Soil erosion prevention on slopes and hillsides can be overwhelming for most property owners, especially in California. Not only do they present potential risks to your property and household, but they also can require extensive time and investment to address.
Engineered terracing and retaining walls are the most reliable means of stabilization, but in most cases, fortunately, another option exists: installing native plants.
Research shows that sloped gardens with a variety of native plants can effectively mitigate erosion when they are properly planned and installed. Unless the slope is exceptionally steep, where engineering is the only option, native plants are a sustainable and approachable means of soil erosion prevention.
Before you begin your planning and planting process for soil erosion prevention, the Besanti Natives California native plant experts recommend you consider the following factors:
Examine Current Soil Erosion Prevention Measures
When you’re trying to prevent erosion on a hillside, you have to consider what’s working and what is not with the current situation. If you were to step on any given part, would you be stable, or would the ground crumble beneath you?
Knowing the intensity of your current erosion and having a sense of its relative stability will help you decide what type of professionals your soil erosion prevention project needs.
Understand the Steepness of the Slope
The steepness of your slope will have a major effect on how you approach the stabilization project. What is the degree of the incline? Is it easy to walk up, or do you need to crawl/climb up?
It's also important to know the steepness because it will affect how you can approach the labor of your project. If the slope is too steep to scale up by foot, are there any paths or stairs in place? If not, would it be feasible to install them in the future?
Additionally, it's important to know whether it would it be possible to push a wheelbarrow and other tools up and down the hill, or if you will need extra help for manually carrying everything around.
Beyond the short-term planning for the project work, you also have to plan for how you will maintain the finished hillside garden. When you’re establishing your new plants, how will you be able to prune and water them?
While it's possible to choose plants that do not need much supplemental irrigation or pruning, it may not create an attractive end result. If you or a landscaper cannot easily reach the farthest parts of the hill to maintain plants, we recommend calling in an engineering professional before proceeding further.
Get Familiar with Your Soil Composition
Your soil type is one of the most important factors in choosing the right native plants for your soil erosion prevention. Different soil types not only affect the growth of the plants, but they also can have different erosion patterns.
To assess the composition, dig a foot down into the soil. It's important to dig this deeply because the top of the soil may have been eroded and amended over time and will not reflect the conditions in which your plant roots will be growing.
Pick up a handful of the soil and feel the texture. Is it gritty and dry? Soft and damp? Slippery and stiff? Soil can be sandy, loam, or clay, but usually it is a mixture of at least two of these. In the Los Angeles area, for example, the soil is almost always sandy or loamy sand.
Knowing the soil type will impact your plant selection as well as your overall approach to stabilizing the area. Sandy soils are prone to drying out more quickly and eroding from wind, like a sand dune. Meanwhile, clay soils are prone to muddiness and sliding erosion during storms.
Test the Speed of Your Soil Drainage
As it would be with any gardening project, it’s important to see how quickly your soil drains on the slope. Most native plants in California need well-draining soil to avoid rotting roots, but there are plants that have adapted to slow and stagnant draining soils as well.
To conduct a soil drainage test, dig a hole that is one foot wide, one foot long, and one foot deep. Fill it to the top with water and note the time (or set a timer). If the hole drains within an hour or less, it is fast-draining. If it drains within the next 12-24 hours, it is medium draining. If it takes 24+ hours, it is slow draining.
As with the composition analysis, digging this deep is important, because it helps you assess the soil where plants will be growing roots. Testing only the top few inches of soil may distort your test results. If your soil has compacted over time, water may be very slow to drain through the top layer, but will drain easily through the ground below.
Look for Rocks Under the Soil
Rocky and serpentine soils can require specific types of plants that are able to grow roots among the rocks. Sometimes this is apparent, when the ground has permanent bald spots without plants and soil, or large boulders are visibly jutting from the ground.
If you’re unsure about the rockiness of your soil, dig a hole in a random spot (not where you are planning to plant anything, just yet). Check whether there is solid rock or smaller stones under the top inch of soil. If you've conducted the composition and drainage tests above, you will also have an idea of the rockiness.
If you encounter significant amounts of rock in your slope, do not be discouraged. There are numerous remarkable California native plants that have adapted to live in these exact conditions.
Find Any Mud that Inhibits Soil Erosion Prevention
Soil erosion prevention starts with stabilizing the earth, especially if there is mud present. Check out the soil when weather conditions are dry and it has not rained in the last 48-72 hours.
If you encounter mud or soil that is very soft under your feet on the slope, you are at an especially high risk of significant erosion. These areas in particular will need trees, as they have the deepest and most sprawling roots to stabilize the ground. You will also likely need to create an additional means of channeling water runoff, like a dry river bed, to reduce the sogginess of the soil.
Explore Water Runoff Patterns
Controlling water runoff is one of the most vital aspects of stabilizing a hill and soil erosion prevention. Allowing water runoff is a fast track to erosion.
