Retaining walls and terracing

How steep is too steep

Grass establishes from seed on gentle slopes without trouble. As a rule of thumb, slopes steeper than about 1 in 3 (roughly 33%, or 18°) are hard to mow safely and lose seed and soil in the first heavy rain. On those, either break the slope into level terraces or plant something other than lawn.

Options

• Terraces: a series of level or gently sloping steps, each held by a low wall of timber, stone or blocks.
• A retaining wall: one taller wall that creates a larger level area. Walls above about 1 m (3 ft) usually need engineering, drainage behind them and, in many places, a permit.
• Erosion-control netting and turf: on moderate banks, laying sod pegged down, or seeding through biodegradable netting, holds the surface until roots take over.

Do it before the lawn

Walls change the levels the rest of the job depends on. Build them after drainage and before topsoil and seed, and give every wall a way for water behind it to escape, or pressure builds and the wall moves.