Swamp banksia

Sun

Full sun to light shade; flowering is usually best in sun.

Water

Moderate to high. Keep young plants consistently moist; established shrubs tolerate short dry periods but perform best with reliable moisture.

Soil

Acidic, low-phosphorus sand or sandy loam, including seasonally waterlogged ground. Avoid alkaline soil and permanently stagnant conditions.

Height

6-10 ft (1.8-3 m)

Spread

6-10 ft (1.8-3 m)

Flowers

Usually late summer through winter, though timing varies with climate and flowers can appear outside this period. Upright spikes open green-blue, turn yellow-green to yellow, then age brown.

Foliage

Evergreen. Large, broad, leathery green leaves with toothed edges and pale, hairy undersides; young growth is often rusty brown.

Growth

Moderate

Care needed

Medium

• Pollinators
• Heat tolerant
• Wildlife
• Low allergen

Northern hemisphere months. In Australia, shift them by six.

Difficulty

Hard

Toughness

Fairly tough

Pick your zone, country, light and whether you have pets.

1. Planting day

   1.6 ft (0.5 m)

2. After 1 year

   2.9 ft (0.88 m)

3. After 2 years

   4 ft (1.3 m)

4. After 3 years

   5 ft (1.6 m)

5. After 5 years

   8 ft (2.4 m)

   full size

About 5 years to full size.

From a typical nursery size, at an average rate for this kind of plant. A rule of thumb, not a forecast.

Cats and dogs

Safe

Native to

Australia

Growth rate

Moderate

• Water deeply during establishment and through prolonged dry weather; do not let a container root ball dry out completely.
• Feed sparingly, using only a low-phosphorus fertiliser labelled suitable for Australian native plants.
• Spread a light layer of coarse organic mulch over the root zone, keeping it clear of the stems.
• Avoid digging around the shallow roots or adding manure and rich general-purpose fertilisers.
• Shelter young plants from frost and cold winds; grow in a movable container where winters are too cold.

Pruning. After the main flowering period, lightly shorten leafy shoots to encourage branching and remove dead or damaged wood. Avoid routine hard pruning into bare old wood; although this species can reshoot from its woody base, recovery is not guaranteed in garden conditions.

Spring

Plant after frost risk has passed in cooler districts, watering the root ball thoroughly.

Spring

Refresh mulch and, only if growth is weak, apply a small amount of low-phosphorus native-plant fertiliser.

Summer

Check soil moisture during hot spells and water deeply before the root zone dries out.

Late summer

Inspect developing flower spikes and young shoots for scale insects and honeydew.

Autumn

Plant in mild, frost-free districts while the soil is still warm; keep new plants moist.

Winter

Protect young shrubs from forecast frost and move container plants under bright, frost-free cover where necessary.

• Use as a bold-leaved specimen beside a path or patio, leaving room for its broad mature shape.
• Plant along the upper edge of a rain garden where soil is moist but water does not remain stagnant.
• Combine with sedges and other moisture-loving Australian natives for contrasting leaf shapes.
• Include in a sunny wildlife border where nectar-feeding birds can reach the flowers.

Garden styles it suits: Australian native, Architectural minimal, Wildlife garden, Coastal, Bog garden and Modern tropical.

Plant it with: Swamp bottlebrush, Swamp paperbark, Knobby club-rush, Tall sedge and Flax-leaf paperbark.

Wildlife: The nectar-rich flowers attract honeyeaters in Australia and other nectar-feeding birds and insects where grown. Woody seed cones can provide food for seed-eating birds.

• Yellow leaves in alkaline soil: test soil pH and use a suitable acidic planting site or an acidic, low-phosphorus container mix rather than repeatedly adding fertiliser.
• Phosphorus toxicity, causing scorched leaves and declining growth: stop general-purpose feeding and avoid manure; use only products suitable for phosphorus-sensitive natives.
• Root rot, including Phytophthora, can cause sudden wilt and dieback: avoid contaminated soil and stagnant conditions, and remove badly affected plants.
• Scale insects can cause sticky honeydew and sooty mould: inspect stems and leaf undersides, remove small infestations by hand and use a labelled horticultural oil if needed.

Not known to be toxic to people, cats, dogs or horses. No particular part is recognised as poisonous, but species-specific safety information is limited; discourage pets and children from chewing leaves or woody cones.

• Saw banksia (Banksia serrata)

  Usually develops rough, corky bark and a more tree-like form. Its leaves are generally narrower, while swamp banksia has especially broad leaves and smoother young stems.

• Fern-leaved banksia (Banksia oblongifolia)

  Has smaller, narrower leaves and rusty-hairy young shoots. Swamp banksia has much larger, broader leaves with a conspicuously pale underside.

Banksia honours botanist Joseph Banks, while robur is Latin for strength or oak, referring to the sturdy, oak-like leaves; swamp banksia describes its naturally wet habitat.

Propagation. Usually grown from seed sown in a free-draining, low-phosphorus propagation mix and kept moist in a warm, bright place. Collect seed from mature woody cones that open naturally; semi-ripe cuttings are possible but can be difficult to root.

Accepted botanical name

Banksia robur

Native range

New South Wales and Queensland.

Measured

Average height 185 cm.

Sources: GBIF (CC BY 4.0) and Trefle (CC BY 4.0). The care and design notes are LandscapeGPT's own.