There are a few ways to determine if you have water runoff issues. First, consider what you see when it rains. How fast does the water move? Where does it go? Does it penetrate the ground, or does it flow freely down the slope?
If you have seen this free flow of water, what is the pattern of the runoff? Does it go straight down, or does it move side to side? Does it flow across the entire hill, or does it flow inside of channels?
Additionally, you may be able to notice signs of water runoff even when the slope is dry. Usually if there is a runoff problem, there will be visible channels and fissures in the dry soil where water has eroded the hillside.
Document Your Hill's Sun Exposure
The evaporative effect of the sun can play a key role in the stability of your slope, as well as influence your plant selection. To start, what direction does the hill face? In the northern hemisphere, southern and western slopes typically receive the most intense sunlight throughout the day.
Also consider the amount of time that the sun shines on the area. Is the slope full sun, part sun, or shade? Does this change during certain parts of the year? If you have large trees that shade the slope, is most of the sunlight obscured on the hill, or do shadows fall elsewhere?
Finally, is the strongest exposure in the morning, midday, or afternoon? Areas with hot midday and afternoon sun may dry out your soil and plants more quickly and lead to crumbling erosion. whereas shady hillsides could have more areas of moisture that can suddenly sink during heavy rains.
Test Your Mineral Composition
The mineral composition of your soil typically will not be extreme enough to require special testing, but there are some cases when it is very helpful. If you’ve had difficulty growing plants in unamended soil elsewhere on your property in the past, we recommend you conduct a mineral composition test to check the sodium, boron, and calcium levels in your soil.
You can buy a test kit online or from a specialty shop, depending on the level of analysis you think is appropriate. In your results report, you may see a section advising you on recommended amendments. Save yourself the unnecessary work of amending the soil and ignore those instructions.
It may sound counter-intuitive, but amending the soil is not a sustainable approach to planting on your hillside for soil erosion prevention. Amendments have to be added year after year, which is laborious and time-consuming. It can even lead to unintended consequences for local wildlife because your soil can suddenly become out of balance with its surrounding ecosystem.
Use your new-found knowledge to work with the soil, rather than fight it. For example, if you live within 10 miles of the coast, you may have salinated soil. Fortunately, many beautiful native plants have adapted to California’s coastal environments and will grow freely in this unique soil without issue.
Review Your Current Irrigation System
Do you have an existing irrigation system or water access point on the hillside? Ideally, you will have some irrigation available here, especially for the first year that you are helping your plants establish their deep roots.
While it’s possible to grow new plants on the slope without water, your plants may not look as attractive as they could be. Moreover, an unirrigated area will be more vulnerable to wildfires, especially if they get full sun exposure.
Fortunately, irrigation systems do not have to be particularly extensive. Keep the system simple and tailored to your native plant selections, as adding too much water at a time will further destabilize the slope.
Identify Existing Plants in Soil Erosion Prevention
Using a variety of plant species and forms will be critical to stabilizing your slope. Oftentimes, slopes are bare or have only a single type of plant. This makes them especially vulnerable to dangerous erosion.
Imagine that the plants on your hillside form a type of net that secures the soil. If you have a thin net that is loosely secured, it can keep some of the topsoil from falling down, but it won't be much of a help if the lower layers of soil become loose and start to erode.
If all of the plants are the same type, such as a slope filled with invasive English Ivy, their roots form a flimsy net into only a single layer of soil. While this net may prevent minor erosion of topsoil, significant rain and wind can destabilize the layers below it. As such, the underlying soil could suddenly give way, and with only that one flimsy net, nothing would be able to stop it.
In contrast, consider what would happen in this situation if you had multiple sturdier, more tightly woven nets that were integrated into the hill at range of depths with stronger ties. Here, you could prevent soil erosion more easily, because you now have many layers of the ground secured.
This strong, sturdy net is created when you plant a mix of native trees, shrubs, perennials, and groundcover into your hillside. The strong roots of native plants will reach a range of depths, stabilizing the earth below. When weather is extreme, there may still be some natural shifts in the soil; however, this erosion would be more shallow and isolated to single, small areas, rather than the entire hillside.
Prepare to Start Your Soil Erosion Prevention Project
Ultimately, once you have considered all of these factors, you'll be ready to start choosing your plants and their placement for optimal soil erosion prevention. If you're still looking for advice on soil erosion prevention, contact our certified California native plant experts today to help you create a beautiful, and more secure, hillside garden.
About Us
Besanti Natives is a landscape design consulting firm in Los Angeles specializing in bespoke outdoor spaces inspired by the natural wonders of the Golden State. Our Certified California Native Plant Landscapers offer a refreshing, holistic approach to your landscape to help you cultivate more meaningful connections to nature, your loved ones, and yourself.
Our team is dedicated to preserving the unique character of each property while providing modern solutions to enhance functionality and beauty. To order any of the plants listed on this page, learn more about our services, or to schedule a consultation, visit our online booking page.
