Beautiful Berms

Berms do more than screen noises. They make a garden interesting.

Almost a quarter-century ago, the great garden designer Harland Hand was wandering around our new garden in east Denver. We told him we intended to install some rock-garden beds in the backyard. He gazed at us intently and said, “They’d better be really big and really high.” We subsequently put in some very tall—it seemed to us—berm mounds. What we learned was that no matter how high you build it, a berm settles. Gravity prevails.

    “Berm” derives from the French word berme, used to describe a mound built up for fortification. Many Americans are unfamiliar with the word. There are many synonyms—hummock, mound, drumlin, hillock, ridge, knoll, stack, drift, tumulus—but locally, a berm describes the multiplicity of ways we can add relief and drama to the horribly conventionally flat gardens most of us have.

Why do we berm (it can be a verb as well!)? There are many reasons. I have a friend who created a large berm between her home and a busy road because substantial fencing wasn’t allowed, but the ordinance said nothing about building mountains. For plant lovers, berms provide various microclimates for growing plants with different needs. That’s because you control the soil that goes into a berm, and depending on how your berm is oriented to the sun, it can have a shady side for cool-loving plants and a sunny bank for succulents. Plus, a berm’s top is always much drier than its bottom, where you can grow thirstier plants.

And then there’s the matter of drainage. As we learned only too well last fall, Boulder receives the highest rainfall of any Colorado Front Range city. Although drainage is not as great a problem here as in perpetually rainy places, we can experience amazing episodes of torrential rain. Berms are extremely effective at channeling rainfall, and keeping plants out of floodwaters’ way. One classic way to create drainage is to excavate a swale and use the removed soil to make a berm to retain and direct rainwater.

But the most compelling reason for berms is purely aesthetic: They create a third dimension of interest on your property. Most gardens are dreadfully flat. It depresses me to drive through Front Range cities and find for blocks on end the same old lawn, junipers and the occasional edging of annuals or ground covers. We are sadly in need of Harland’s boldness and panache. He wouldn’t hesitate to excavate a deep hole in many gardens to generate soil to berm up into high and ever higher mounds.

Berm Beginnings

My first berm encounter was in the garden of T. Paul and Mary Maslin, on the Hill in Boulder, when I was growing up. Back then, perennials and the unusual tree and shrub were even more rare in gardens than they are today. But on my way to junior high school, just a few blocks away, was a veritable fairyland of exotic and wonderful plants in the Maslins’ yard.

I planned my route to and from school to veer by this amazing garden. Eventually I came to know the owners, and in time they became my very best friends. I was enthralled when Paul would tell me how he constructed his home and garden by himself. He did get help from heavy machinery in the early phases, and hired a front-end roller to contour the property and create a lower-level patch for the house, unearthing hundreds of enormous boulders in the process (the city is aptly named!).

Tractors moved these to the garden’s periphery and Paul bermed the soil into wonderfully sinuous beds. What had once been a very level, rather boring lot now had almost 10 feet of differential from end to end.

In the end, the bermed island beds and banks Paul created around the garden provided several microclimates that allowed him to grow an amazing range of flowers. The overall effect of Paul’s garden, which had a dramatic central pond and waterfall, was very restful.

Paul valued his berms for their horticultural potential and for the way they made the garden so much more complex and interesting. He boasted to me that you could get lost in it—and his garden was not huge—and that you could never see more than a fraction of it from any single viewpoint because the berms blocked some views and framed others.

To this day, the Maslin garden remains the most magical and beautiful garden I ever hope to know—and I’ve visited thousands.

Demo & Drainage

Each and every berm garden is unique. One of the most influential in our region is the xeriscape dem­on­stration garden at Kendrick Lake in Lakewood.

Designed over a decade ago by Greg Foreman, a designer of true genius, this many-acre garden consists of a dozen or so individual flower beds, each of which is mounded with specially mixed topsoil and native subsoil, and amended with gravel and compost. These may be only 2 feet or so higher than the surrounding paths—although the more recent ones are definitely a meter or more to ensure drainage, provide a better soil matrix and, above all, give this flat site mystery and interest.

