By: Teo Spengler
Every tree needs adequate water to thrive, some less, like cacti, some more, like willows. Part of the job of a gardener or homeowner who plants a tree is to provide it with enough water to keep it healthy and happy. One technique that assists you in this task is constructing a berm. What are berms for? Do trees need berms? When to build a tree berm? Read on for answers to all your questions about berms.
A berm is a sort of basin constructed of soil or mulch. It serves to keep water in the right place to drip down to the tree’s roots. Planting trees on berms makes it easier for the trees to get the water they need.
If you are wondering how to make a berm, it isn’t difficult. To build a berm, you construct a circular wall of soil that goes all around the tree trunk. Don’t put it too close to the tree, or only the inside of the root ball will get water. Instead, build the berm at least 12 inches (31 cm.) from the trunk.
How to make a berm wide enough? Use soil or mulch to construct the wall. Make it about 3 or 4 inches (8-10 cm.) high and twice that wide.
Lots of trees grow perfectly well in fields and forests without berms, and most trees in the backyard may not have berms either. Any tree that is easy to irrigate may do just as well without a berm.
Planting trees on berms is a good idea though when the trees are isolated on the far corner of your property or located somewhere that is difficult to irrigate. Trees in remote locations require the same amount of water they would if planted nearby.
Berms are great for trees on flat land you intend to water with a hose. All you have to do is fill up the basin and allow the water to drip slowly down to the tree roots. If you have a tree on a hill, create a berm in a semi-circle on the downhill side of the tree to stop rainwater from flowing away.
In theory, you can build a berm around a tree whenever you think of doing it and have the time. Practically, it’s a lot easier to get it done at the same time you plant the tree.
Building a berm is easy when you are planting a tree. For one thing, you have lots of loose soil to work with. For another, you want to be sure that berm construction doesn’t pile extra soil on top of the root ball. This can make it more difficult for nutrients and water to sink through to the roots.
The berm should start at the outer edge of the root ball. This too is easier to gage at planting time. Also, the period the tree will need extra water starts at the time of planting.
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A flat, featureless lot doesn't need to stay that way. A berm -- a low hill you can construct yourself -- creates interest in a flat yard by changing the grade. Building a berm is a project that doesn't require advanced DIY skills. A solid plan, the correct materials and some muscle power will have your berm built in no time.
Perfectly flat land might make it easy to mow your lawn, but flat land lacks the visual interest of a rolling landscape. Berms -- small, elongated hills with a gradual slope -- add height so you can showcase plants on a raised platform. You can use a berm to create a privacy screen with small trees, to divide sections of your yard or simply to add dimension to your outdoor space. Berms look most natural when they are only 2 to 3 feet tall and should be four to six times as long as they are wide.
Sketch the design of the berm to scale on graph paper before committing to the design so you can make sure you have enough room to build a berm that looks natural in your space. Berms to showcase trees should slope out horizontally 5 to 7 feet for every 1 foot of height berms for small plants can thrive on steeper slopes of about 3 to 4 feet of run for every 1 foot of rise. The peak of the berm should be positioned closer to one end instead of in the center of the berm and the top of the berm should be flat to prevent water from running off the sides of the slope. Rather than designing a perfect oval, you can have undulating tapered edges, multiple peaks or even a crescent shape.
Lay out the design for the berm on the ground with garden hoses the garden hoses flex easily so you can achieve curves and make design changes before fully committing to a design. After you are satisfied with the shape of the berm, you can transfer the outline to the turf with landscaping spray paint.
Remove the sod layer from inside the marked outline, using a spade or sod cutter to cut through the turf. You can leave the turf in place, if desired, but carving out the grass makes it easier to see your design as you build up the berm.
Add clean fill dirt to the inside of the berm design perimeter to build up the bulk of the berm. Spray the mound with a garden hose to moisten the soil and pack the soil down tightly. The fill dirt should account for about half the total height of the finished berm leave about 1 1/2 feet from the outline edges free of fill dirt to allow room for top soil. .
Cover the fill dirt with a few inches up to 1 foot of clay soil, depending on the total berm height in your plan. Make any final corrections in the berm shape with the clay layer. Although clay and fill dirt are not required, clay is often used because it sticks well and is less likely to erode after a heavy rain, which can affect the berm's shape.
Add topsoil over the clay layer to build up the remaining height for the berm.
