At our farm, after the lasagna bed we previously reported, we experimented with bed permaculture designs : double digging, hugelkultur, mulches, patterns, swales. We built several of these beds during a workshop we organized at the farm with Permaculture Tunisian Association, a group we made with other tunisian permaculturists.
We experimented the “double-digging” method for our new swale. With this method we conserve the top soil on top during the earthworks, especially important as we cultivate the mound and the trench of the swale. That means that we remove the topsoil in pieces then we modify the bed profile and then put back the topsoil. In this way we preserve the soil structure and mechanisms while providing aeration of the soil. This bed proved to be very productive when planted with vegetables, but this method is time consuming in comparison to simple earthworks.
After the first Hugelkultur wood buried bed we built to break the clay (see our previous article), we made two new ones. We’ve built a second version of hugelkultur or wood stuffed raised bed with a friend, Zied. In a part of the garden with very shallow sandy soil, we buried acacia trunks (top right photo). Then we added mycelium from the nearby forest, and covered with the soil of the path around the bed and and mulched with straw. This bed is one of our favorite, as vegetables look to thrive, due to the improvement of soil depth and water retention. After some months some non-identified mushrooms appeared. The third hugelkultur bed, we built it recently in a workshop with permaculture association members. We wanted bigger trunks for longer fertility, like Sepp Holzer’s, but in our climate large trunks are hard to find. We got a fallen tree from the forest and buried it entirely. We are eager to see the result.
Petal pattern beds
We built a planting bed in a petal pattern around a mulberry tree. This permaculture design access to all part of the tree for harvesting its fruits while allow to cultivate under the tree and prevent soil compaction on tree root. This bed was constructed during the workshop.
We tested different type of mulches and in particular chipped rameal wood (CRW) & straw. These mulch reduced radically the evaporation and helped seeds to germinate and seedlings to survive in our dry climate. For woodchips, we tested mostly olive tree, that we chipped, and tried in various configurations: with or without leaves, fresh olive vs. old pine, with or without cardboard underneath, and mixed or not with the top soil.
Mulches we tested were good for preventing weeds germination, especially with cardboard, but when mixed with the topsoil weed prevention was low. Even our seeds or very small seedlings had hard time to survive on thick mulches, while large seeds (e.g. chickpea, lupin, broadbean) were more able to germinate through the mulch. Mulches also had good moisture preservation and evaporation limiting effect. Mulches , especially woodchips without leaves, but even packed straw, was efficient to keep moisture when the layer is thick enough. With 10 cm thick mulch layer, the soil is still wet one week after irrigation in the hot dry Tunisian summer (40°C). As we expected nitrogen fixation by the mulch, we mostly only planted legume plants (chickpeas, lupin), but the onions we placed there did also good. However, two problems with mulch was that wild boar & slug were attracted by the wet conditions and damaged the beds and the plants, and disrupted the mulches.
We built a mandala circular keyhole path – one keyhole in the center and circular path around. We micro terraced each part with sones, the slope was only 10cm. Then we planted with chickpeas and mulched the hole. Chickpea did grow nice, but we noticed that the ground cover nitrogen accumulator Stellaria was thriving in these conditions, suggesting that soil was full of nitrogen from chickpea air fixation and terraces construction soil disturbance. We noticed that wild boar loves chickpeas, and he damaged the soil and plants in this area extensively.