Swales – Ditches with a Difference

Digging swales and building berms (Photo: Libby Crichton/PSN)

One of the mantras you will often hear in permaculture is: “The best place to store water is in the soil.” Swales are one important way we can do this.

Swales are ditches dug along the contours (the parts of a slope that are on the same level) of the land to catch and hold water. Instead of allowing rainwater to flow down and over the top of the land, often washing the fertile topsoil away with it, swales trap water and direct it deeper into the soil so it can slowly infiltrate into the land. This helps to build healthier soil and plants, which further reduces erosion, and can regenerate entire landscapes and increase resilience to drought.

A series of swales and berms can be built on a massive scale across farmland, or on a small scale in any garden with a slope.

When a ditch is dug, the soil is piled up on the downward side of the swale, and this mound or ‘berm’ is planted with trees and other perennials plants that will be watered by the swale.

If you want to build swales, remember to start preparing the berm before the ditch is dug. Treat it like a no-dig garden – start with a layer of cardboard and newspaper as a sheet mulch to inhibit weeds, then add layers of compostable materials, before the top soil from the swale is added.

Swales are commonly used in food forests where fruit trees and other edibles are planted into the berms.

Small swales in an urban garden are often filled with pebbles, rocks, bits of old brick, and topped with wood mulch – materials that still will allow water to flow in, help keep the shape of the swale, and stop people falling in!