Terracing
Part of Farming Basics
Flat land is a luxury that most communities will not have. Hillsides make up a large portion of usable land worldwide, but farming a slope without terracing is an exercise in watching your topsoil wash away. Terraces convert steep, erosion-prone slopes into a staircase of level growing platforms that hold water, hold soil, and produce reliable harvests for generations.
Why Terracing Is Non-Negotiable on Slopes
When rain hits a bare slope, water accelerates downhill. At just 5% slope, runoff velocity doubles compared to flat ground. At 15%, water moves fast enough to carry away topsoil — the thin, nutrient-rich layer that took centuries to form. A single heavy rainstorm on an unterraced 20% slope can remove 1-2 cm of topsoil. In five years, you are farming subsoil. In ten, you are farming rock.
Terracing stops this by converting one long slope into many short level platforms. Each terrace:
- Slows water to zero velocity on the flat growing surface, forcing it to soak in rather than run off
- Traps sediment behind the terrace wall, gradually building deeper, richer soil
- Creates a controllable irrigation path — water moves from upper terrace to lower terrace in a predictable, manageable way
- Reduces the effective slope from whatever the hillside grade is to nearly flat on each platform
Types of Terraces
Bench Terraces (Full Cut-and-Fill)
The most effective type. You cut into the hillside and use the excavated earth to build up the outer edge, creating a completely flat platform.
| Slope Grade | Terrace Width | Wall Height | Effort Level |
|---|---|---|---|
| 10-15% | 3-5 meters | 0.5-1.0 m | Moderate |
| 15-25% | 2-3 meters | 1.0-1.5 m | High |
| 25-40% | 1.5-2.0 meters | 1.5-2.5 m | Very high |
| 40%+ | 1.0-1.5 meters | 2.0-3.0 m | Extreme — consider if worthwhile |
When to use: Where you need maximum growing area and have labor to invest. Best for permanent agriculture sites where the community will farm for decades.
Contour Bund Terraces (Low-Effort)
Simple earthen ridges (bunds) built along the contour of a slope. Not fully leveled — the ground between bunds remains slightly sloped but water is intercepted by each bund and forced to soak in.
When to use: Where labor is limited, slopes are moderate (under 15%), and you need quick erosion control. Good as a first step while planning full bench terraces.
Stone Wall Terraces
The terrace wall is built from dry-stacked stone rather than earth. Extremely durable — properly built stone terraces last centuries without maintenance.
When to use: Where stone is abundant on-site (rocky hillsides often provide their own building material) and earth is too shallow or loose to form stable bunds.
Building Bench Terraces: Step by Step
Survey and Mark
Step 1. Build an A-frame level. Lash two straight poles (2 meters each) together at the top to form an A shape. Tie a plumb line (string with a stone weight) from the apex. When the string hangs centered between the legs, both feet are at the same elevation. This tool is your contour finder.
Step 2. Starting at one end of the slope, place one foot of the A-frame on the ground and pivot the other foot uphill or downhill until the plumb line reads level. Mark this point with a stake. Continue across the slope, placing stakes every 2-3 meters. The line of stakes marks one contour — one terrace location.
Step 3. Move up the slope by the desired terrace width (typically 2-4 meters of vertical rise between terraces, depending on slope) and repeat the contouring process to mark the next terrace.
Step 4. Mark all terraces before digging. Stand back and verify the spacing looks reasonable and the contour lines follow the natural shape of the hillside. Adjust if needed.
Excavation
Step 5. Starting at the back (uphill edge) of each terrace, dig soil and move it toward the front (downhill edge). The goal is to create a level platform by cutting into the high side and filling the low side.
Step 6. Excavate to the depth of topsoil first — set the dark topsoil aside. Then move the lighter subsoil forward to build up the front edge. Finally, spread the reserved topsoil over the entire leveled surface. This ensures your growing surface has the best soil, not buried subsoil.
Step 7. Compact the fill edge firmly. Walk on it, tamp it with a flat rock or log, and let it settle with one or two rains before trusting it with heavy use.
Slope Stability
On slopes steeper than 25%, the outer (fill) edge of a terrace can collapse, especially when saturated with water. Reinforce the outer edge with a retaining wall — even a low one (30-50 cm) of dry-stacked stone dramatically increases stability. On very steep slopes (35%+), stone retaining walls are mandatory, not optional.
Building the Retaining Wall
Step 8. If using stone, select flat-sided stones and stack them without mortar (dry-stack). Tilt each stone slightly inward (toward the hillside) — a wall that leans into the slope at 10-15 degrees from vertical is far more stable than a perfectly vertical wall.
Step 9. Build the wall on a foundation trench dug 15-20 cm below the terrace surface. This prevents the bottom course from sliding outward.
Step 10. For walls over 1 meter high, include “through stones” — long stones that extend from the front face into the fill behind, tying the wall to the earth mass. Place one through stone per square meter of wall face.
