using pot elevators is a great idea where you want to ensure maximum air pruning and never want your roots to touch a dirty common bench. Dr Coco uses a similar double saucer method to catch the leachate in the bottom most saucer just to measure leachate pH and ppms before that waste is drained off. It is indeed a brilliant concept. Professor Carl Whitcomb designed a stepped pyramid air pruning 4 inch pot in the late 1980s that is probably the most optimal small container ever designed. When a 4 inch roots hits air and burns back, branch roots erupt along the previous 4 inches and create a fibrous non circling root system. As much as one may be tempted to use a deeper pot with the same design, Whitcomb points out that if an 8 inch deep were used instead of a 4 inch pots that all this root branching would occur in the bottom 4 inches of the 8 inch pot and the upper 4 inches would not be exploited until the lower zone were first filled with roots. This is one reason growers generally get better results by transplanting up at least one or 2 times during the whole grow.
Even the common use of fabric grow bags employs the principles of either root trapping and/or air pruning to great advantage. I love air pruning and first employed the use of mesh bags in the early 1980s, before the nonwoven bags were even commercially available. This sub irrigation method is simply another approach to root pruning and moisture control in the container media. It does run extra risk of inviting a root rot pathogen, but there are several ways to mitigate or even eliminate these potential pathogens. There are at least 2 commercially available sub watering systems that many cannabis growers use. The AutoPot and the OctaPot. The AutoPot design hinges on these clever 2 stage float valve that allows a 1 inch deep container to completely drain or 1/16 inch layer of water left before the vaccuum pressure is broken on the lower valve and the reservoir then floods till the upper float valve mechanism shuts of the water level. The OctaPot manual system has a floating stick gauge that alerts the grower when the water has dropped into the red zone and then grower adds water. The automated version employs a tall feed solution reservoir which constantly tops off a Master Float reservoir which then feeds all the individual plant saucers which flood to the level that the master reservoir is flooded. Super cheap mini floats for $5 can be also be used for individual saucers in a DIY scenario. Hundreds of youtube videos on DIY versions of self watering planters exist. Some containers employ a suspended mesh deck above a reservoir and use a capillary mat or wick of some kind to lift the water to the plant root base Capillary matting has upper flow limits and for plants that use a lot of water such as cannabis and tomatoes. Others use media substrate feet that extend into the reservoir to wick water up, One could also set a fabric bag filled with media and both the bag and the media will wick up the water. If most of the bag sitting in water is too water saturated and you wish more air flow, the fabric bag can be lowered onto an inverted mesh pot which will lift the center of the bag above the water line allow for increased drainage and air exchange while the perimeter of the bag descends back into the solution. There are dozens of tweaks to these scenarios, but it is possible to engineer a system in which the vertical wicking of water is highly controlled and even the choice of media can ensure optimal levels of water and air throughout the profile. Using a gradient of particle sizes and a choice of hydrophobic or hydrophillic properties it is entirely possible to create a soil space where water and air are more evenly distributed than in any system where a container filled with either a single component or a homogenous mix fills the entire container. A 60/40 mix may overall have optimal airspace starting 2 inches above the bottom of the pot, but it may be slightly too dry for the upper 3 inches of the media. I am just making these numbers up, but i am going to use a laboratory grade moisture probe to actually measure the WHC at various depths in the media. I am going to speculate that if the bottom 3 inches of the container used a water absorbing coarser material with fewer fines that airspace would improve in the lower part of the container and that the upper dry zone of the container could be made wetter by using a finer particle size material. Of course, such a layer cake gradient media fill would almost certainly require only sub watering because any abrupt soil layer will at least temporarily perch water at each boundary interface as water drains downward from a top watering. Even coarse gravel over sand will temporarily flood the entire gravel zone before the water begins to seep into the sand. I know this sounds counter intuitive but i have read dozens of papers and seen dozens of actual demonstrations in clear pots where this fact of physics was proven repeatedly.
So, you are correct that there is no runoff in this system. In fact i use a constant or near constant water level to WATER root prune instead of AIR prune. One can also use entrapment or constriction to root prune or heat prune or chemical prune such as using copper hydroxide treated nursery pots, copper mesh, a concentrated peroxide solution which literally oxidizes the root surfaces that it contacts. Manually pruning is also exploited but the tearing injuries to plant tissue is an open invitation to invading organisms
If too many roots grow through the bag and become water roots but i need to transplant up into a larger pot, rather than tear off the roots, i would either drain the water then air prune or chemical prune the roots with a stronger solution of
hydrogen peroxide so entry points of infection would be reduced.
