda Constance’: Low-growing (80 cm), red toothbrush flowers. Attracts honeyeaters; dry shade tolerant.
- Westringia fruticosa (‘Zig Zag’ or dwarf): Grey foliage, white flowers. 50 cm high, coastal hardy.
Bulbs and Tubes
- Watsonia hybrids: Strappy leaves, red/pink spikes spring. 60 cm high. Plant corms 10 cm deep; lift in wet tropics.
- Crinum pedunculatum (Swamp Lily): Native, fragrant white flowers. 1 m high. Tolerates periodic wet; coastal NSW/QLD.
Avoid thirsty bulbs like agapanthus if drainage is poor.
Planting and Maintenance Tips
Step-by-Step Planting
- Timing: Autumn-winter in south, early spring north.
- Prep: Water crepe myrtle deeply; mulch existing plants aside.
- Plant: Dig holes twice pot width, same depth. Backfill with native soil mix.
- Water: 10-20 L/week first summer; taper off.
- Mulch: 5 cm sugar cane or lucerne around plants, not touching stems.
Ongoing Care
- Fertiliser: Low-phosphorus native blend (e.g., Yates Native GT) in spring. 50 g/m².
- Pruning: Tip-prune perennials post-flower; groundcovers self-regulate.
- Pests: Watch for aphids on new growth; hose off or neem oil.
- Weeds: Hand-pull initially; mulch prevents regrowth.
In arid zones, install drip irrigation (2 L/hour, 2x/week summer).
Climate-Specific Recommendations
| Climate Zone | Top Picks |
|---|---|
| Subtropical (Brisbane, Gold Coast) | Scaevola, Dianella, Viola hederacea, Crinum |
| Temperate (Sydney, Melbourne) | Myoporum, Lomandra, Brachyscome, Geranium |
| Arid (Perth, Adelaide) | Myoporum ‘Putah Anangu’, Westringia, Liriope |
| Cool (Tasmania, highlands) | Mondo Grass, Viola banksii, Lomandra ‘Katrinus Deluxe’ |
Common Mistakes to Avoid
- Overwatering: Leads to root rot in both tree and companions.
- Heavy Feeders: Skip roses or delphiniums; they compete.
- Invasive Spreaders: No mint or ivy; they smother.
- Ignoring Scale: Tall plants block crepe myrtle’s base.
Design Ideas for Impact
- Monochrome: White-flowering Scaevola + Lomandra under white crepe myrtle.
- Colour Pop: Purple Dianella + red Watsonia beneath pink-flowered L. indica.
- Textural Mix: Strappy Lomandra + fine Myoporum + bold Cordyline.
- Edible Edge: Native violets (edible flowers) + warrigal greens for permaculture.
Underplanting transforms crepe myrtles from feature trees into layered spectacles. Start small, observe and expand. Your garden will thank you with low-maintenance beauty year-round.
(Word count: 1,128)