Building Berms: Lessons Learned by Nancy Shepard

2022 front yard with berm, four years after installation. Photo by Nancy Shepard

When we replaced our front yard landscape in 2018, I wanted to make our yard a little more private. We live on a corner and even though the traffic is minimal, it made sense to not only create a bit of privacy, but also give the yard a bit of visual dynamic. 

We had ripped out many old juniper bushes around the perimeter of the corner and now had bare ground. The soil under the junipers was a combination of rock and gravel, not exactly what you want for planting new trees and plants. 

After juniper removal, Photo by Nancy Shepard

So we decided to mound that wretched “soil” to create the base for the berms on which we would put better soil. We first tried to remove as much of the rock and gravel as we could by building a sifter box that sifted the dirt away from the rock and gravel.

Sifting gravel out of berm soil. Photo by Nancy Shepard

Researching berms I read how to make the slope gradual. Not only will this look more natural, but it will also help to prevent erosion. Don’t try for a height much greater than two feet and expand the base about five feet out in width for every one foot the berm rises up. This 5:1 ratio is just an average, though, because you could vary the slope to create greater interest. Most berms in home gardens are no taller than 24 inches.

Building the berm base with gravel and dirt. Photo by Nancy Shepard

I read that you are supposed to build the base from affordable materials. (We had plenty of that!)  We piled up the sifted dirt even though it still had gravel in it and compacted it. We shaped it according to the layout we wanted, except one foot smaller on all sides. Then we raked it smooth to get all proportions as exact as possible. I read that you're supposed to put a layer of clay soil over the base before putting down your topsoil. This is the part I unfortunately ignored. Yes, the still gravely dirt was cheaper, but the topsoil tends to wash through it. Clay is a type of soil more impervious to water than is fill, so your topsoil won’t percolate through it. We continued by adding top soil (dirt amended with compost.)

Top layer of berm covered with good soil. 

Mistake: using landscape fabric. Photo by Nancy Shepard

We topped the berm areas with finely shredded "gorilla" type bark. After tamping it down, this proved to stay put in the winds and conserve water. I made the mistake of using landscape fabric in the non-berm areas. This was before I was trained as a Master Gardener and I thought this was best practice (it isn't.) As a result, when we plant in the non-berm areas, we have to remove quite a bit of the fabric to help the soil breath. Someday I hope to remove it all except for the places that have rock on it.

We also added moss rock that we embedded into the sides of the berm so they look like partially covered larger rocks. This had a nice effect to look like it was more aged.

 

Embedded moss rock. Photo by Nancy Shepard

Now, four years later, the berm is a challenge for some plants because of the still-gravely soil. But I side dress all the plants with compost and good soil each year to replace any top soil that may move down because of the gravel. Interestingly the trees seem to like a bit of gravely dirt.