Edible Forest Garden : filling missing layers and functions

Design

Plan of the Edible Forest Garden. New trees are in color, existing trees are in black, trees to remove in gray. Nitrogen fixers are in blue, fruit trees in green, and pest control trees in orange. Deep rooted trees have dotted background, and persistent trees have a double border. Shrubs, or mulch trees to keep as a shrub, are star shaped.

The forest garden as we see it would extend through the whole garden, mixed with vegetable beds, with sunny or shady patches here and there, but we focused on a location to start from, not too far and not too near to the planned house (zone 2-3). In this location, we decided to keep most fruit trees, but we planned to remove few of the too many almond trees we have. We designed the edible forest garden plantation such as to optimize the use of sun light, shade from the wind, improve soil root partitioning, fill the tree, shrub, vine and lower layers, protect from insects and provide fertility with nitrogen fixers.

Planting

The plan at the right summarize the design and plantations.

1. We planted tall (e.g. carob, walnut) and shade tolerant (e.g. guava ) trees behind short and sun loving trees, e.g. grapefruit, kumquat (see section plan above). We also intermixed deciduous and persistent trees to distribute sunlight available in winter.
   

   Section of the forest garden, and relative position of the winter sun

2. Wind tolerant trees, especially for maritime exposure (e.g. caroub, pistacia atlantica, peruvian pepper), were planted at the north limit, the direction of the prevailing wind. On the long term, they would replace the cypress trees as wind break, while providing more functions in the garden (e.g. food, fertilization, pest control)
3. To optimize root soil use, we tried to keep a distance of plantation providing 1.5 adult crown size around each tree, but our garden has already so many trees we often planted with less than this distance. Additionally, we planted preferably shallow rooted trees (e.g. grapefruit, persimmons) near to deep rooted fruit tree (e.g. fig). While most fruit trees are shallow rooted (e.g. plum, almond, citrus, olive, mulberry), but most legume trees or shrubs are deep rooted (e.g. albizia, caroub, gleditsia, moon trefoil, ), which is practical for partitioning soil when interplanting shallow rooted fruit trees with deep rooted legume trees or shrubs. Allelopathic plants (e.g. walnut) was buffered with tolerant plants (e.g. mulberry, gleditsia) to prevent its negative effect.
4. 

   We see in this photos the layers in our forest garden, from annual herbaceous (e.g. beans, broadbeans) to shrubs (e.g. sage, leucaena), to small trees (e.g. kumquat), to large existing trees behind (e.g. almond, plum), growing on the double dug swale

   Tree layer in our garden is already well populated with mostly Prunus spp (e.g. plum, almond and apricot) that share the same illnesses. In the tree layer we wanted to diversify. We marked some almond tree for removal, and placed new different trees (e.g. citrus, guava, pear, walnut). The shrub layer was almost inexistant. We interplanted the trees with shrubs, using mostly nitrogen fixer shrubs (e.g. albizia, moon trefoil) but also aromatics (e.g. atriplex, sage, rosemary, laurel) and ornamental edibles (e.g. carissa, acca, eugenia). This layer requires a large number of shrubs, and is still under progress. The vine layer was originally partly occupied with grapes and wild asparagus We tied the grapes to help them climb existing trees. We also planted few brambles, but only one survived. In Tunisia planting vegetable under fruit trees is very common practice. Indeed, stacking permaculture designs, we built special beds (see previous article) for herbaceous, root crops and ground cover layers, and planted both annuals or biennials (e.g. tomatoes. pepper, potatoes, celery, parsley, spinach, legumes) and perennials (e.g. artichoke, chicory, sweet potatoes, strawberry)

5. For pest control, we planted few trees (e.g. peruvian pepper, melia azedarach) among the fruit trees, to act as a repellent for pests. The limited choice of available edible shrubs in Tunisia led us to use many aromatics (e.g. rosemary, sage, marjoram), that we believe will act as pest control for both trees and planting beds under them.
6. For fertility, we planted nitrogen fixing trees (e.g. gleditsia, caroub), shrubs (e.g. albizia, moon trefoil) as well as lower layers (e.g. alfalfa, broadbean, peas, clover, chickpeas). Legume trees and shrubs were placed between fruit trees, as mentioned earlier. Some legume trees (e.g. albizia) have been planted as mulch trees, will be coppiced often and will keep a shrub size.

When trees were placed, we used this opportunity to add mycorrhizal organisms to the root and compost to inoculate the surface. The plan show the initial part of the work, we extended, along the year, following the same pattern with more fruit and legume trees (e.g. strawberry tree, ziziphus, myrtle, judas tree, leucaena).