It sounds like a fairy-tale: Weave a living retaining wall that just gets stronger and stronger as the years pass and continue a tradition that is thousands of years old! Willow Spiling is a natural, sustainable, long-term solution to erosion. A perfect example of rediscovering an old practice for modern times.
This land bridge (huge culvert at the bottom of the ravine) was twice this width when we bought the property in 2014. We have debated and gotten multiple repair estimates and had pretty much resigned ourselves to losing this access point because all estimates were cost-prohibitive. I did find some useful ideas like this planter that I could DIY, but this erosion is past the point of even that helping. Willow Spiling is our last option, honestly our only hope at this point. In simplest terms, Willow Spiling is like weaving a basket along any area with erosion…..but every twig used in the basket is still alive with a root firmly anchored in the soil that continues to grow and get stronger over time instead of rotting and getting weaker.
Willow Spiling is simple and low cost, so for me, a great way to protect from erosion. The traditional technique weaves willow branches into a fence or wall and is currently one of the most popular methods for controlling erosion on slopes in China. We are going to take some time here and explore the history of using willow to control erosion, what specific types are best suited to various conditions, and how you can build them yourself.
The ancient Egyptians used willow as a natural remedy to stop bleeding, treat inflammation of the stomach and for urinary tract infections. But Willow also served the Egyptians by becoming the natural barriers they needed to fight erosion. In England you are likely to come across Wattle fences at historical sites which use dead wood as posts and dead branches as the weaving material into a huge “basket” that protects gardens, play areas or even as the structure for raised garden beds.
It has been used for centuries to provide shelter, create fish habitats and stabilize the soil on riverbanks. The history of willow spiling in the United Kingdom goes back to the late 1600s, when it was used as a river-bank erosion control method. There are currently a few British companies that can come to your property and install this “soft engineering” but that isn’t an option for us, so you can watch over my shoulder as I plan out this project.
The above hybrid of the wattle fence and the willow spiling is sometimes practiced. Here, two parallel rows of trees are closely planted and pruned in the copicing style so that strong trunks form as fence posts. After branch triming each year the branches are stacked between the trunks as a wall of brush. I like the concept, but the thick layer of brush might create unwanted wildlife habitat in your garden or back yard. Perhaps if the rows were placed closer together it might end up tidier.
Willow (Salix) is an Old English word for a plant that has long, slender stems and branches. It was common to see willow trees by riversides because the wood of the tree easily bends under wind or water force. Willow is a tough, versatile tree with over 300 variaties, so I’m only going to touch on a very few.
The Weeping Willow may be the very first image that pops into your mind when ‘Willow’ is mentioned. The weeping variety grows up to 30 feet tall and has long drooping branches that create an arching canopy when in full bloom. The branches have an appearance of hair and grow best in moist soil with plenty of water. This tree is so distinct and iconic that it is good to imagine this version when you consider the process of weaving living branches into a basket/fence/net to catch soil that is eroding away. It’s easy to imagine those long thin branches being used in that that way. If you’ve ever taken care of a weeping willow then you know what it does to the lawn below it too. Not only the grass-killing shade, dodging the branches while trying to mow but also the constant limb/leaf litter. These drawbacks for lawn usage though are assets when trying to grab and rebuild soil that was lost to erosion.
The Pussy Willow is perhaps the second willow that would come to mind with it’s delicate white fluffy pods. The Pussy Willow is hardy for zones 4-8 and propagets as seeds but even more easily as cuttings. A versatile plant that can grow into a 20 foot tall tree or be trimmed into a small shrub that prefers very wet soil. This was my first impulse to purchase for my project, but it prefers full sun and can only tolerate some shade. In mid-summer my land bridge becomes deeply shaded, so I kept looking.
For my erosion problem, I purchased Salix Purpurea L. also known as Purpleosier Willow from Cold Stream Farm out of Minnesota. According to the US Department of Agriculture, this particular strain is best suited for protecting river banks and there is even a male clone ‘Streamco’ available that does not produce suckers to prevent invasive spread. We’ll see. Willows are known to hybridize on their own and add even more confusion to the already crowded 300 species World Wide. In a year I’ll publish an update on the seedling’s health and how well they are doing for this use.
How To Plant and Build
On their own, Willow trees naturally grow along river banks where their roots hold the soil in place during storms and high water flows. Just through nature, this provides stability for your river bank or ravine edge. It grows rapidly and is resistant to strong winds, heavy rain, and even droughts. All this while offering a wide range of benefits, including increased habitat and flood control. They can grow up to 6 feet in their first year, so periodic maintenance is very important (and encouraging) often in the first year. The plantings can be installed on slopes with any degree of incline and have even prevented landslides in some cases. The best time to plant is in late winter or early spring.
We take the natural benefits of the volunteer Willow a step further by ‘weaving’ the saplings into a living retaining wall while they are young and flexible. The best way to install willow spiling for long-term use is by burying it in the ground at least 2 inches below the surface. There are several techniques, one involves planting larger cuttings/seedlings of willow trees straight up from the ground and then weaving between these posts thin long saplings that have been planted at a tight angle (45 degree angle or even tighter).
Another technique is to use seedlings all of the same size and to plant one row at a 45 degree angle to the left followed by another row at a 45 degree angle pointed right. Weave both seedlings going both directions to each hold equal weight…no reliance on a ‘pole’ in the center. The basket above is offered as an example of how that would be constructed.
My ditch is so steep and the erosion is so aggressive, that I plan to experiment with a technique I haven’t heard anywhere. I plan to follow the first technique with an additional step to anchor the retaining wall. After planting the upright row in a straight line and another row at 45 degrees, I’ll then plant smaller willows horizontally straight into the steep ditch walls at staggered intervals. I will then tie these ‘horizontal willows’ to the upright willows with jute twine and begin their process of weaving into the basket fence. I hope over time these anchors will prevent the entire wall tipping over and into the creek.
I first became interested in how I could use my own forest twigs from reading this great book about using green wood to construct projects. The idea of using living saplings was fueled by this book though.
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