Permaculture has a principle that states: the problem is the solution. When planting trees in areas where soil is almost all sand (especially in arid climates where evaporation exceeds precipitation and the soil is almost all alkaline) we can use the sand as water storage. Two holes are dug in sequence:
-First a hole of 5-10 feet (apprx.) is dug and lined with a water proof liner (plastic or e.p.d.m.)
-After hole is lined – fill the hole back up with the same sand that was excavated (this will serve as a water catchment barrier between the sun and infiltrated water for long term water retention)
-A smaller hole is then dug in the sand and that hole is then filled with a large amount of organic matter and mulches. A sapling tree can now be planted. Dynamic accumulators such as comfrey and vetches around the tree as ground cover will aid in shade, condensation trapping, and soil building.
Dave Jacke recommended adding a shelf to the bottom of this design which can be the base of water retention. Above the shelf an overflow can be installed (for lengthy rain events) eliminating the possibility of drowning plants and trees. Dave Catino recommended adding hugelkulture into the deep part of the shelf for further water storage. A large stone can also be added under the tree for a myriad of benefits, learn more here .
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