Definition: A type of permagarden bed established 10-15 cm below the surface of the ground to trap runoff and increase moisture retention.
Sunken Beds in the Forest Garden:
Sunken beds help collect and retain moisture in a permagarden bed. They are generally preferred by farmers in the Forest Garden Program that live in arid conditions.
To prepare a sunken bed, farmers remove the topsoil layer of a bed and place it to the side. They then remove another 30-40 cm of subsoil. The next layer of subsoil is then loosened, the topsoil is amended and placed on top of that, following the principles of double digging. After completing this process, farmers are left with a bed that is roughly 10-15 cm below the surface of the ground. Farmers should assess the water flow of the permagarden area and use small trenches redirect it into the beds, where it will penetrate into the soil. Mulching should also be practiced, to reduce evaporation and retain soil moisture.
While the benefits of sunken beds can be significant, they also come with challenges. It is critical that the soil is not compacted when reapplying the amended topsoil through double digging as this will impair plants’ root development.
Another challenge can arise in the rainy season as these beds can become water-logged in soils with poor drainage. If drainage is a problem in an area with significant rain events, farmers need to monitor the permagarden following rains and potentially remove standing water to avoid drowning their crops.