If you are new to landscaping, chances are you’ve seen many “berms” in your lifetime without even realizing that these structures had a name. That’s because, for all of their variations, the concept behind berms is so simple that it's easy to take them for granted. Let’s look at what they are, how to build them, and the reasons why you might want to incorporate one into your landscaping.
What Is a Berm?
A berm is simply a rounded mound of soil (and, sometimes, fill) built up on an otherwise level patch of land to improve the design of a property. The fact that a berm is rounded is what distinguishes it from a raised bed. The latter has a flat surface and a rectangular shape.
Supplies to Build a Berm
- Flexible garden hose
- Spade, shovel
- Steel rake
- Tamping tool
- Fill, such as rubble or gravel (optional)
- Clayey soil (optional)
- Edging material (optional)
- Boulders (optional)
Basic Berm-Building Rules
There are few hard-and-fast rules in building berms, but beginners should use the following guidelines:
- Make the slope gradual. Not only will this look more natural, but it will also help you prevent erosion. Don’t try for a height much greater than 2 feet, and expand the base about 5 feet out in width for every 1 foot the berm rises up. The 5:1 ratio is just an average, though, because you should vary the slope to create greater interest. Give the berm more than one peak, and avoid putting the highest peak in the center of the berm.
- Berms are more interesting if they are shaped like kidney beans or crescent moons than if they are circular.
- Be mindful of potential drainage issues at all times while planning and building your berm. Remember that erecting such a structure in your yard can have the effect of channeling rainwater towards areas of the land where it was never intended to go. This is why it is better for a beginner to build a berm that is of relatively small size and to stick to building just one berm. In the worst cases, you may have to install a drainage system.
- Dirt piled up willy-nilly may well erode away when it rains unless you pay attention to how you layer your berm, assuming that you want to avoid the cost of a berm composed totally of topsoil (loam). To save money, use topsoil as a top layer (it is great to grow your plants in), but use clayey soil as a second layer, not a fill such as gravel or rubble. Clay is a type of soil more impervious to water than is fill, so your topsoil won’t percolate through it. Underneath the clay, use fill to build up the bulk of the base.
Step-by-Step Instructions to Build a Berm
In the planning stages, first be sure to call "Dig Safe" Phone Number (or its equivalent in your area) so that the presence of underground utility lines, etc. on your property can be marked. The location you choose for the berm will depend on the function it will serve for you. If it will serve as a planting bed for a flower border intended to be seen from the street, choose a location close to the street. Regardless of the exact location, let’s assume that you will be building the berm in what is presently a lawn area. Here’s how to proceed:
- Using a flexible garden hose, mark the berm’s border. Step back and evaluate the design you just laid out. Adjust as necessary. Once you are satisfied, pour flour along the course marked by the hose and remove the hose. You now have the outline for your berm.
- Following the guideline furnished by the flour, plunge a spade into the ground all along this outline.
- Working inside the outline, remove all of the sod using the spade.
- Also, remove any topsoil left over in the area after digging out the sod.
- With a wheelbarrow, dump the fill to begin building the base. Take a lot of time to get the shape and slope right, because the next two layers will follow the shape of this layer (so this is the time to make adjustments, not when you’re applying the clay and the topsoil).
- Keep the fill a foot or so away from the border (you’ll want to place topsoil here). In fact, minimize the depth of the fill where it’s closest to the edge, but gradually increase its depth as you work toward the middle.
- Apply the layer of clayey soil. Rake it out evenly. Tamp it down.
- Apply the layer of topsoil. Rake it out evenly. Tamp it down. Spray it with water to remove air pockets. How thick this layer needs to be varies depending on plant size, but more is better. Even some small plants need at least 6 to 12 inches of good soil to root in.
- Install plants in the berm, using the same landscape design principles you would use anywhere in your landscaping, and apply mulch.
Berm Building Tips
Edging material and boulders are optional supplies here. Here's how they can be useful:
- Because erosion is such a concern in this project, ringing the berm with edging gives you something of an insurance policy: the edging will trap any soil that washes down the slope. Stone makes for a simple edging.
- Boulders embedded in a berm (iceberg style, with a portion sticking out of the top, but most of the boulder down under) not only add to the aesthetics of the design but also take up space, meaning there's less filler to worry about.
Reasons to Build a Berm
At the most basic level, incorporating a berm in an otherwise flat yard is about raising the viewer’s eye level. Flat expanses are boring, and injecting a vertical element makes such a space more interesting. But, in addition to this most fundamental of reasons for building one, consider that a berm can benefit a landscape by, for example: