Building A Berm: How Do I Make A Berm

Building A Berm: How Do I Make A Berm

By: Nikki Tilley, Author of The Bulb-o-licious Garden

Berms are an easy way to add interest to the landscape, especially those with dull, flat areas. Building a berm isn’t as complicated as one might think. By following a few simple guidelines in the design of your berm, landscape troubles can easily be eliminated. If you are wondering “How do I make a berm?” Read on for the answer.

Berm Design

Before building a berm, a landscape designer or yourself must first plan the berm design. Always consider the berm’s overall purpose beforehand as well as drainage patterns within the landscape. On average, a berm should be about four to five times as long as it is high, gradually trailing out into the remaining landscape.

Most berms are no higher than 18-24 inches (46-61 cm.). The berm design can be created with more than one peak for additional interest as well and shaped to perform its purpose. Many berms are given a crescent-looking or curved shape, which is more natural looking and preferable.

Building a Berm

Berms are oftentimes constructed using some kind of fill such as sand, plant debris, rubble or asphalt and soil. Simply use the fill material for the bulk of the berm, forming its shape around it with soil and firmly tamping.

To create the berm, outline its shape and dig any grass. Add the desired fill to the excavated area and begin packing around it with soil. Continue piling on the soil, tamping as you go, until reaching the desired height, carefully sloping it outward. The peak should be situated toward one end, rather than the center, for a more natural-looking appearance.

It may also help to spray water on the berm afterward to fill in any sinkholes that may be present. If desired, plants can be incorporated for additional interest.

Island Bed or Berm

Island beds and berms are very similar. In fact, some consider them much the same. Generally, an island bed floats alone in the landscape, whereas a berm essentially becomes a natural part of the landscape. Island beds are typically created for aesthetic reasons, while berms tend to serve a more functional purpose, such as redirecting drainage or adding raised elements.

Island beds can take on nearly any shape, from round to square. Berms tend to be curved. Size is also variable with island beds, but since these are viewed from all directions, they are usually half as wide as the distance from where they are viewed.

There are no special rules for building a berm. Landscape contours will determine much of the berm’s design, as the remainder lies with the property owner’s individual preferences and needs. The answer to “How do I make a berm” is as simple as that.

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How to: Building beautiful berms

If your customers have a fairly flat landscape and desire a little height variation throughout, why not give berms a try?

Berms are mounded hills of dirt constructed for blocking out unwanted or unsightly views, creating a subtle sense of privacy, directing or redirecting drainage and foot traffic, emphasizing a particular focal point or adding raised elements to the garden.

Not to be confused with the infamous mulch volcano, which are eight to 12-inch piles of mulch stacked around the trunk of a tree, berms are mounds of soil that can sometimes have a small layer of mulch spread over the top. They may look very similar at a first glance, but the two are very different.

If your customers like the idea of having a bit of height in their yard and want to experiment with a berm, check out a few tips to keep in mind that will help you build a better berm and explain its benefits.

Making the berm

Creating a berm isn’t too complicated. Once you begin constructing it, you will typically use some sort of fill material like plant debris, sand, soil or rubble, and this material can be used to make the bulk of it. As long as the material can stably retain without deteriorating, it can be used as the fill material. To ensure more vigorous plant growth, it is recommended that you incorporate compost into the soil.

Before ever starting on the berm, be sure you talk with your customer and have a plan in action. Also, be sure to talk to him/her about drainage options within the area that surrounds the berm, as it could redirect runoff to other areas, affect drainage patterns or encourage pooling after it rains.

Generally speaking, berms should be about four or five times as long as they are high, and they will gradually trail off out into the lawn. There are many ways to create berms, and each one can vary in size and can have more than one peak. Berms can be as deep as your customer desires, but typically, they are no taller than 18-24 inches.

Berms can be made into pretty much any shape, which makes them handy for landscapes that might not have the most traditional measurements, but for a more natural look, stick with the curving shape. They can run the expanse of the yard in a flowing fashion, or they can be edged with stone and plants to give them a more formal look. Adding a border to a berm can also help cut down on the soil eroding into the lawn.

When starting the process, begin by outlining the shape of the berm with chalk, spray paint or flour. Remove the sod and load the bottom of the berm with whatever fill you’ve chosen and pack down around it with soil. Continue to pile the soil to create a sloping mound, and keep in mind that when you’re shaping the berm, pile the dirt into a shape that will mimic the landscape around it.

The goal of a berm is to blend naturally with its surroundings and enhance the overall design that’s already present. Take time to step back when building and shaping the berm to see how it’s progressing and blending with the area around it. If you see that it’s sticking out more than blending, try taking it in a new direction.

Always remember that the transition between landscape and berm should be smooth and gradual, and contrary to popular belief, its peak should not be located in the middle. To help keep a more natural look and help balance out the berm, the peak should be located more to one side. There can also be more than one peak per berm, but these peaks should vary in their height, width and sloping.

Once the berm is complete, tamp it to prevent possible collapsing. Tamping will also help keep air pockets from pushing up plants and ultimately drying them out. It also helps to water a brand new berm and follow that by tamping it again to make sure it doesn’t develop sinkholes. If this does happen, be sure to add more soil and continue tamping until it feels solid.

Planting options

Once the berm’s complete, it’s time to choose what all your customer wants in it.

When picking out plants, keep in mind that there will be microclimates within the berm that will affect whatever plants you select, and also keep in mind that water will drain faster at the top of the berm, so choose plants that can tolerate drier conditions for that section. To contrast that, plants that love moisture would enjoy being at the bottom of the berm.

Because of the berm’s slope, remember to keep an eye on temperatures throughout the year. Plants facing the east and north will be cooler, and plants facing the west and south will be warmer.

Having plants in the berm will also emphasize its shape, so talk to your customer about having a multitude of plant forms, heights, textures and heights present, as this will help the berm’s look and appeal last year-round.

Shorter plants should be located at the top and down the sides of the berm, and taller varieties will look better in the back, depending on the overall shape of the berm.

As mentioned earlier, berms will have a layer of mulch on the top of the soil, but they won’t be completely made of mulch. Keeping that in mind, finish off the berm with a healthy layer of mulch to help keep soil erosion at bay, provide insulation and slow down water.

Shredded wood is usually a good option for berms since it’s less likely to wash down in rain, and it also will blend in well with the surrounding landscape.

Share All sharing options for: How to Build a Rain Garden to Filter Run-Off


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During a downpour at a typical house in many municipalities, water gushes out of downspouts, across lawns treated with pesticides and fertilizers, into an oily street, and, finally, down a storm drain that dumps that pollution along with the water into a stream, river, or bay.

By building a rain garden, you can divert your gutter water into an attractive planting bed that works like a sponge and natural filter to clean the water and let it percolate slowly into the surrounding soil. Installing a rain garden isn't difficult if you're willing to dig or you bring in machines to help.

Ask your local Cooperative Extension Office for specifics about soil mix, garden size, and plants for your area. Then you're ready to build.

Step 1: How to Create a Rain Garden

Illustration by Washington State University Rain Garden Handbook for Western Washington Homeowners

The plants and amended soil in a rain garden work together to filter runoff. Generally, a rain garden is comprised of three zones that correspond to the tolerance plants have to standing water the better a plant can handle "wet feet," the closer it is placed to the center of the garden.

Whenever possible, shop for native and drought-tolerant plants, keeping in mind that parts of a rain garden remain wet for long periods of time, while others are drier. Zone 1, the centermost ring of the rain garden, should be stocked with plants that like standing water for long periods of time, such as Lady fern (Athyrium filix-femina).

The middle ring, Zone 2, should have plants that can tolerate occasional standing water, like Snowberries (Symphoricarpos albus). The outermost ring, Zone 3, is rarely wet for any length of time and is best planted with species that prefer drier climates, such as western bleeding heart (Dicentra formosa).

For more information on building a rain garden, visit the Washington State University's Extension website.

Step 2: Find A Site That Can Absorb Water

Although a low-lying area might seem like a natural for a rain garden, you need a place that isn't overly soggy already. Stay at least 10 feet from the house and at least 50 feet from a septic system or slopes greater than 15 percent.

Call 811 to make sure underground utilities aren't in the way. Once you have a tentative site, test the soil's percolation rate. Dig a hole 2 feet deep and time how long it takes for 8 to 12 inches of water to disappear.

For example, if 8 inches drains in 12 hours, the rate is 8 inches divided by 12 hours, or 0.67 inches per hour. A rate higher than 0.5 is great—your rain garden needs to be just 18 inches deep. If the rate is lower than 0.5 you'll have to dig 30 inches deep.

If the percolation rate is less than 0.1, the site isn't suitable for a rain garden.

Step 3: Determine the Size and Shape

Your local extension office may have information to help you size a rain garden to suit rainfall patterns typical in your area. The ideal size might be smaller than you expect. On well-draining soil in rainy western Washington, where this project took place, a rain garden just one-tenth the size of a roof handles 99 percent of its gutter water.

But if you're short on space or puzzled about how to calculate the size, you can always put in a small rain garden and figure that the good it does will at least be better than what's happening now. If you want an impressive-looking garden, make it at least 150 square feet. Ovals, kidneys, and teardrops often look best, but rain gardens can also be long and skinny. Use a garden hose to test possible shapes.

Once you settle on a design, decide where the water will flow in and where any overflow will exit. Mark the shape with spray paint. On your lawn, mark 18 inches farther out for sod removal, since grass has a way of creeping into planting beds.

Also mark any other areas you want to excavate. The outline of this rain garden juts out at the bottom to show the perimeter of a dry well, an optional underground storage basin for excess water when the rain garden overflows.

Step 4: Remove the Grass

Strip away any lawn by slicing off the roots with a sharp spade directed at as low an angle as you can manage, or use a sod cutter, which you can rent for about $80 a day. You should be able to roll up sections of the stripped lawn as if they were pieces of carpet.

Step 5: Excavate the Basin

Using a shovel or an excavator—you can rent one for about $230 a day or just hire an operator—dig down to the depth you need. Create a flat bottom so that water will percolate down evenly. If the rain garden is on a slope, you can pile some of the excavated soil into a berm on the low side to retain the water.

For stability, stomp the berm soil down well and make the base at least 2 feet wide and the top at least 1 foot wide. The peak of the berm should be at least 6 inches higher than the water level when the rain garden is full.

Also excavate for a dry well, if included the one for this rain garden is about 2 feet square and 3 feet deep.

Step 6: Lay the Inlet Pipe

Dig a trench for a pipe that will carry water from one or more gutter downspouts to the rain garden. (Note: If you can corral helpers, this can be done at the same time you excavate the rain garden.)

Install the piping. Rigid piping with smooth walls is the most durable, but corrugated tubing is easier to work with get the kind without perforations. Extend the piping into the rain garden basin by a foot or so.

Line the area underneath with stones to prevent erosion. You can also place stones over and beside the pipe to hide it and to keep corrugated tubing from curling up.

When all the piping is in place, fill in the rest of the trench with excavated soil.

Step 7: Fill the Basin

Fill all but the top 6 to 12 inches of the excavated area with rain-garden soil. Slope the sides gently. If the soil you excavated is relatively free of clay, you can use a mixture of 65 percent native soil to 35 percent compost, or 2 scoops of soil for each scoop of compost.

If you dug out clay soil, refill with a mixture of 60 percent screened sand and 40 percent compost. If you are creating a dry well, fill that with washed round stones 1½ to 2 inches in diameter.

Also pack stones around the overflow area to prevent erosion.

Step 8: Add Plants

Group plants in zones, based on how well they tolerate having "wet feet" (see Overview). Plants that thrive in the wettest environment go in the center of the rain garden that area tends to stay wet the longest after a storm.

Put plants that can handle standing water on the sloping sides, and those that are suited to drier conditions on the edges.

Step 9: Mulch Around the Plants

Once the plants are in the ground, cover the inside of the rain garden with a 3-inch layer of mulch to keep the soil moist and to prevent weed seeds from sprouting.

Until a rain garden's plants are established, even drought-tolerant plants require supplemental watering to survive dry seasons.

Check the mulch depth annually and replenish as necessary. Rain gardens don't require fertilizers beyond the compost used in the soil mix. Weed and prune to keep the rain garden looking its best.

Step 3: Digging out the garden and adding soil

Helpful Tools: Pick-ax (or digging iron), shovel, garden hoe, and wheelbarrow (or bucket)

Following the established outline for the garden, dig down and remove six to eight inches of the soil with the deepest part of the garden located in the center. If the soil is compact, a pick-ax might be best used to break-up the soil before removing it with shovel and wheelbarrow.

The removed soil can be used to provide the base of the berm, or the elevated side of the rain garden. The berm acts to help direct the water towards the deeper center of the rain garden.

The height of the berm can vary but should be approximately six to eight inches above the ground level or 12-16 inches higher than the lowest point of the rain garden. The berm is a combination of the removed soil from your hole plus extra amended soil on top to provide more nutrition to rain garden plants (see below for recommendations for type of soil to use.)

Photo © Nature Walk School

If the site for your garden is flat, you may choose to build a berm around the entire garden, essentially creating a circular depression. The berm also provides a “dryer” area in your rain garden. If the soil you remove from rain garden is clay-rich, you may need to amend the soil in the berm with sand so that absorption is still maximized in the berm.

Most soil types will require adding new soil to your rain garden to support the native plants you will be adding. The composition of the soil that you add to your rain garden can vary slightly depending on of your existing soil. Ideally the newly added soil is:

Rain Gardens: Read Next

Rain gardens capture water and prevent runoff. But they have a number of other benefits to the permaculture garden where the goal is to use free water for irrigation.

Another way to capture free water is to first capture water in a swale, and then send the overflow into a rain garden. This is what we did in our front yard.

Whether you intend to use the water for your garden or you just want to take responsibility for the runoff on your property, rain gardens make a beautiful addition to a landscape.

What strategies have you used to capture runoff?

Watch the video: Brad Lancaster demo: Learn how to build a Berm with a bunyip water level