Berms are the height of landscape fashion. When well done, they can add interest and relief to an otherwise flat yard. Many gardeners build them for privacy.
Poorly done (the majority, I would say), they resemble burial mounds, or worse yet, the sand mounds constructed for septic systems.Berms are like any other landscape feature: in context and in scale, they fit the landscape like a glove. Everywhere else, they look a little silly.
To get a feel for artistic berming, study a golf course. There are few abrupt bumps or artificial-looking hills. Notice how the land undulates, as if the contours had always been there.
They weren't. When a golf course is built, the land is sculpted with a machine, gently rising in some areas, dipping in others, to make the berms look natural. Gradual changes are the key to blending berms into the existing topography.
For gardeners with sloping properties or gentle hills, berms are a natural land form. Dirt can often be regraded to accent existing slopes, following the curves of the land.
Gardeners with flat land face greater challenges. It's very difficult to make berms look natural when the surrounding land-scape is completely flat.
A landscape architect or landscape designer could be enlisted to help with the grading phase of the project.
If space permits, try to vary the height of the berm. Seldom are hills without some changes in height or width. The sheer symmetry of a berm can give it away by making it look contrived.
Widen the berm in some places. And always keep curves gentle. There's nothing natural-looking about a sharp L-shaped bed that mimics the corners of a suburban lot.
Round off the crest of a berm to avoid sharp points or peaks. Gradually feather the soil into the existing grade. It should be hard to tell at which point a berm begins and the original grade ends.
Use landscaping to further blur the line. A lawn that exactly follows the toe of the slope (the point at the bottom of a berm that meets the original soil) is a dead giveaway. Allow the lawn to cross the line in natural "mowable" curves.
If space is tight, consider building a retaining wall to hold the soil on one side of the berm. It's a clever trick, and will, of course, add to the cost of an earth-moving project. But if carefully integrated into the landscape, the wall itself can become a valuable design feature.
Berms can be anywhere from several inches to several feet in height. The size of the property and the purpose of the berm will help establish the appropriate scale.
In small gardens, keep berms generally to 18 inches high or less. Build the berm entirely of topsoil - 18 inches isn't all that deep - and amend the surface for planting.
Higher berms often contain a core of fill dirt or rubble, covered with 18 inches of good soil. Expect some settling as the topsoil compacts and fills the cracks between the chunks of rubble.
Steep berms should be immediately planted with ground covers and spread with mulch to protect your investment.