No problem, these things can be made any dimension… but the basic premise lies in the nature of how water wicks.
Water’s nature is to be bonded thru charge – First, your reservoir needs to have free water. That means that the water must have an area free of it’s physical attachments or at least less encumbered by it. If water is bonded to something… the wicking capacity is diminished. An open source- in this case the standard drain field tube allows this as well as gives a large port for filling. Ideally there should be a space of air between the water and the dirt. This allows better suction for the wick.
Second, the water needs to be in direct contact with the soil in order to wick. For this we provided Eco-felt stapled to the reservoir in a draping fashion- like a W. The drain field tube is in the center and the two sides are filled on top of the Eco-felt with soil. Water is in direct contact- but the soil and water do not mix which is important over time. This also allows for the addition of earthworms in a completely contained system where the unit and reservoir are the same dimension. Earthworms love the water- but they can drowned if they are unable to find a way out- So we use the Eco-felt or septic drain liner to separate the free water source.
Finally, you need to be aware of what you will be planting. Water only wicks a max of about 12 inches and the closer to this height it is- the less moist the soil will be. The is good essentially because you want the most water to be at the appropriate parts of the root structure. The taller your reservoir, the lower your soil wicking ability becomes as your reservoir drains. So, as an example… If you have a 12” bed with a 4” reservoir and you let the reservoir get down to 1”depth- your soil will only be wicking to 9”. If you have a bed depth of 12” and a reservoir of 6” and the reservoir gets down to 1”- you will only be wicking 7”. This is the most basic formula, but can be applied to any situation based on what you are planting. A standard formula for wicking is 12” including the reservoir- Earthbox is- I believe- is 9” with a reservoir of almost 3”. If you are planting root crops- you want a large soil area so that you don’t get rot. When you start from seed you may have to topwater for a bit until the plants get started. If you are transplanting- say tomatoes- you always set them deep and remove the lower stems anyways, so usually topwatering is minimal.
The first bed is a completely enclosed system 15’ x 4’ x 1’ with the same size reservoir @ 2x4 depth with a taper down to 6”. The system was mainly intended for larger crops- corn , okra, eggplant- which once established can feed from this depth. The one in the latest pictures is 12’ x 3’x 1’ deep and a 16” x 8’ reservoir set in the center@ 2x4 depth with a taper down to 6” in the middle. We used this depth because we knew this bed would be used solely for large plants- bananas and papaya- so again the wicking did not need to reach the uppermost part of the bed. In addition, this bed is an open system- the bananas can essentially grow thru the open part of the bed an into the ground soil, but will still receive benefits from the wicking at the base of the bed.
This last bed took four bags of black cow, four bags of peat moss, six 50 pound bags of worm castings, 5 lil bags of pearlite and the leftover dirt mix from 10 wicking boxes we already had mixed up. The soil is the expensive part.
Hope this helps.