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Acacia cognata

River wattle

Fabaceae

Southeastern Australia, Victoria and southern New South Wales

Attracts Pollinators Drought Tolerant Fragrant (light)Container Friendly

SunFull Sun – Part Shade

WaterMedium · drought-tolerant

HardinessZones 9–11

Overview

Acacia cognata is an evergreen large shrub or small tree 15-30 feet (4.5-9 m) tall and 10-20 feet (3-6 m) wide, with slender branchlets that arch out and hang, giving the crown a curtained outline. What appear to be leaves are phyllodes, flattened leaf stalks, narrow and linear at 1.5-4 inches (4-10 cm) long and 0.1-0.25 inch (2-6 mm) wide, slightly curved, bright to mid green, each with a single raised midvein and a resinous scent when crushed. Pale yellow to cream globular flower heads 0.2 inch (5 mm) across, each holding 15-25 individual flowers, open in short axillary racemes over four to six weeks in late winter and early spring. Flattened curved pods 2-4 inches (5-10 cm) long follow, browning and splitting to shed black seeds. The wood is brittle and long branchlets snap in strong wind. Along with most Australian Acacia spp., the species is damaged by phosphorus fertilisers at standard garden rates. Plants live 10-20 years and decline quickly at the end of that span. Hardy in USDA zones 9-11.

Native Range

Acacia cognata is native to southeastern Australia, in central and eastern Victoria and the far south of New South Wales. It grows along river banks, in gullies, and in moist sclerophyll forest, usually within reach of a watercourse, which is the source of the name river wattle. Plantings well outside that range depend on irrigation through summer.

Suggested Uses

Grown as a screening and shade tree in frost-free gardens, along creek lines and swales, and as a windbreak backdrop, spaced 12-15 feet (3.7-4.5 m) apart. The hanging branchlets are used against walls and over retaining structures where the foliage falls forward. Dwarf selections of the species are planted as low mounding groundcover and in containers of 15 gallons (57 L) or larger.

How to Identify

Branchlets hang rather than rise, and each carries narrow phyllodes under 0.25 inch (6 mm) wide with one raised central vein. Crushed phyllodes release a resinous scent. Flower heads are globular rather than cylindrical, cream to pale yellow rather than deep gold, and sit in short racemes of two to eight heads in the phyllode axils. A. floribunda overlaps in phyllode shape but carries cylindrical flower spikes, and A. subporosa has broader phyllodes with a gland set well above the phyllode base.

Appearance

Size & Dimensions

Height15' - 30'

Width/Spread10' - 20'

Reaches mature size in approximately 8 years

Colors

Flower Colors

Foliage Colors

Fall Foliage Colors

Bloom Information

Bloom Period

~5 weeks

Winter Spring

Flower heads open over four to six weeks, between August and October in the southern hemisphere and between February and April in northern hemisphere plantings. Colour is cream to pale yellow rather than the deep gold of many wattles, so the effect reads as a soft haze along the hanging branchlets. Flowers form on wood produced the previous season, and cutting the plant back hard in autumn removes that bloom. Native and introduced bees collect the pollen, which is the only reward, as the flowers hold no nectar.

Detailed Descriptions

Flower Description

Cream to pale yellow

Foliage Description

Bright to mid green narrow phyllodes with a single raised midvein

Growing Conditions

Sun Requirements

SunFull Sun SunPartial Shade

Requires 5-10 hours of direct sunlight daily

• Full Sun: 6+ hours of direct sunlight

• Partial Shade: 3-6 hours of direct sunlight

• Full Shade: Less than 3 hours of direct sunlight

Soil Requirements

pH Range5.5 - 7.0(Neutral)

357912

Soil Types

loam sand clay

Drainagewell drained

Water & Climate

Water Needs

Medium

Frost Tolerance

hardy

Time to Maturity

4-6 years to screening size, 8 years to full crown

Drought Tolerance

Drought tolerant when established

Care & Maintenance

Care Guide

Full sun to light shade with five or more hours of direct light produces the densest branchlet cover, and heavier shade opens the crown. The species grows in free-draining loam, sand, or drained clay at pH 5.5-7.0, and tolerates seasonally damp ground better than most wattles, matching its riverbank origin. Roughly 1 inch (2.5 cm) of water per week through the first two summers establishes the root system, after which the plant runs two to three weeks between waterings. Fertilisers containing phosphorus above about 3 percent damage the roots of Australian Acacia spp., so native-plant formulations or no feeding at all are what the species takes. A 3-inch (8 cm) mulch of coarse bark over the root zone, held clear of the trunk, holds moisture and moderates soil temperature. Sites sheltered from strong prevailing wind show less breakage of the long arching branchlets.

Pruning

Light tip cutting immediately after flowering holds the crown dense and keeps the plant within its space, taking no more than 10 percent of branchlet length at a time. Cutting into older bare wood produces no regrowth, since the species does not shoot readily from bare stems. Broken and dead branchlets are removed at their point of origin at any time of year. Hard reduction of a mature plant leads to dieback rather than renewal.

Pruning Schedule

late spring