Greg has told me that the main reason he used berms in the way he did was to provide better drainage, and to allow him to bring in more soil to improve what was there—and lots and lots of sand and gravel to help make that soil even more porous and amen­able to xeric plants. Anyone who has walked through this garden will tell you that it’s almost miraculous how enormous and beautiful every single plant seems to be. They would all win first prize in their category if there were a county fair for xeriscape perennials!

Greg attributes the vigorous growth and the fact that every plant seems to have exceeded its potential to the aeration provided by creating a deeper, more porous soil, and to the gravel mulch that helps keep in moisture and keep down weeds. In 2013, the maintenance crew neglected to turn on the water until most of the summer was underway, and though the garden was virtually unwatered, Greg told me it looked better than ever. Deep roots and careful planning are the garden secrets we should all learn and emulate.

Mount Snyder

Sandy and Bill Snyder were faced with a dilemma: The road alongside their house kept getting busier and the street noise filtered into their house. They decided to build a high fence to screen the noise. City ordinances prohibited anything solid enough that would make a difference, so they could only have a low see-through fence at best. But the city had not proscribed the building of berms.

So build one they did—a veritable mountain of a berm I christened “Mount Snyder,” that must have been 10 feet tall or higher when first installed. The Snyders used large lichened boulders to create an artistic, Western-flavored butte, and planted sun-loving rock-garden plants on the south “Wyoming” side and various heathers and cool-loving plants on the north “Alaska” side.

I was a bit dubious about this mountainous experiment at first, but over the decades I have come to love it more and more as the plants mature and the landscape mellows. The berm easily sank to almost half its original size over the last 20 years. A lesson for berm builders: If you want to keep your berm a certain size, you’ll have to have firm soil at its heart—or perhaps even boulders to provide a sort of “skeleton.”

More importantly, make sure you mound it considerably higher than the height you want it to ultimately attain—I suggest at least a third higher. Truth be told, no one ever builds a berm big enough; we are such timid creatures! But the bigger the berm, the more important it is to have an artistic eye help place, shape and plant it.

Over the years I’ve watched some of the tiny shrubs on Mount Snyder mature. At one point Sandy had what had to be the largest specimen of spiny broom (Genista horrida) outside of Spain. It was nearly 2 meters across before she removed most of it because it was swallowing up too many other gems.

Superb succulents line the sunny side, including a large Chilean cactus (Maihuenia poeppigii) that most people find challenging to grow. This very primitive cactus, which actually has leaves year-round (most cacti dispense with them altogether), blooms prolifically over an ever-expanding mat of verdure. On the north side, various peonies have thrived and self-sown, along with many bulbs and new ground covers, like the rare herbaceous Clematis fremontii.

Berm Bulwarks

As mentioned previously, the word berm comes from a French word signifying a sort of soil barrier around a castle. The Snyders certainly used this element as part of the justification for creating their berm, although the opportunities it provided to grow unusual plants supplanted its original func­tional motive.

There are times and places, however, when berms as bulwarks are essential. I know people who have created large berms to screen not just traffic noise, but also an unattractive neighboring garden or an ugly view.

My neighbor recently created a rather bold berm, which I believe was designed to screen passersby from the view of his dog. As long as the lawn was flat, the dog would run to the edge of the fence and yip incessantly (ask me how I know this) at any creature that walked by—no matter how far off.

Now a sizable berm completely masks the road and the view from the rather simpleminded dog, and the yipping has virtually ceased. Somehow, it’s not as fun to bark when constrained between a fence and a berm.

I loved berms even before they quieted my neighborhood, but now I must paraphrase Robert Frost and say that “good berms make good neighbors.”

 Panayoti Kelaidis is senior curator and director of outreach at Denver Botanic Gardens.