The Complete Guide to Boulder Retaining Walls and How They Can Save Your Landscape

How Much Does A Boulder Retaining Wall Cost?

Stone retaining walls can add a natural touch to your yard. Retaining walls hold soil in place, allowing you to build a flat patio, pool, or planting area on a slope. Medium to large boulders make excellent retaining walls that are both attractive and long-lasting.

A retaining wall will cost between $100 and $600 per ton of boulder rock. The cost varies depending on the type of rock you want as well as your location. Installing the wall will cost between $45 and $75 per hour. At $300 per ton of boulder, the average cost for a 25-foot-long wall is $5,000.

Whether you build the wall yourself or hire landscapers, paying attention to the details will ensure a long-lasting wall. Continue reading to learn how to build a boulder rock retaining wall, why some walls fail, and to get answers to any other questions you may have about these retaining walls.

What is a Boulder Retaining Wall?

A boulder retaining wall is a natural rock barrier made of natural boulders placed with their largest side into the soil. The stronger the wall, the deeper the stone side into the soil. The boulder rocks can range in size from a foot to six feet. Medium boulders are defined as being less than 2 feet in length.

How Much Does a Boulder Retaining Wall Cost?

An effective retaining wall is built on a gravel base that is 1-2 feet below the new wall’s height. The wall is built from the ground up and extends to the soil level. This allows water runoff to flow over the wall rather than up and through it.

The Cost of Boulder

Determine the length of the wall you want to build to determine the cost of your rock. Determine the width of the wall based on how much dirt the rock will support. Will it be one boulder wide or two to three boulders wide? Then decide on the height of the wall.

A two-foot visible wall should be one foot below the soil line. In this example, a 25-foot-long wall that is 2 feet above ground, 1 foot underground, and 2 feet wide requires 11.25 tons of 150-pound concrete. rock boulder

The formula:

150 cubic feet = 25 ft. long wall x 3 ft. high (2 ft. above ground, 1 ft. below ground) x 2 ft. wide
150 cu. 150 lbs. x ft. The weight of the boulder = 22,500 pounds
22,500 pounds divided by 2,000 pounds per ton = 11.25 tons

The Cost of Labor

Landscaper labor costs vary by region, averaging $45-75 per hour. It is possible that it is even higher in major metropolitan areas. A structural engineer may also be required to confirm the wall design. These cost between $125 and $250 per hour.

Costs of Removal and Excavation

A retaining wall is built in three stages: removals, excavations, and construction. A tree or fence may need to be removed. Then you must dig for the wall. A 2-ton mini excavator rents for $250-$400 per day.

Other Costs

Gravel costs about $30 per ton plus delivery. For sandy soils, you may need to use a geogrid to place the rock and filter fabric. Budget for any permits you may require, as well as visits from the power company to mark pipes and wires.

What are the Different Types of Boulder Retaining Walls?

1. Limestone

As a retaining wall, this option has several advantages. If durability is an issue, limestone can withstand intense forces such as soil movement. Your boulder retaining wall should last as long as possible, which is not a problem with limestone. We get limestone from eastern Wisconsin, which is much denser than limestone from Minnesota. When quarried, this material also has a more consistent shape, which adds to its aesthetic appeal.

2. Fieldstone

Fieldstone is an excellent choice for creating a natural, rustic look in your outdoor space. Fieldstone adds visual appeal and typically does not require adhesive material (such as mortar) to adhere together. Because it is also quite dense, these retaining walls have a rugged appearance when compared to other types of boulders.

3. Iron Range

If you’re concerned about the cost of installing a retaining wall, iron range is an excellent choice due to its low cost. While it has a similar appearance to limestone, this material is less expensive, making it a popular choice for large-scale projects. Because of the distinctive coloring of the iron range, it provides a distinct look to the backyard area with a natural appeal that many property owners adore.

What are the Benefits of Using a Boulder Retaining Wall?

A retaining wall not only adds height and dimension to your landscaping, but it is also an important part of any home’s foundation. The wall can keep your land from eroding, and if your home is built on a slope, a strong retaining wall can keep land from sliding away from the foundation and weakening it, damaging your landscaping, or both.

There are several common advantages to installing a retaining wall:

  • Make a decorative addition to your home.
  • Create garden beds.
  • Keep the soil moist and in place.
  • Direct rainwater away from your home, allow you to avoid major property damage.
  • Get rid of the eyesore of dirt piles, hills, and sink holes.
  • Reduce maintenance and protect against erosion.

The Best Ways to Use Boulders in Your Landscaping

Bye-bye, ordinary landscaping!

