How to Level a Sloping Garden

• First, measure the rise and run of your garden's slope. Then determine how many 2 feet (0.61 m)-high and 5 feet (1.5 m)-long terraces you'll need.
• Dig shallow trenches horizontally along the base of the slope. Put wall material into the trenches and ground them with spikes.
• Remove soil in between each wall until the soil is flat and add compost to the soil if you're worried about erosion.

Readying the Area to be Levelled

Contact local authorities to avoid issues with wires or building codes. Before you begin digging around your property, you’ll need to make sure there are no underground utility wires nearby that you might be disrupting. Get in touch with your local utility companies to make sure there are no underground wires your project may interfere with. You should also contact your local government agency responsible for city planning to confirm that your project will be in line with local building codes. In the United States, you can be put in touch with your local utility companies by calling 811. When you call 811, you’ll be connected to an operator who will evaluate your project and contact the relevant utility companies in your area so they can confirm the locations of underground utility infrastructure on your property. Although your project may seem small, many areas have bylaws and codes that specifically apply to garden terraces.

Measure the rise and run of your garden. Determine the vertical distance of your yard from the top to the bottom of the slope (the rise), as well as its horizontal distance (the run), by pounding a wooden stake into the ground at the top of the slope and a second stake at the bottom. Tie a string around the first stake at ground level, pull it taut, and tie it to the second stake in a place where the string is completely level. The length of the string is the run of your garden and the distance between the string’s location on the second stake and the ground is the rise. Place a line level in the middle of the string once you’ve tied it to the second stake to ensure that it’s level. Move the string up and down on the second stake until you’ve made it completely level to make sure you’re correctly measuring your garden’s rise and run. If your garden or yard has areas where the steepness of the slope changes, repeat this process in those areas to make sure you build terraces that level your garden at its steepest.

Calculate how many terraces you’ll need to build. Use the rise and run of your garden to calculate the number of terraces you’ll need to level it while maintaining each terrace’s structural integrity. Aim to have each terrace be no higher than 2 feet (0.61 m) and no longer than 5 feet (1.5 m) for best results. For example, if the vertical distance of your garden is 8 feet (2.4 m) and its horizontal distance is 20 feet (6.1 m), then you’ll need to build 4 terraces, each terrace being 2 feet (0.61 m) tall and 5 feet (1.5 m) long. Depending on the materials you use for your wall, as well as the steepness of your garden, you may want to build terraces that are longer than 5 feet (1.5 m) or taller than 2 feet (0.61 m). Although this is certainly possible, note that the risk of terrace walls bulging or collapsing tends to increase when they’re built to be longer or taller than these respective measurements.

Mark the areas where you will level your sloping garden. Once you've calculated how many terraces you'll need to build, you'll need to determine where they will be physically located. Mark off sections of your garden that correspond to the desired length and width of your terraces using little flags or stakes with strings tied between them to designate the areas you’ll be working in. Marking these areas will help you to avoid accidentally digging where you may not want to. It may be helpful to draw the intended locations of your terraces on a sheet of paper before actually marking off these areas in your garden.

Dampen the soil 24 hours before beginning to dig to soften it. You don’t need to soak it until it becomes muddy. You’ll just want to soften the soil up a bit before you begin digging into it. You can also wait until the day after a rainstorm to start digging, if you’d rather not pour water on the ground yourself.

Building the Terrace Walls

Opt for timber terrace walls to save money. Timber is a good choice for building shorter terrace walls on a budget, as it’s relatively inexpensive. Timber is also a nice complement to houses or backyards with a more rustic appearance. You can buy prefabricated wooden terrace walls at many home department stores or buy timber and cut it yourself from a lumber supply store.

Choose stone or concrete for your walls if you plan to make them tall. Stone and concrete blocks are popular materials for building terrace walls more than 2 feet (0.61 m) tall because of their strength. Although building terrace walls to be higher than 2 feet (0.61 m) is generally not recommended, definitely use stone or concrete materials to build your walls if you can’t avoid building them this high. Stone or concrete should always be used for terrace walls higher than 4 feet (1.2 m) and should be installed by professionals to ensure their structural integrity. These blocks can be bought at home and garden shop or landscape supply yard. Note that stone and concrete are the most expensive materials to be used for building terrace walls.

Dig a shallow trench along the horizontal base of the slope. Dig the trench so that it is slightly wider than the material you’ll use to build your wall. You should dig it wide enough to leave roughly 1 inch (2.5 cm) of space on either side of the wall. The depth of the trench will depend on which material your wall is made out of. Follow the manufacturer’s instructions to determine the ideal depth of your trench. If the ideal depth of the trench is unclear, a good rule of thumb when using timber is to bury the wall to about half of its thickness.

Place your wall material in the trench. Make sure that the terrace wall does not come up to more than 2 feet (0.61 m) above ground level (unless you’re using strong stone or concrete blocks). If the wall stands at a tilt, take it out and level out the bottom of the trench, then reinsert the wall.

Repeat this process to install walls along the sides of the terrace. The bottoms of the side trenches must be equal in depth and width to the first trench. Make sure all of the trenches are equally levelled.

Drive spikes or piping through the walls to stabilize them if possible. If the wall is made of timber, drill holes through the part of it that is below ground level. Then, pound spikes or pipes through it and into the surrounding soil to help keep the wall in place. Repeat this process for all the walls you’ve installed so far. For best results, use a pipe that is at least 18 inches (46 cm) long. If you’re using stone blocks or another heavy material to build your terrace wall, you can probably skip this step.

Flattening and Finishing the Terrace

Move soil from the rear of the terrace to the front. Fill in the rear side of the terrace wall trench with the soil. Then, redistribute soil across the terrace until it is uniformly level. You can use a small gardening spade to move the soil around if your terrace is not too large. For the trench you dug at the bottom of your garden, you’ll also need to fill in the front side of the terrace wall trench.

Remove soil from the terrace as needed until it’s flat. Place excess soil aside and flatten out the remaining soil until the terrace is level. Place a bubble level on top of the soil to ensure that it is completely level. If you plan to build additional terraces for your garden, you can use the excess soil from the first terrace to flatten out the next one.

Add compost to the soil to improve water retention. If you’re particularly concerned about erosion of your soil, take time while the soil is loose to mix some compost into it. Pour 2 inches (5.1 cm) of compost onto your soil, then use a tiller to till it into the soil for roughly 6 inches (15 cm) to 8 inches (20 cm). This will not only strengthen your soil, but will also provide it with healthy nutrients that will help the plants in your garden to grow.

Build additional terraces if necessary. If the slope of your garden is too steep for just one terrace, you may need to construct more than one terrace. Repeat this process as necessary until you’ve reached the desired slope for your garden.

Compact the soil in the upper terraces with a soil compactor. If the soil in the terraces next to your house is too loose, it may weaken the structural integrity of the terrace walls over time. To avoid this, use a soil compactor to compact the underlying soil and remove oxygen and any empty space. Make 2-3 passes over the terrace to ensure it’s properly compacted. Make sure the soil is sufficiently damp before beginning the compacting process. To test this, take up a clump of soil in your hand and squeeze it together. If the clump stays together, the soil is ready to be compacted. If it doesn’t stay together, dampen the soil a little before beginning. You can use a hand-held soil compactor or rent a power compactor from a local hardware store.