Step 11. Leave small gaps (2-3 cm) between stones near the base of the wall. These act as weep holes, allowing excess water to drain through rather than building pressure behind the wall that could cause collapse.
Water Management
Step 12. Give each terrace a very slight backward slope (1-2%) — the growing surface should tilt slightly toward the hillside, not toward the outer edge. This directs water toward the back of the terrace where it soaks in against the cut bank rather than running over the front wall.
Step 13. Build a small drainage channel along the back edge of each terrace where it meets the cut bank. This channel catches water seeping from above and directs it to the terrace ends rather than flooding the growing surface.
Step 14. At each end of the terrace, build a spillway — a reinforced, stone-lined section where excess water can flow safely from one terrace level to the next. Without spillways, overflow water finds the weakest point in the wall and erodes a breach.
Never Block All Drainage
A terrace that traps water with no outlet becomes a pond during heavy rain. The saturated soil becomes heavy, the wall fails, and the collapse cascades down the hillside taking every terrace below with it. Always provide controlled overflow paths.
Vegetative Reinforcement
Living plants are the best long-term stabilizers for terrace walls and edges.
| Plant | Role | Where to Plant |
|---|---|---|
| Vetiver grass | Deep roots (3+ meters) bind soil; dense above-ground growth filters sediment | Along the outer edge of each terrace, in a continuous row |
| Leucaena/legume trees | Nitrogen fixation, deep roots stabilize slope above terraces | Along the back cut bank |
| Sweet potato | Dense ground cover prevents surface erosion on terrace surface | On the growing platform as a crop |
| Napier/elephant grass | Massive root system holds terrace edges; stems provide animal fodder | Terrace risers (the vertical face between levels) |
| Banana/plantain | Large roots stabilize soil, broad leaves reduce rain impact | Terrace ends, spillway margins |
Plant vetiver or a similar grass along every terrace edge within the first season. By the second year, the root network will be strong enough to hold the terrace even if the stonework shifts or the earthen bund erodes.
Maintenance Schedule
| Frequency | Task |
|---|---|
| After every heavy rain | Walk each terrace, inspect walls for bulging/cracking, clear debris from spillways |
| Monthly during rainy season | Check drainage channels for blockage, repair any erosion on riser faces |
| Annually (dry season) | Rebuild any collapsed wall sections, re-level growing surfaces that have developed ruts, clear vegetation from spillways |
| Every 3-5 years | Full inspection of all retaining walls, replace worn through-stones, add soil to terraces that have compacted or subsided |
Calculating Labor and Time
Terracing is labor-intensive. Plan realistically.
| Task | Labor (person-hours per meter of terrace length) |
|---|---|
| Survey and marking | 0.5 |
| Excavation (hand tools, moderate slope) | 4-8 |
| Excavation (hand tools, steep slope) | 8-15 |
| Stone wall construction (1m high) | 3-5 |
| Stone wall construction (2m high) | 8-12 |
| Planting vegetative reinforcement | 0.5-1 |
| Total for a 10m bench terrace on moderate slope | 40-80 person-hours |
A team of 5 people can build one 10-meter bench terrace per week. For a small hillside farm (0.25 hectare), expect 3-6 months of construction work. This is a multi-generational investment — those terraces will produce food for centuries if maintained.
Common Mistakes
- Building on the contour by eye. Even small errors in level cause water to pool at one end of a terrace and overflow, creating erosion. Always use an A-frame level or water level, never eyeball it.
- Making terraces too narrow on steep slopes. A 1-meter-wide terrace is barely usable. If the slope requires terraces narrower than 1.5 meters, consider whether the site is worth the investment, or use the terraces for tree crops that need less working width.
- Neglecting spillways. The most common cause of terrace failure. Every terrace must have a controlled overflow path reinforced with stone, or the first major storm will breach the weakest wall section.
- Building during the rainy season. Freshly excavated soil is vulnerable to erosion. Build during the dry season and plant vegetative reinforcement immediately so roots establish before the rains arrive.
- Forgetting topsoil preservation. If you bury topsoil under subsoil fill, your terrace surface is infertile. Always strip and set aside topsoil, then replace it on top after leveling.
- Vertical retaining walls. A wall that does not lean into the hillside will eventually be pushed outward by soil pressure and collapse. Maintain a 10-15 degree inward tilt on all retaining walls.
Key Takeaways
- Any slope over 5% benefits from terracing; over 15%, terracing is essential to prevent topsoil loss
- Use an A-frame level to find true contour lines — never estimate by eye
- Cut from the high side and fill the low side; always preserve topsoil by stripping it first and replacing it on top
- Every terrace needs a controlled spillway for overflow — blocked drainage causes catastrophic wall failure
- Tilt retaining walls 10-15 degrees into the hillside and include weep holes for drainage
- Plant vetiver grass or similar deep-rooted species along every terrace edge in the first season
- Terraces are a multi-generational investment: weeks to build, centuries of productive use
- Inspect after every heavy rain and repair immediately — a small breach becomes a total collapse if ignored