By creating a sort of “reservoir” under the soil modeled after earth boxes, our plants can take up as much water as they want, when they want it.
Hard to believe, but the natural occurrence of rain falling from above is not always ideal. If it comes at the wrong time, or in too much quantity, it can cause molds, inhibit pollination, and actually creates conditions that are not ideal for plants to uptake water.
Plants have a hard time extracting water and nutrients from saturated soil because there are no air pockets. From here there are 3 levels of water uptake that plants notice. They can easily uptake from the coarse soil material, when the easy pickins are gone, they start uptaking from finer soil particles, but this is a little more difficult for them. Finally, they are left with only very fine soil particles with water left in them, and while this water is difficult for the plant to extract, they will not die. In nature plants may see all four the these conditions in transition. During a heavy rainfall they get saturated and must wait for that to drain, and then transition through the 3 stages.
What our growboxes provide for the plant is all four conditions…at the same time, so that they can always grow at their maximum potential. The bottom is saturated as it is literally in the water reservoir. Water wicks up, and it creates a moisture gradient ending with dry soil on the surface, creating a natural evaporation barrier. Plants will generally set as deep of roots as necessary for their optimal uptake, and our 24 inch deep beds accomodate most of our veggies, and allow for us to practice bio-intensive farming.
Our beds are 20 ft x 5 ft, and 2 ft deep and made of 2 inch lumber. They are lined with 45 mil rubber, and the ends are plumbed with custom bulkhead fittings.
Once rubber is in and the ends are sealed, a layer of pumice rock lines the bottom.
Over the pumice, we put a layer of landscaping cloth which allows water transfer, but keeps the soil separate from the pumice. We created a custom cross-section of pumice that always allows a pocket of air under the soil, even when the reservoir if full (the high peak down the center is higher than the water line). And low points ensure that the soil is in contact with the water down to 1 inch of water.
Nutrient rich water from our aquaponics system is pumped into one end of the bed, and the water comes out clear on the other end. The reservoir is now full, and soil will wick up water feeding the veggies.