Introduction
Are you struggling with erosion on a sloped garden but want to maintain your hedges and screens? It can be distressing to see the roots of your hedges and screens exposed due to eroding soil, because this is a quick way to invite plant health problems and even plant death.
Managing a sloped garden presents unique challenges, particularly regarding soil erosion, water runoff, and plant stability. To make life even harder, one of the most efficient methods of erosion control, mulching, is much more difficult because mulch tends to roll down the slope instead of staying in place, causing unwanted mess and a potential tripping hazard at the base of the slope and eventually leaving the ground uncovered.
Thoughtful planning and practical solutions can prevent erosion and ensure the health of your plants. This article will guide you through effective strategies to manage slopes and support your hedges and screens.
Exposed roots are a sign of erosion, which is common on slopes. We can never turn back time and prevent erosion that’s occurred – all we can do is prevent the problem getting worse using soil amendments and ground-covering mulches and plants. https://www.flickr.com/photos/your_teacher/4293328993
The Basics of Slope Management
Understanding Slope Challenges
Slopes come with their own set of challenges. Soil erosion is a significant concern, as gravity pulls the soil and mulch downward, especially during heavy rainfall. This process strips away the nutrient-rich topsoil essential for plant growth, and can potentially expose roots that were once buried.
Water runoff and high winds also lead to excessive loss of soil and nutrients on a slope, which can damage both the landscape and plants. Ensuring plant stability is crucial because plants on slopes need strong root systems to anchor themselves and prevent being dislodged by erosion or water runoff.
Importance of Proper Planning
Proper planning is vital for managing slopes effectively. Start by assessing the slope’s steepness to decide the best erosion control methods. Gentle slopes may require less intensive measures compared to steep ones.
Evaluate your soil type to understand its susceptibility to erosion, as this helps in selecting appropriate plants and soil amendments. Additionally, consider sunlight and wind exposure to choose suitable plant species (including hedges and ground covers) that will thrive under those specific conditions.
Erosion Control Strategies
Effective erosion control is vital to maintaining slope stability.
Mulching on Slopes
Choose heavier mulches like wood chips or shredded bark that are less likely to be washed away. Apply mulch evenly at around 10cm thick, starting from the top of the slope and working downwards to ensure it remains in place and provides maximum benefit.
Dig a trench at the bottom of the slope to help hold the mulch in place, especially if there’s a turfed area or walkway at the bottom of the slope where you don’t want mulch to fall onto.
For steep slopes, mulch can be a fool’s errand and you’re better off using geotextiles.
Use of Geotextiles
Geotextiles provide immediate protection against erosion while allowing plants to establish. Secure the fabric with landscape staples and ensure it conforms to the slope’s contours for maximum effectiveness. It’s best to use biodegradable materials that don’t release micro plastics into the environment.
A physical covering on the ground like this allows plants to establish while preventing erosion. https://www.shutterstock.com/image-photo/temporary-covering-lawn-sowing-textiles-ensure-2448627907
Planting Ground Covers
Ground covers can be the most effective solution for controlling erosion beneath hedges and screening on a steep slope. They provide similar benefits to mulch, in that they physically protect the soil, but they have the added benefit of physically holding the soil together with their roots.
Ground-covering plants, particularly strappy-leafed monocots, are fantastic at holding the upper levels of topsoil together, and woody shrubs and trees often have deeper roots that complement the erosion control work performed by those strappy ground covers.
At Ozbreed, we’ve extensively tested a number of strappy plants for erosion control and you can learn more about our findings here: https://www.ozbreed.com.au/best-plants-for-erosion-control/
Choosing the Right Plants
The best form of erosion control on slopes is generally ground-covering plants, which protect the surface from raindrops and also physically hold the soil together with their roots. Selecting the right ground-covering plants is crucial for improving slopes and ensuring long-term stability.
Criteria for Selection
When choosing plants for slopes, look for those with strong fibrous root structures, capable of anchoring the soil firmly. Opt for plants with a compact or low-growing spreading habit, which cover the soil surface and reduce erosion.
Select low-maintenance plants to ensure sustainability and reduce the effort and budget required for upkeep. Hardy, drought-resistant plants often work well on slopes.
Recommended Plants for Slopes
These are the best erosion-control plants which are short enough to be used as ground cover beneath your hedges and screens on a slope.
Lucia™ Dianella caerulea ‘DC101’ PBR
Lucia™ Dianella features deep green foliage with mulberry flower buds in spring that open to purple flowers sitting high above the foliage, followed by purple berries in summer. It grows well in both coastal and inland climates, although it may discolour during very cold winters. It handles frosts down to -7°C with only minor leaf burn. The plant has multiple rhizome shoots, providing excellent coverage and quick recovery from damage.
