Why slopes erode

Erosion is simply soil moving faster than it's being held. On a slope, gravity, water and bare ground work together — and the steeper and longer the slope, the more energy the runoff carries. The forms of water erosion escalate in stages:

• Splash / raindrop erosion — raindrops hit bare soil, detach particles and seal the surface, cutting infiltration.
• Sheet erosion — a thin, even layer of topsoil is peeled off across the whole slope; easy to miss until the topsoil is gone.
• Rill erosion — runoff concentrates into small channels you could step over; the sign water is gaining power.
• Gully erosion — rills deepen into channels too big to drive across or rake away; expensive to repair.
• Tunnel erosion — water moves through dispersive (sodic) subsoil and collapses into gullies later (see Step 2).

Four factors decide how bad it gets: rainfall intensity, slope gradient and length, soil erodibility (dispersive/sodic and silty soils are worst), and ground cover — the factor you control most. Erosion drops sharply once living and dead cover exceeds roughly 70%.

How plants actually control erosion

Vegetation isn't decoration here — each layer does mechanical work.

Step 1 — Assess the site

Ten minutes of assessment saves a season of failed plants. Slope is described three ways; matting ratings use the ratio (horizontal : vertical — "3:1" means 3 m across for every 1 m of drop):

Then check five things

• Soil type & dispersion — test for dispersive (sodic) soil: drop an air-dry crumb into a glass of clear water; a milky halo means it's dispersive and needs gypsum + fast cover.
• Where the water comes from — walk uphill; concentrated runoff arriving from above will destroy new plantings unless intercepted.
• Aspect & exposure — hot north/west faces dry fast (choose tough species); wind and salt narrow the list.
• Existing vegetation — keep every established plant you can; its roots already hold the slope.
• Access & safety — anything steeper than ~2:1 is hazardous; plan access and never work directly below loosened soil.

Step 2 — Prepare the site

Preparation is where erosion jobs are won or lost. Sequence: water, shape, soil, weeds, armour.

a. Control the water first

Before anything else, divert runoff arriving from above the slope with a contour bank, catch drain or diversion drain across the top, leading to a stable, vegetated outlet. Never let concentrated flow spill onto a slope you're trying to establish.

b. Reshape to a stable angle

The most effective structural fix is to batter the slope back to a gentler gradient — aim for 2:1 or flatter, ideally 3:1. On tall or space-limited slopes, cut benches or terraces to break the slope length (shorter slopes = less runoff energy), each draining to a safe outlet.

c. Loosen the surface

Rip or scarify along the contour (never up-and-down, which creates drainage lines), respread stripped topsoil, and leave a roughened, stepped surface that catches seed, water and mulch.

d. Kill the weeds now

Pre-plant weed control is the most under-rated step — weeds outcompete natives and are far harder to remove later. Where appropriate, use a registered herbicide and follow the label (check actives, rates and withholding on Spray Hub).

e. Armour steeper slopes with matting

On steep, high-risk or concentrated-flow slopes, install a biodegradable erosion-control blanket to hold soil and seed until plants take over. Match product to slope:

Step 3 — Choose the right plants

Good erosion plantings are layered communities, not one species. Five principles:

1. Local provenance — species indigenous to your area, ideally from local seed; adapted and won't become weeds.
2. Layer the community — groundcovers + tussock/strappy plants & native grasses + shrubs + trees.
3. Speed + depth — quick coverers for the first season, deep-rooted anchors for the long term.
4. Match the microsite — moisture, drainage, aspect, salt and shade; a wet creek toe is not a hot dry crest.
5. Never introduce a weed — avoid vigorous exotics (and some non-local natives); check your state weed list.

Native plant selection by climate zone

Build a community for your zone by picking across the layers (groundcover, grass/strappy, shrub, tree). Confirm the locally-indigenous species with a native nursery or catchment authority.

