Yo, it’s your hip, non-hipster gardener here to discuss another crazy crime against horticulture: the badly planted berm. We have ALL seen it. You are driving along and someone has tried to recreate the Blue Ridge Mountains along their property line. People want to create a natural screen, while deadening the sound coming from say the neighbor’s garbage, I mean garage band or amateur drag racing strip. I would too, if I were in their shoes. They go through all this work to sculpture their mountain ridge and then come to me and say, “All my lovely pine trees are dying! Oh what is happening?!” The soil has washed away, exposing the roots of the trees they chose to plant on the very top ridge. Question: how many plants have you seen growing naturally on the top of a sharp peak? Why is that? It is called hot and dry, folks. There is little room for roots to spread out, as they are want to do, so there are few roots available to absorb moisture. Of course the peak also is the first part to dry out in any contoured situation at any scale. So, we need to do a little designing and considering before we take all that excess subsoil filled with brick your neighbor is offering to you with a wink and a big toothy grin.
First, take time to do a little designing; ask what is the purpose of this berm you are trying to create. Berms can serve more functions than just sound reduction and privacy screening. They can add elevational interest to a flat mid-western yard. They can redirect traffic flow or water flow (need this one in my backyard), or get roots out of wet or contaminated soil. Regardless of the purpose, THE BERM SHOULD LOOK NATURAL AND FIT INTO THE LANDSCAPE. At a minimum, it should be well framed with something that ties it naturally into the existing grade and context. A retaining wall, a fence backing the berm, anything that gives a nice transition from one grade to another. The worst offenders I have seen are the abrupt rises of piled soil like someone just dumped some soil and raked it out (which is what they did) prior to sticking some poorly thought out plant choices.
Regardless of what your design purpose might be the most critical to get right is the berms dimensions, especially in terms of width and height in cross-section. This will determine aesthetic as well as biological success. The plants have a chance of surviving to do what you want them to do.
You can see in the first photograph an example of as poorly constructed berm. Notice the amount of dead material from previous seasons. Note the alive things on the berm called weeds. This berm is almost as tall as it is wide. Not a good ratio for berming. The second photograph depicts a “successful” berm design. Notice how broad the berm is compared to its height. This berm allows for an ornamental tree to grow along the top of the berm because the “ridge” is wide enough to accommodate roots. Taking time to design properly will allow you to live with your yard on good berms.
Horticulture and Facilities Manager