A hill is a wonderful natural playground for kids to scramble up, roll down and play hide-and-go-seek on, but when soil is piling up at the bottom or rain channels start to form down the sides, you know erosion is becoming a problem. Terracing—which is made of wide, shallow planting areas like steps down the side of a slope—is an effective solution to soil erosion. Brick, stone and concrete walls are some materials suitable for terrace walls, but treated timber is one of the easiest to work with. Alternatively, where erosion isn't severe, a selection of ground cover plants, shrubs and trees suitable for erosion control can prevent the soil being washed away. (Ref 1 and 2)
Contact utility companies to check there are no pipes or underground lines running through the slope. Check for these as you dig.
Measure the height of the hill and the distance along the slope from top to bottom. Calculate the number and depth of steps needed to terrace the hill. For example, if a hill is 10 feet high and the distance along the slope is 20 feet, five terraces 2 feet deep and 4 feet wide will cover the slope.
Dig a trench at the bottom of the slope to hold the first terrace wall. Dig deep enough to hold the wall foundations: For a timber wall less than two feet deep, dig down as deep as half your timber's thickness. Check that it's even throughout with a level.
Lay timber in the trench to build the first wall; use a staggered pattern for additional strength. Check levels again. Drill holes for stakes, then bang them into the ground with a mallet.
Dig a trench at the back of the first bed to hold the second wall. It should be as far back as the intended width of the terrace step, plus the width of the wall. Dig down to the same depth as the first trench. Check levels, insert timbers into the trench, drill and stake them in place. Move soil from the back to the front of the bed to create a flat planting area.
Build the front wall of the second terrace on top of the back wall of the first terrace. Drill the timbers and hammer spikes through to join both sets of timber. Dig a trench at the back of the second terrace to the depth of its front wall and construct a back wall. Continue constructing terrace steps up the slope.
Work from the top of the hill downward when planting, and water plants before moving on to the next terrace in order to avoid stepping on newly-planted areas.
Dig planting holes for plants and mix soil with an equal part of garden compost, leaf mold or well-rotted manure, before planting. Set shrubs and large plants vertically in the soil, not at a right angle to slope, and put ground cover and small plants flat against the hillside. Fill in the gaps around the roots with soil and compost mixture and to set the plants firmly in place.
Dig a shallow trench in front of plant stems to help retain water as it flows down the slope, then water thoroughly.
Spread a mulch, such as shredded bark, vineyard mulch or mixed fir bark, across the slope. Water regularly so that the ground is moist, but not sodden, throughout the first year as plants develop.