Erosion Control:
433.75% compared with bare soil.
Size:
30-40 cm high x 50 cm wide.
Preferences:
Lucia™ Dianella thrives in sandy loam to clay soils but should be avoided in very poor soils. It tolerates drought and frost conditions.
Where it Works:
This plant is suitable for use in Queensland (QLD), New South Wales (NSW), Australian Capital Territory (ACT), Victoria (VIC), Tasmania (TAS), South Australia (SA), and Western Australia (WA).
Learn more: https://www.ozbreed.com.au/plant-ranges/strappy-leaf-plants/lucia-dianella/
Little Jess™ Dianella caerulea ‘DCMP01’ PBR
Little Jess™ Dianella is a dwarf variety with short, compact canes that do not fall over. It is renowned for its low maintenance requirements, needing trimming approximately every eight years. This plant produces masses of purple flowers from September to November and is highly drought tolerant, even more so than other Dianella caerulea varieties, including the Breeze® Dianella.
Erosion Control:
181% compared with bare soil.
Size:
40 cm high x 40 cm wide.
Preferences:
Little Jess™ Dianella suits a wide variety of soils but should be avoided in very poor soils. It performs well in both full sun and moderate to heavy shade. The plant tolerates drought, humidity, and frost conditions.
Where it Works:
This plant is suitable for use in New South Wales (NSW), Australian Capital Territory (ACT), Queensland (QLD), Victoria (VIC), South Australia (SA), Western Australia (WA), and Tasmania (TAS).
Learn more: https://www.ozbreed.com.au/plant-ranges/strappy-leaf-plants/little-jess-dianella/
Little Rev™ Dianella revoluta ‘DR5000’ PBR
Little Rev™ Dianella is a very hardy plant with compact blue-grey foliage and an attractive architectural form, making it perfect for modern landscapes. It features masses of small purple flowers from October to November and requires little to no maintenance once established. It performs well on raised slopes but is not recommended for depressed areas that receive periodic flooding.
Erosion Control:
161% compared with bare soil.
Size:
30-40 cm high x 30-40 cm wide.
Preferences:
Little Rev™ Dianella suits moderate to heavy, free-draining soils, and should be avoided in very poor soils. It thrives in full sun to moderate shade and tolerates both drought and frost conditions.
Where it Works:
This plant is suitable for the Australian Capital Territory (ACT), Victoria (VIC), South Australia (SA), Western Australia (WA), Tasmania (TAS), and New South Wales (NSW) (only with good free-draining soil in Sydney).
Learn more: https://www.ozbreed.com.au/plant-ranges/strappy-leaf-plants/little-rev-dianella/
Shara™ Lomandra fluviatilis ‘ABU7’ PBR
Shara™ Lomandra is a tough, fine-leaf compact plant with blue-grey tones and masses of yellow flowers that sit above the foliage. It displays excellent drought tolerance and is highly effective in mass planting landscapes. The plant is also very Phytophthora tolerant, making it suitable for humid climates and heavier soils. Additionally, it is soft and child-friendly without attracting honeybees, perfect for playgrounds.
Erosion Control:
225% compared with bare soil.
Size:
45-55 cm high x 50 cm wide
Preferences:
Shara™ Lomandra suits a wide variety of soils and can tolerate periodic wet feet but not permanent waterlogging. It performs well in both wet and dry areas, as well as slopes.
Where it Works:
This plant is suitable for Queensland (QLD), New South Wales (NSW), Australian Capital Territory (ACT), Victoria (VIC), Tasmania (TAS), South Australia (SA), and Western Australia (WA).
Learn more: https://www.ozbreed.com.au/plant-ranges/strappy-leaf-plants/shara-lomandra/
Evergreen Baby™ Lomandra labill ‘LM600’ PBR
Evergreen Baby™ is a compact, fine-leaved evergreen lomandra that is particularly tough and versatile. It tolerates both drought and wet feet, making it suitable for various environments. This plant produces an abundance of golden flowers in spring and is male sterile. It is ideal for situations where a smaller but resilient plant is needed, providing the same benefits as the larger Tanika® Lomandra but at half the size.
Erosion Control:
210% compared with bare soil.
Size:
40-45 cm high x 45 cm wide
Preferences:
Evergreen Baby™ thrives in a range of soil types from sandy loam to heavy clay. It is highly adaptable and can handle frost, drought, and (unlike Tanika Lomandra) can tolerate periodic wet feet.
Where it Works:
This plant is suitable for Queensland (QLD – not northern QLD), New South Wales (NSW), Australian Capital Territory (ACT), Victoria (VIC), South Australia (SA), and Western Australia (WA).