One of the most significant benefits of using natural stone boulders in your landscape is that they have the amazing effect of revealing nature’s pristine beauty. These large, stately landscaping stones can completely transform the look and feel of your property. They can also reduce the number of plants required while still providing a pleasing appearance. We believe that using boulders can help you be more creative with your landscape or garden design.

1. Begin with a strategy

If you intend to landscape with boulders, you should definitely plan ahead of time. Remember that boulders are difficult to move due to their considerable weight. If you are unsure how to move a boulder safely, consult a professional landscaper or the landscape supply yard where you purchased it.

As a result of their weight and the fact that they are natural focal points, you should place the boulders first. Also, keep in mind that using boulders will serve as a visual anchor. As a result, it’s a good idea to design your garden and other landscaping elements around your boulders.

You should also plan on sinking your boulders at least a few inches into the ground. This provides safety in the event that children decide to climb on and play around them. It also protects the boulders from shifting and putting stress on them, which could cause them to crack one day. And, from a design standpoint, they appear more natural. No massive rock protrudes from the dirt. They make themselves at home. Some designers will set them up to 25% below grade, depending on the size and weight of the stone and the soil composition. When arranging them in a dramatic position, it is sometimes best to place them on a gravel or concrete base.

2. Go for broke or go home!

When customers are in our landscape supply yard trying to decide which boulders to buy, one piece of advice we frequently give them is, “Don’t be afraid to go big.”

We frequently find that people viewing a boulder outside of the context of their property underestimate the size required. When they bring their rock home and place it, they frequently discover that it appears much smaller in relation to their home and landscape. As a result, we recommend selecting a boulder that appears to be a little too large. When placed in the context of their larger landscape, it is usually the correct size.

3. Include levels in your design

With such a wide range of sizes available, landscaping with boulders is the ideal medium for incorporating distinct levels into your design.

First, decide on the key areas of your space where you want to establish and develop levels. You can do this with raised beds, retaining walls (if you have sloped or hilly ground), or simply with rocks and greenery. By varying the dimensions of boulder groupings, you can define each level. Then, to further characterize each level, incorporate smaller landscape stones and greenery.

4. For a dramatic effect, use specialty boulders

You can use single boulders of varying mineral composition to create texture and color variation in your landscape or garden. You can also use texture or color groupings to add visual interest to an area. Your decision is frequently influenced by the shape of the rock. You might want blocky or angular stones for accents or features in one area of your garden and rolled, water-smoothed rocks in another.

5. Colors can be used to create a mood

To inspire the mood and feel of your design, select from peaceful off-white and ivory colored stones to striking black boulders, or from lively yellow and red hues to mellow gray or taupe shades highlighted by greens from lichen and moss. Boulders provide a surprisingly diverse range of color to complement your landscape. Because color influences our moods, you can use boulders to help you design areas of your garden or landscape that are either soothing or stimulating to enjoy.

Boulders with moss and lichen can also provide some interesting color options, including green, gold, gray, brown, and even some orange.

These brand new decorative landscape boulders are sure to catch your guests’ attention with their amazing, show-stopping color effect. These stunning pieces are naturally enhanced with sparkling mica mineral deposits and can provide eye-catching color and panache exactly where you want it. You can also create amazing centerpieces that are unique to your neighborhood or dazzling accents to make your landscape really stand out. These stunning natural stone colors are also ideal for accents, retaining walls, and water features.

6. Use different textures to add interest or accents

One can make use of the wide range of textures found in various types of boulders. There are many different textures to choose from, ranging from smooth and rounded to rough and angular. Weathered limestone boulders, mossy boulders, or boulders with lichen or other vegetation on them can all be used to add texture to your design.

7. For a dramatic effect, use landscape lighting

Boulders make excellent landscape lighting focal points. Experiment with various bulbs. A broad flood will produce a different effect than a narrow spot. Warmer lighting is generally used on boulders because it has a more natural feel, though this is a personal preference. Uplighting either the boulder or some features behind the boulder, such as a wall, tall grass, or a tree, can also produce some very nice effects.

8. Make a statement with boulder placement

If you want to achieve an Oriental feel, for example, use this design as a creative idea to achieve your goal. To emulate the tranquility of water, place a smooth, solitary white boulder in a designed setting of small smooth stones.

Alternatively, you can form and create the illusion of a waterfall by cascading your boulders down a slope. Even better, if you happen to have a stream or other water features in your landscape, you could use your boulders to create a waterfall.

And don’t underestimate the power of a single, lone boulder. A large boulder in the right spot can have a dramatic effect. If you’re unsure where to put it, go with your gut instinct. Your subconscious mind knows what appears natural and appropriate, so trust your instincts. After all, landscaping is all about evoking and arousing emotions.

