In our garden we have experimented with different kind of mulching and lasagna beds and now, after some time, we have a better idea on how this permaculture technique works.
In theory: from mulching and composting to lasagna
Lasagna gardening is a no-dig, no-till organic gardening method of building the garden by adding layers of organic materials before planting that will “cook down” over time, resulting in rich soil. Inspired by natural forest processes of soil building, permaculture simplest version of lasagna gardening is sheet mulching technique. The simplest model for sheet mulching consists of the following steps:
1. The soil is covered with a thin layer of slowly decomposing material (known as the weed barrier), typically cardboard. It suppresses the weeds by blocking sunlight, increases the mechanical stability of the growing medium, and adds nutrients to the soil as weeds quickly decay beneath the barrier.
2. A layer (around 10 cm thick) of weed-free compost or soil rich in nutrients is added, in an attempt to mimic the humus of the forest.
3. A layer (at most 15 cm thick) of weed-free mulch, woody and leafy matter is added in an attempt to mimic the forest floor surface or O Horizon. A mulch is a layer of material applied to the surface of an area of soil with main purpose to conserve moisture, to improve fertility and to reduce weed growth.
Lasagna gardening, based in the same principle, offer a short and long term source of nutriments to the plants by embedding in place cold composting process. In lasagna gardening, layers of organic materials are inserted to sheet mulching steps between the cardboard and compost layers (between step 1 & 2). These layers alternate nitrogen rich (i.e. low C:N ratio) and carbon rich (i.e. high C:N ratio). The top layer of mulch keeps the bed humid warm and beautiful!
In november, we built two raised beds with lasagna method to improve the soil fertility and increase the its depth.
- To make the first bed, we placed over a new raised bed clipped oxalis and pine needles as nitrogen and carbon rich four layers, we covered with compost and homemade (but not weed free) compost, and then we mulched with wood chips of decomposing barks from forest. We planted in this bed just after construction with beans, chard and beet seedlings, and later peas and tomato.
- To build the second bed, we made several layers in these steps: weed clippings, pine needles, vegetable scraps, acacia dry leaves, vegetable scraps, cardboard, compost, cardboard and straw. We planted also this bed just after construction with chickpeas, broccoli, celery, spinach and cabbages seedlings.
After earthworks, but before lasagna.
Grass clippings and pine needles layers.
Wood chips mulch layer
At first, the seedlings planted on the lasagna beds were growing very slowly. Some of them spent the winter in a slow motion growth. Some months later, in early spring they started growing nicely and finally we harvested a lot of vegetables: chard, peas, parsley and tomatoes.
We had though losses due to slugs in winter, that loved living in the straw mulch and eating the seedlings. We managed to save them from slugs by placing them under cloches, after trying beer traps, Artemisia mulch and night hunt. Weeds from the compost were also a concern in the first bed that was quite quickly invaded, but not in the second bed, that stayed weed free until today due to the double layer of cardboard we used. We also experimented with different mulches on our different garden beds: wood chips, straw, wild plants cuttings, Artemisia against slugs, cypress needles against grasses germination.
The lasagna beds are very nice once installed and the plants seem to be comfortable in there, but It’s better though to wait few months that decomposition is advanced before planting, for instance, make them in autumn and plant them in spring. Time of preparation can important if materials are not available in place or need processing (e.g. chipping). Soil profile of the beds is important to keep the materials in place, as a flat bed is better than a round bed, as materials slide down with rain water, animals or wind.
Kids love lasagna
We used lasagna technique to prepare gardening beds with kids in the Bardo cultural center, in Tunis with the Association ‘Citoyenneté et Environnement’. Firstly the kids designed the shape of the beds directly on the area. They created small islands beds. Then they added successively layers cardboard, wet green clippings, dry woody material we found in the garden and cow manure, then covered with straw and pine needles as mulch layer. The activity was ludic and allowed them to learn how they can use the organic matter of the garden. At the end, they planted mustards, broad beans, onions, broccoli and mint plants and watered abundantly.
The final aspect of the beds is very nice small garden beds. However, it could be better if the kids plan the shape of the garden firstly on paper. The material was prepared in advance, though when needed the kids helped and enjoyed gathering materials from all around the garden for their lasagna. Months later, we were surprised to find the beds keeping their shape with few plants that has grown with only few weeds, with no maintenance and no watering at all.