© 2008 by Raymond Alexander Kukkee
“How You can turn that ordinary retaining wall project into fabulous rock garden”
Dry Stone: Build a Retaining wall Rock Garden
The decision to build a retaining wall project into a rock garden is a spectacular opportunity to create a landscape accent that is not only functional, but aesthetically pleasing and unique.
Stone can be many colours, textures, and shapes; natural stone can be nothing less than exotic in appearance. Decorative possibilities are endless and the unique characteristics of each stone invoke a distinctive, natural, and one-of-a-kind look . Natural stone walls with ivies and other plants growing on them can provide phenomenally beautiful curb appeal to your property.
There are several advantages to building a retaining wall using the dry-stack, also known as the drystone building method. Retaining walls built of dry-stacked rock do not require a foundation, or concrete footing below frost penetration as a block, or stone and mortar wall require because drystone walls are flexible in nature. You can leave gaps in the face of the wall for plantings of ivies and other plants if desired. The walls will not crack, but settle naturally if at all. No unusual or specific skills are required; a drystack stone wall is within the reach of the average fit DIY’er with persistence and work.
Good design of any retaining wall and careful pre-planning can prevent expensive remedial action at a later date. Essential considerations for retaining walls built of stone are similar to structural requirements of other retaining walls. The most important structural requirements are drainage, height, stability, and reinforcement if the wall is higher or holding back a steep slope.
All retaining walls require the careful management of drainage. Excessive movement of water through a dry-stacked stone wall can be allowed under some conditions if the wall is well built, but movement of water underneath a wall of any kind will destabilize the structure, causing settling and perhaps eventual failure. Keep in mind that groundwater may also contain a high iron content, and will stain light coloured rocks such as limestone if the water is allowed to seep through the face of the wall.
The correct and logical solution is to install free-draining gravel, crushed rock or agglomerate backfill immediately behind the stone structure to allow vertical drainage, rather than through the face of the wall.
With natural stone retaining walls being so heavy, height limitations are of primary concern. Ideally, the lower the better. Logically, a 2′ high retaining wall stone wall is far less likely to fail than a 4′ wall. When incorporating a rock garden into a retaining wall, take advantage of the useable flat areas that can be landscaped between two 2′ vertical walls instead.
The extreme weight of a stone wall provides stability if the rocks are bedded properly . Consider the soil conditions and plan the design carefully to maximize the stability of the retaining wall. Simple and logical considerations include placing the largest rocks on the bottom, sloping the wall in as it rises, and avoiding the use of rounded rock. For the most vertical components, choose rocks that have two flat surfaces to maximize stability when stacked. The width of the base of stone walls should be one-half of the height of the wall.
For a higher wall, reinforcement may include deadmen stones, long stones that are built into the wall, the extending ends buried on the uphill side to help support the wall. Alternative possibilities include mechanical supports such as galvanized steel mesh, geogrid webbing, or galvanized deadman cables mechanically fastened to bedrock or larger anchor rocks buried in stable soil uphill.
Tools and Equipment and Supplies Required :
A mason’s’ hammer, rock hammer and sledge hammer
Shovel and pick, or alternatively the use of a hydraulic backhoe/excavator
Line level and Carpenter’s line
Carpenter’s 4′ level , a laser level, or transit level.
Gravel or free-draining agglomerate and crushed rock
Topsoil, bushes, ivies and plants as desired.
Rocks “Flatter types are easier to work with” Safety Gear: **As required on construction sites!
** Note: When working with rock, particularly using rock chisels, hammers, sledges and cutters, always wear eye protection, leather gloves, and steel-toed safety boots. Be smart and use all safety protocol on construction projects and sites. Protect passers-by and observers–particularly curious children.
Extremely large rocks are difficult to move by hand, but for stability, bigger is better. For maximum durability, you may also choose harder varieties of stone, such as granites , diabase, gneiss, or diorite if suitable stones are available, but in practice, limestone and slates, or various sandstones and schists, are generally layered, flatter, and are quite a lot easier to lay and cut if necessary. Natural, flattened stones of many varieties are suitable.
Each project is unique, but you can use this general process to build a dry-stack retaining wall, which is a mortarless structure and NOT generally intended for walls over 3′ in height unless built by highly skilled workmen.
1. Establish the location of the wall by installing a row of pickets.
Observe lot lines, any applicable bylaws in your jurisdiction, and digging and building permits as required. Do check with local electrical, telephone and cable authorities for buried lines and cables if you are working on the street side.
2. Excavate the footing area, to level, removing all soft, organic soil down to hard mineral soil. It is ideal if the first course of rock is partially buried in undisturbed soil.
3. If the trench bottom remains soft, install a 12″ layer of crushed rock for stability and tamp or compact it. Use a powered plate packer if available; rent one if necessary.
4. Install a carpenter’s line and pickets if the face is to be straight. Install the first course of rock level from end to end using the largest, flattest rocks available for the best stability. Tilt the rocks slightly toward the back for additional wall strength.
5. Install a perforated weeping tile on the uphill side level with the bottom of the rock course, and cover it with 4-6″ of crushed rock. Ensure the holes face down to ensure water entering the pipes does not fill them up with soil! Ensure the ends are positioned to allow water drainage from the pipe. Partially flatten the ends vertically and wedge them between the two end rocks, leaving it set back from the face to disguise the location of the pipe. Note that a pipe may not be necessary if the wall is backfilled with adequately free-draining material and the wall is established on crushed rock.
6. Install the second course of stone. Stagger the joints, remembering the mason’s rule of “one over two, two over one” for maximum strength. Chip off, or shim the rock appropriately to ensure maximum stability. DO set the second course back about an inch, and preferably, and again, lean the rock slightly back. If a rock does not set firmly and solidly in place, turn it over, or try a different one!
7. Back fill the rock courses with free-draining gravel, crushed rock or agglomerate for a horizontal foot behind the wall for drainage. Doing so will prevent water from seeping through the wall and staining the rocks.
8. Install subsequent courses as required, considering reinforcing as noted above if necessary, and the final height of the finished wall. The last course of cap stones should be as large, heavy, flat and stable as possible. Fit the capstones as tightly as possible, trimming them if necessary.
9. Back fill the wall with subsoil, compact it and place subsoil wherever required to achieve the grade desired.
10. For the extended rock garden, start at the retaining wall, and work up hill. Place rocks flat-lying or vertically, but randomly, on the subsequent sub-horizontal slope, leaving “holes” for plantings. Do use irregular sizes for maximum appeal, place large accent rocks, patches of coarse cobbles, rows of smooth river rocks, or decorative crystalline centerpiece rocks such as amethyst for visual bling if desired, ensuring you bed them solidly in a hole as necessary for stability .
11. This is how you can turn that ordinary retaining wall project into fabulous rock garden. Plant ivies, juniper, Mugho pines, perennials, and flowers of all types into the holes and gaps remaining as desired. In gaps on the vertical wall, Lobelia, strawberry, or other plants, include wild grape or ivies for a distinguished, vine-covered, old-world look.
Now you will not only have a retaining wall and rock garden that will stop the erosion of the landscape, but you will have a functional, beautiful –even spectacular accent for your yard –and may even have less grass to cut.
Is that Incoming I hear?