Learn more: https://www.ozbreed.com.au/plant-ranges/strappy-leaf-plants/evergreen-baby-lomandra/
Tanika® Lomandra longifolia ‘LM300’ PBR
Tanika® Lomandra has been a reliable performer in landscapes across Australia for over a decade. An evergreen plant with an improved compact, fine-leaf form, it requires low maintenance. It features small yellow flowers from April to October and has soft foliage that is child-friendly. Tanika® Lomandra is particularly noted for its drought tolerance, making it ideal for slopes and dryland areas. However, it is not recommended for low-lying areas in Sydney and north due to the prevalence of phytophthora; alternatives include Shara™ and Evergreen Baby™ Lomandra.
Erosion Control:
250% compared with bare soil.
Size:
50-60 cm high x 65 cm wide
Preferences:
This plant is adaptable to sandy, sandy loam, and clay soils but should be avoided in areas with wet feet. It tolerates frost and drought conditions well.
Where it Works:
Tanika® Lomandra is suitable New South Wales (NSW), Australian Capital Territory (ACT), Victoria (VIC), South Australia (SA), Western Australia (WA), Tasmania (TAS), and Queensland (QLD – only for non-humid regions like Toowoomba with free-draining soil).
Learn more: https://www.ozbreed.com.au/plant-ranges/strappy-leaf-plants/tanika-lomandra/
Preparing the Slope
Effective preparation of the slope is necessary to ensure successful planting and long-term stability.
Increasing Soil Organic Matter
Adding organic matter, such as compost, manure, worm castings, etc. enhances soil structure with carbon, meaning that the soil particles stick together more easily. This can help reduce erosion.
Organic matter can be tilled into the soil for a more immediate effect, or it can be laid on top of the soil and the soil biology will eventually incorporate it into the soil. Remember that the organic matter is likely to fall down steep slopes more quickly than it’s able to be incorporated into the soil by the biology.
Organic matter must be regularly replaced as it tends to break down quite quickly, especially in warmer climates. For gentle slopes, mulch can help preserve the existing soil carbon and gradually replace it. Because steep slopes struggle to retain mulch, other methods are more effective.
Good ground-covering plants are anchored into the soil with their roots, and are a more effective way to protect soil on steep slopes. As their roots naturally release organic compounds into the soil, and their spent leaves and roots break down, these ground-covering plants add organic matter to the soil, while their roots physically hold the soil together as well.
Terracing and Contouring
Creating terraces on steep slopes provides flat planting areas, slowing down water runoff and reducing soil erosion. Installing retaining walls made of stone, timber, or other materials helps hold soil in place and offers additional support. Using contour planting, where plants are positioned along the natural contours of the slope, can slow water flow and encourage water infiltration, further reducing erosion.
This can be an expensive project up-front, but is an effective way to prevent erosion long-term and you can save money in the long run on replacing failed plants.
Planting Techniques
Adopting the right planting techniques ensures that plants establish well and contribute to slope stability.
Planting Methodology
Ensure planting holes are wide and deep enough to accommodate root systems without crowding. Proper planting allows roots to spread out and anchor the soil effectively. Space plants appropriately to allow for mature growth and effective ground coverage, preventing competition for resources and promoting healthy growth. Layer different plant types, combining ground covers, shrubs, and hedges, to create a tiered effect that enhances slope stability.
Initial Care
Water management is crucial; implementing drip irrigation can provide consistent moisture without causing erosion. Apply a thick layer of mulch to retain moisture, regulate soil temperature, and reduce erosion. Early pruning practices encourage bushy growth and strong root development, helping plants establish a robust and stable structure.
Long-term Maintenance and Monitoring
Regular maintenance and monitoring are essential for sustaining slope stability.
Regular Inspection
Regularly inspect the slope for signs of soil displacement, exposed roots, and sediment build-up at the slope’s base. Early detection of erosion signs allows for timely intervention. Monitor plant health regularly to ensure plants are not stressed, diseased, or showing inadequate growth, which could compromise slope stability.
Replenishing Mulch and Soil
Reapply mulch annually or as needed to maintain an even layer and continue protecting the soil. Regular replenishment ensures ongoing erosion control.
Pruning and Thinning
Regular pruning helps maintain the desired shape and size of hedges and screens, enhancing their effectiveness in stabilising slopes. Thin crowded plants to improve air circulation, reduce disease risk, and encourage healthy, vigorous growth.
Conclusion
Proper planning and plant selection are crucial for managing slopes. Implementing effective soil and erosion control techniques, combined with long-term maintenance, ensures a sustainable and attractive landscape. By following these strategies, you can enjoy a stable and beautiful garden with enhanced plant health, reduced erosion, and a visually pleasing landscape.
