You can hold back the earth with attractive and easy to build structures. Simple retaining walls, without mortar and footings, can be as beautiful as they are functional in the landscape.
What is a retaining wall? A retaining wall is a wall purposely built for holding back soil on a slope, controlling erosion, or for aiding drainage.
Besides adding beauty and form to the landscape, retaining walls can also give you new planting areas or raised beds where improved soil and drainage allow more plants to grow.
Retaining wall can serve as dramatic accents themselves and act as transitional areas from ground level to tall shrubs and trees.
When considering a retaining wall, decide where the wall will best fit your needs, to hold an existing slop or support a new planting area filled with soil. The best approach for stability is to build the wall slightly out from the slope and backfill, rather than cutting into existing hillsides.
Consider the course of the wall; straight versus curved, and choose materials to suit the design and construction. Rock and modular walls can be built curved or straight, without mortar, and from a variety of materials. Wood walls offer stability, clean, sharp angles and blend well with decks and wooden homes.
Stable walls start with a well-prepared foundation. A shallow trench wider than the wall itself holds a base on which the wall is built. Typically, for a wall without mortar, a base of compacted gravel or stone walls is as wide as the wall is tall. For walls built on flat ground or for wooden or masonry walls, the trench and base should be level.
Walls of rock or pre-formed blocks should be sloped progressively inward with each level for stability. When using railway sleepers or timbers, anchor stacked timbers with steel rods.
To build a dry rock wall you will need: rocks of assorted sizes, hose, shovel, gravel and loose soil.
1. Lay rocks for the wall out on the ground according to size. Use a hose to wash rocks, removing any loose soil or grit from their surfaces.
2. Dig and level a trench 40cm deep, 8 cm wider than the widest stones. Fill with 20cm of gravel. Place the largest stones on top of the gravel.
3. Position the next layer of rocks. Pieces should fit snugly. The wall should gently slope into the hillside (3-5cm for every 30cm high).
4. Backfill behind the rocks with gravel and then soil. Insert soil into the gaps in the rocks for stability and along the face to use as planting pockets.
Where a lot of runoff is expected, leave spaces, or weep holes, backfilled with gravel, between rocks or timbers for drainage. Or, place perforated drain pipes, parallel with the soil, directly behind the rocks or timbers, then backfill around the pipes.
To build a modular wall you will require 12 modular base units, 6 modular cap units and 24 locking pins. Adjust these amounts to suit the size of your retaining wall.
1. Dig and level a shallow trench as deep and as wide as the units. Install base units side by side. Lock in with the pins.
2. Continue fitting the next level so each unit overlaps two lower units and is secured by the locking pins.
3. Add the cap units to the top. Fit these into pins from the previous row for a smooth finish.
Winter is a good time of year to undertake any ‘hard’ landscaping chores, such as building retaining wall. Dormant plants can be moved easily.
In spring, when the wall has been completed it can be planted, including pocket plantings or rockery plants or ground covers.
In summer, heat absorbed by or reflected off the wall can create hot conditions for nearby plants. Check and water plants in packets of the wall and at the base.