Flatten the topsoil on top of the berm with a shovel so the berm doesn't form a pointed peak. Drag the topsoil with a bow rake down to the outer perimeter of the berm outline to achieve the necessary slope for the berm and smooth the edges. Pack the topsoil gently to hold it in place on the sides of the hill.
Place large flagstones and boulders throughout the berm to give the berm a more natural appearance. Bury one-third to one-half of each stone so the stones appear as natural fixtures on the hill.
Plant your choice of small trees, shrubs, perennial and annual flowers and groundcovers on the berm as soon as possible so the roots can take hold and anchor the soil in place on the sides of the slope. The top of the berm is a great location for showcasing short plants that often get lost when planted on flat ground. You can plant several trees at the top of the berm, but avoid planting in a straight line, which can appear unnatural. Medium-height plants and groundcovers work to fill in space on the sides of the slope and helps to keep soil from washing down the slope.
Add a 2- to 3-inch layer of mulch around plants on the berm. Mulches with irregular shapes, such as shredded bark, work best because the long pieces tend to lock together to resist washing down the slope.
A former cake decorator and competitive horticulturist, Amelia Allonsy is most at home in the kitchen or with her hands in the dirt. She received her Bachelor's degree from West Virginia University. Her work has been published in the San Francisco Chronicle and on other websites.
One of the most common mistakes in landscaping is creating earthworks that look contrived. Rigid, non-sinuous shapes stand out like a sore thumb in the midst of a larger lawn or garden. Berms too large cause many physical problems while those too small are clearly out of place. Your designer knows this and will consider the following criteria for a successful grading plan.
The slope of a berm should be gentle if it is to support plants and avoid problems with erosion. Height dictates the scale of the earthwork. You must calculate the horizontal distance up one side to reach the high point, then add the same distance to the other side to get back down to grade again. Added to this is the area at the top of the berm or mound that is not part of either slope. This three part calculation determines whether or not a berm of a designated height would fit in the space provided.
It is easy to underestimate how much fill is required to create earthworks because it loses volume when sufficiently compacted to ensure cohesiveness. The cost of trucking clean fill can be prohibitive. This is why most berms and mounds are far more cost effective on projects that generate fill onsite. The most common source is the excavation of building foundations, swimming pool or basement.
Mounds or berms must always be fully integrated with the grading and drainage plan for a homesite. These earthworks often exist to solve problems and protect homes during high water flood events. Berms are particularly important when used to force water to flow away from the homesite or toward key points just like a miniature levee. They are valuable where a homesite may sit adjacent to a drainage canal, ditch, dry wash, creek or river. Be particularly attentive to this when berms are added to an existing landscape as part of a remodel to avoid interference with the existing drainage system.
If you return to the golf course model you'll see that the bunkers along the edge of a fairway flow gracefully beneath their cover of turf grass. They are all positioned relative to one another. Some of these can be long berms that may be relatively straight or undulate. When used to solve problems, this shape is directly related to prevailing winds, southern exposures and undesirable views.
Non-linear mounds are often oval or in a kidney shape so that the forms can flow like a natural landform. In general, graded mounds used site-wide should be similar in scale and height to better integrate them into the overall character of the landscape. Low and wide on top is the mantra that ensures successful planting and irrigation.
The angle of repose is nothing more than the degree slope of a mound's edges. It is considered the same way as a roof, which is expressed as 4:12, which is four inches of rise over twelve inches of run. With mounds planted in turf grass, the maximum slope ratio is expressed in feet such as1:4, which means the slope goes up one foot over a four foot span. It is far better to strive for 1:5 or even less to ensure turf grass maintenance equipment can function safely, and the blades cut without scalping.
The most common mistake is making mounds and berms too steep to support plants. Overly steep sides cause water to run off before it can percolate into the soil. Insufficient saturation means the root ball easily dries out and is nearly impossible to re-wet again, particularly in hot, dry climates. Mounds planted with trees, shrubs and perennials should be graded as gently as possible, without exceeding a 1:4 ratio.
Experienced landscapers know exactly how to shape a mound so it looks attractive. In nature, very little is symmetrical, so creating mounds of irregular shape is always preferable. The top of the mound will have a high point, which is best set at one end or the other, and never ever in the center. Sculpt the high point to a flat top so that water applied there can soak in because all excess run off gathers at the toe in a perennial mud hole.
Photo: Total Landscape Care
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.
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.
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.