9. Allow the style of your landscape and the characteristics of your boulders to guide their placement

A good rule to remember is that your landscape should serve and complement the beauty of your home. Your goal should be to create a design that unifies both aesthetics. When deciding which side of your boulder should face up or in a specific direction, consider the style and feel of your home and property. Allow your boulder’s shapes and dimensions to influence whether it should stand up, lie flat, or jut upward at an oblique angle. Take visual cues from your home’s style and appearance, as well as your landscape or garden, and then arrange your boulders accordingly.

While you’re at it, switch up the orientation of your boulders to add some variety. If all of your boulders are set upright or lying down, your landscape or garden may appear artificial or deliberate. This is not how nature appears. Some should be upright, while others should be laying down or leaning against another. Mixing it up makes it appear more natural.

10. Incorporate boulders into your rock garden ideas

The addition of boulders frequently inspires further design. Placing one, three, or five boulders in your rock garden, for example, gives it a mysterious feel. And, for some reason, it seems that using odd numbers of boulders works better. Many people notice that once the large stones are in place, a “flow” appears, and then adding landscaping with small boulders and gravels appears to happen more naturally. These stunning creations are inspiring an increasing number of people to experiment with rock landscaping in their front yards.

Landscape boulders add an air of permanence to your garden, making it a place where your gardening dreams are truly “cast in stone” with their fascinating shapes, subtle striking colors, and solidity.

How to Construct a Boulder Retaining Wall

The following are the steps for constructing a boulder retaining wall:

  • Take down any trees, fences, old walls, or concrete patios in the area.
  • Excavate down and back to make room for the gravel footing as well as the wall itself.
  • Lay 5″ deep gravel that is at least six inches wider than the boulders.
  • Lay a filter fabric along the bottom and back of the wall for sandy soils.
  • Lay a geogrid on the soil or filter fabric if using one.
  • Move the boulders into position with the excavator.
  • Place the large flat-sided boulders against the soil wall.
  • Shake the boulders with the excavator to ensure they are securely in place.

Soil Considerations for a Boulder Retaining Call

Whether or not you use a geogrid or filter fabric along the back of the boulder retaining wall is determined by the type of soil you have. The geogrid holds the soil in place, allowing the rocks to fit more securely. With sandy soil, the filter fabric is used to keep the soil from moving through the wall.

If the soil contains clay, don’t use a filter fabric because the water absorbed by the clay will fill up the fabric filter, causing it to bulge out and push the boulders forward.

How Long Do Boulder Retaining Walls Last?

A well-built boulder retaining wall should last for 30 years or more, as natural rock will last for years in the elements. The shape of the boulder retaining wall will be influenced by the rain and freezing cycles. If built properly, the wall can last much longer than 30 years.

What Causes Boulder Retaining Walls to Fail?

Most boulder retaining walls fail because they were built incorrectly. People who cut corners on properly excavating and preparing the footing will run into difficulties. Because the inside of the wall has more cracks and spaces for the soil to move against the rock, walls with the largest rock faces on the outside may be prone to shifting.

How High Can a Boulder Retaining Wall Be Built?

A boulder retaining wall can be built up to four feet high. A building permit may be required if the height exceeds four feet. If you want a wall taller than five feet, you’ll need an internal structure to keep everything safe.

Consider two or three tiers of boulder retaining walls if the height is greater than three to four feet. These tiers will allow for more planting, creating a lovely sight. Tiers are more visually appealing than a large wall.

More About Boulders

How Many Boulders Are in A Ton?

Of course, weights vary from rock to rock, so these are only rough averages.

  • A one-man boulder is a small landscape boulder, usually up to 12′′ in size. These little guys can weigh anywhere from 20 to 200 pounds or more.
  • A two-man boulder is typically up to 18′′ in height. These typically weigh between 150 and 500 pounds.
  • A three-man boulder can be up to 36 inches tall. So, how heavy is a 3-foot boulder? These beasts can weigh up to 800 pounds or more!

So, as you can see, the terms one-man, two-man, and three-man do not actually mean you can move these behemoths with people! When it comes to larger and heavier boulders, you will usually want professional equipment, shipping, and placement. It should also be noted that much larger boulders than these are still available. Click here to see an example of a large boulder being loaded by inexperienced people!

How Do You Move a Boulder?

Professionals will use a large truck, typically a flatbed. The boulders should be placed and strapped onto pallets so that they can be loaded with a forklift or a backhoe (depending on weight). When people use the wrong equipment to load and transport large boulders, bad things happen. You risk not only damaging your vehicles and loading equipment, but also putting people in danger.

Quick recap

A boulder retaining wall will provide you with a beautiful landscape piece that will last for many years. You can have a great retaining wall that is attractive, functional, and affordable whether you build it yourself or hire landscape professionals to do the work.