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Old June 1, 2013   #8
SIP Gro-Tubs
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Join Date: May 2013
Location: Natalia, TX
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Quote:
Originally Posted by rwsacto View Post
Thanks for the detail. Just to summarize (for my understanding) You have large drainage holes in the bucket wall above the shelf, overflow holes in the bucket wall below the shelf and no aeration/drainage holes in the shelf.

Yes. but since around the edge of shelf is not sealed to the container walls, you will have drainage if needed. But that is the area were there is less water from the wick, compared to the center of the container. Once the moisture from the wick spreads out laterally from the wick, and the soil near the wick gets to the same saturation point as the wick. The wick will stop wicking.


Its the same as how your own blood system works.

My understanding of container aeration is to provide oxygen exchange through diffusion at or near the bottom for the roots to breathe and to prevent anaerobic conditions in the media that will kill roots. Yes, you understand partially. If aeration is to be effective it needs to be in a upward movement thru-out the whole media column in a continous flow, un-restricted to push the CO2 and other harfull gases out the top of the media, to the underside of the leaf canopy, so the leaves can use it.

But you have major Restrictions in your design:

1. Covering the top of the media with plastic sheeting.
2. Size of the particles of media, to the amount of void between the particles.
3. Water collecting in the voids between the media particles, since your using a basket to wick water.



Diffusion does not require "force" (moving air or water) to happen. It is driven by the difference of partial pressure Yes, you just explained the force that you call ( difference of partial pressure.)

What do you think the ( difference of partial pressure ) would be in a enclosed container with 3" depth of water, 5 gls, with a 1" deep air gap above the water, since the water is in a dark confined space it would be relatively cool, cool doesn't rise like hot does, so the air in the air gap just sits there with out any force being applied to it.

(in this case) oxygen in the air and in the media (gas as well as dissolved in the water). Yes and No, As soon as water under pressure is exposed to air thats not under pressure, the dissolved O2 gases will dissipate out of the water, into the air gap.

An example of this action is the same as if you pour a soda into a glass, the CO2 will diffuse out of the soda, amd become flat in a very short time.

Diffusion will try to equalize the partial pressures. As the roots and bacteria in the media use oxygen, Yes, and they need lots of it to have a healthy enviroment, but remember at the same time they are expelling CO2, which makes a un-healthy enviroment, the same as you. And you want the CO2 to flow upward to be used by the plants leaves, YES.

more will flow from the air into the media through the top of the media NO, you've blocked that action with the plastic, thus trapping the CO2 in the media, and the plastic is a restriction of O2 moving upwards.

or through the aeration holes. NO, you've blocked that action also with the plastic, on top and by over saturation of water from the wick basket. So now you have filled the voids between soil particles with liguid water instead of keeping just the soil particles moist, leaving the voids free to diffuse gases upwards.

In your design, I believe what you call drainage holes are performing as the aeration holes. YES & NO. In my systems, I, don't use plastic top coverings. The holes are there for excess water from rain and a nearby sprinkler system. I, use a cedar shreded fiber mulch instead on top. Also the fertilizer is mixed into the bottom 2/3 of the containers, not laid on top. So the idea that un-composted mulch robs the nitrogen is False.

Therefore, your design works without holes in the shelf. YES. Since the polyester wick doesn't wick as fast as a soil wick would, causing the voids between the media particles be filled with liquid water. The media particles in my system are the extended wicks, leaving the voids empty between media particles.

A bit of aeration is probably also happening through the fiber wicks. NO, since the O2 dissipates as a gas out of standing water, same as CO2 out of a opened soda. The wick is just transporting water moisture, not what most people think as water coming from a pressurized hose, its not the same.

In Earthtainers and similar designs with no holes in the container walls and where the shelf is positioned above the overflow holes, I believe the holes in the shelf act as both drainage holes and aeration holes. The only reason you would need drainage is if the media mix is saturated with water. And since bottom watering has been proven to be the best watering system of any contanerized system compared to top watering. Thats why "Wick hysroponic" systems are one of the best for sub irriagatted planters. But if you don't follow the design, it won't work properly.

Without aeration (in the bucket wall or the shelf) I believe the SIP will still wick water fine, but the bottom will get stinky and the plants will perform poorly. NO, if your media mix is designed for sub-irriagation, the media won't get stinky, soggy, or past the moisture point, to support a anerobic enviroment.


The shelf in a 5 gl bucket has 86.5 square inches.

Drilling 40 holes, 3/16" dia, would produce a total of 1.1 sq inches for aeration, or 1.28% of the shelf area.

Drilling 40 holes, 1/4" dia, would produce a total of 2.0 sq inches for aeration, or 2.3% of the shelf area.

Drilling 6 holes 7/8" dia. in the side of a 5 gl bucket, for a total of 3.6 sq inches of area for aeration.
But with those 6 holes, I can increase the aeration of the media to 70.6 sq inches, using a "Worm Hole design"

The shelf in a 30 gl tote has 390 sq inches.

With 100 drilled 3/16" holes would produce 2.75 sq inches of area for aeration, or 0.7% of the total shelf area for aeration.

With 100 drilled 1/4" holes would produce 4.9 sq inches of area for aeration, or 1.3% of the total shelf area for aeration.

With 6 drilled 7/8" holes thru the outside of the tote would still produce 3.6 sq inches of aeration, but with my "Worm Hole design" that will increase the total aeration in contact with the media to 132 sq inches for aeration, or 37 times more than drilling holes in the shelf.


Terry Layman
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