Tropical & wet-dry tropics — Nth QLD, NT Top End, Nth WA

Subtropical / warm-temperate — SE QLD, coastal NSW

Cool temperate — VIC, TAS, southern NSW, ACT, tablelands

Mediterranean — SW WA, southern SA (wet winter / dry summer)

Semi-arid & arid — inland

Step 4 — Plant it effectively

Timing — plant into moisture

Plant after rain, into moist soil. Best windows across most of Australia: autumn (roughly Feb–April) ahead of winter rain, and spring after frost risk. In the seasonal tropics, plant into the early wet season. Avoid young or actively-growing stock in cold winter or summer heat.

Method — match to scale

Layout & density

Plant along the contour in staggered/offset rows so no continuous up-and-down gap channels water. Go dense — close spacing gives quick cover, shades out weeds and creates a sheltered micro-climate. Layer groundcovers and grasses between and beneath shrubs and trees.

Planting technique

1. Dig a hole twice the tube width; tease out circling roots.
2. Plant at soil level, backfill and firm in to remove air pockets.
3. Form a small basin/lip on the downhill side to catch water.
4. Water in immediately — even in wet weather — to settle soil around roots.
5. Mulch around (not against) the stem.

Step 5 — Establish & maintain

The first 1–3 years decide whether the slope is fixed for good; most failures happen here, from neglect.

Monitor & top up

• Set up photo-points and re-shoot the same angles each season to track cover and spot rills early.
• Infill and replace failed plants promptly — gaps are where erosion restarts.
• Check matting and pins after big storms; re-pin lifted edges.
• Once cover exceeds ~70% and plants are self-supporting, the matting has done its job and breaks down naturally.
• Only take on the area you can realistically maintain.

Common mistakes that undo the job

• Ignoring water from above — the fastest way to lose a new planting.
• Planting too sparsely — slow cover means weeds win and soil keeps moving.
• Exposing dispersive subsoil and leaving it bare — invites rilling and tunnel erosion.
• Skipping pre-plant weed control — the single most common cause of failure.
• Planting in the wrong season without follow-up water.
• Using weedy exotics for "quick cover" — a new problem that spreads off-site.
• Poor matting install — no anchor trench, air gaps, or reversed overlaps.
• Fertilising natives (especially with phosphorus) and killing P-sensitive species.
• No maintenance — walking away after planting.

Legal & safety

• Native vegetation & clearing rules — clearing existing native vegetation (even to "tidy up" a slope) is regulated in every state/territory and may need approval. Check with your council or state environment/planning body before removing vegetation.
• Waterways & riparian works — works on or near creeks, drainage lines and banks may require a permit (state water/environment authority). Riparian zones have their own rules and often their own funding/support.
• Weed hygiene — clean machinery, boots and tools between sites to avoid spreading weed seed and pathogens (e.g. Phytophthora). Source clean, local-provenance stock.
• Chemical use & records — only use herbicides registered (or permitted) for the situation, follow the label, and keep the spray records your state requires for commercial application.
• Working safely on slopes — steep batters are a fall and machinery-rollover hazard. Plan access, work top-down where possible, and never stand directly below loosened soil or operating machinery.

Plants, seed & where to source them

Match sourcing to method and always favour local provenance.

• Tubestock & groundcovers — local native, Landcare/community and council revegetation nurseries (best for local-provenance stock).
• Native seed & seed mixes — specialist suppliers such as Australian Seed (australianseed.com), which stocks native grasses, Lomandra, Juncus and Baumea, groundcovers, saltbush (Atriplex) and bluebush (Maireana) for harsh sites, wattles (Acacia), and offers seed pre-treatment (including smoke) to lift germination. Ideal for hydroseeding and direct seeding at scale.
• Advice & local species lists — your regional Landcare group, catchment/NRM body, Greening Australia, Local Land Services and council revegetation guides can confirm the right indigenous species and provenance for your exact area.
• Chemicals for pre-plant weed control — check actives, rates and withholding periods on Spray Hub and always follow the label.

References & further reading

Ozbreed — Top 10 Erosion Control Plants by State · Land for Wildlife SEQ — Revegetation Principles · Fernland — Coir vs Jute for Erosion Control · IECA Australasia — Best Practice Erosion & Sediment Control · NRE Tasmania — Dispersive Soils & Tunnel Erosion · Agriculture Victoria — Tunnel erosion remediation · Landscape SA — Revegetation fact sheets · Australian Seed.

Frequently asked questions