Large orchards grown on drained swamp land use control boards on field canals to control the water table height. Some of these systems date back over 200 years. Your mother may have watered her clay pot by simply adding water to the saucer, tand commercially available Wicking pots have been available for over 2 decades. some Kratky methods grow an entire crop floating on a single reservoir of never replenished water. So it is possible, I have grown thousands of pots of pampas grass, tomatos, beets and chard in 3 to 6 month long experiments as well going back over 30 years. For a crop cycle that is often less than 3 months, a sub irrigated system is almost fool proof.
A recirculating system will contaminate all plants where a sub irrigated system will only contaminate those plants which share a reservoir. Any pathogen or algae can be handled using a proactive bio control, or ozonated water or
hydrogen peroxide just poured into the saucer to control any algae. Any commercial grow that uses recirculated water needs to provide bio designed filtration plus inline UV, ozone or peroxide injection or some similar type technologies.
I just harvested a plant that was 1 year 9 months old just to see how long it would last before any damage. I finally got what appears to be a slow dropping of leaves and indeed there is some soft rot starting on the lower trunk where the "bark was cracked and wounded" when i was wrangling the 4 foot plant around that was stuck in the scrog grid.
For those people who find themselves manually watering 10 to 14 x a day, if they put a saucer under the plant, the runoff water will be used up in under an hour, but they may only have to water 8x a day but there would be zero waste if you wanted. However any wet dry irrigation cycling in a sub watered system increase the risk of drowning Moist Air or Terrestrial roots. When these white roots die back, discolor and begin to rot and at the very least some saprophytic organism is now consuming this dead tissue. Some rhizosphere product in the sub water may insure that a more beneficial organism is doing the feeding because even an out of control pathogenic bacteria or fungi can result in a pathological consequence for a dead root and the host plant. Outright pathogens such as Pythium or Fusarium if introduced will most certainly lead to death if not mitigated in some fashion.
The most probable way of introducing a root rot pathogen in a sub watered system is by letting the reservoir dry out. When this happens roots will grow to bottom of pot and then potentially drown upon a future flooding ... although many cannabis strains can adapt and grow more hydro like roots. If you start with a pathogen free media, you can easily outlast a 12 week window, if you keep the individual plant reservoir constantly or cyclically flooded frequently enough. You use the water to prune or discourage the roots continuously, Only those roots whose morphology convert to grow hydro will venture into the area. For plants that hate wet feet these roots will simply never grow into the overly saturated zone. Now to compensate for this PWT Perched Water Table or Saturated zone simply increase the height of the pot by at least the depth of the water level or better still to the height of the water level plus the perched water table level in the media. For an example lets say you are using a coco media without sub irrigation and if you used an accurate enough water moisture probe determined that the bottom 2 inches of the coco was overly wet everytime you watered but since it drains fast enough and cannabis is vigorous enough, it usually worked out but still NOT OPTIMAL. Now lets say you use a taller grow bag by 2 inches like a 12 inch tall bag vs a 10 inch bag. In the 10 inch bag, there is 8 inches of more favorably conditioned media but in the 12 inch bag there is still a 10 inch depth of not overly saturated soil for the roots to explore. many growers hate tall pots, the plants fall over and they have to water more often than the same volume of substrate in a shallower container. Growers adapt to their materials and environments as well and since cannabis is a vigorous grower, whatever works for people is something they will probably just keep doing, but it may or may not be scientifically optimal or some other issues may have to be adjusted for or compensated for.
People can grow in straight water. Of course lettuce can grow in static water with Dissolved Oxygen aka DO as low as 1/2 part per million. As
oxygen in the atmosphere is about 20.3%, the partial pressure of
oxygen at sea level (1 atm) is 0.203 atm. Thus the amount of dissolved
oxygen at 100% saturation at sea
level at 20° C is 9.03 mg/L . Even with air bubblers it is difficult to exceed 13 percent but under some lab conditions using venturis or ozone injection or peroxide this can be upped supposedly to 50 ppm. Standard DO instruments top out at 20 ppm whereas regular air is 200,000 ppm oxygen. Even the most poorly drained greenhouse media is probably at least close to 10% Airspace = 100,000 ppm oxygen so even using an airstone under a regular fabric pot in a drain to waste will probably lead to increase yields when someone actually tests it out. Let us imagine a grower using a pot size and mix where he waters once every 3 days, chances are the mix is really too wet for the entire first day so an airstone below the bag might provide optimal o2 immediately but many only need to run for 4 to 8 hours. This is a future experiment on my task list. A simpler solution is too place and inverted pot in the center of the bag before filling with media. Professor Kratky use a full gallon pot upside down for this but loved my idea of using an inverted Mesh cup {optimal size to be determined] sleeved in pantyhose to provide even greater Air Flow and eliminating the zone in the container where the media always verges on being overly wet. I just kicking out some observations on the whole water Air space interaction and many viable approaches and tweaks. Sorry to run on so long
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