Perched water table is only relevant to excessively capillary media, media lacking sufficient aeration, or very young plants with little root mass.
Otherwise, it's rather irrelevant. It's just more water for an established plant to take up, and it's not preventing any gas exchanges.
hi, afka! "Perched water table is only relevant to excessively capillary media," such as coco, perlite, rockwool, peat, pine bark, turface, de, small lava rock, sand, gravel, rice hulls or hydroton. using any of these media the pwt will be relevant. i suppose there are some media choices where it may not be relevant, but for most commonly used media it is.
containers are not the open soil column and create an artificial set of conditions for the plant to cope with. one of these is the pwt.
most gardeners are forced to use the above mentioned media in various combinations because they, in addition to decent air porosity, must have decent water retention.
media that has pore spaces too large to support a pwt will have extremely low water retention, requiring more frequent watering events.
a pwt or saturated layer does indeed present a barrier to gas flow while it exists. not to molecular flow, but to gas flow.
again, the elimination of the pwt from the root chamber is but one of the design elements of the ppk.
traditional gardening using containers and the media listed above works good if you are an experienced gardener and know when to water. most of these new growers have never grown a plant before and all over the internet forums you see posts from folks having plant problems of all sorts.
this device instantly turns these people into successful growers of there own medicine.
let's go back to the basic scenario where the gardener waters the plant by hand. how is this decision made? most use the "lift the pot, you'll get a feel for it" method. when it feels light water it.
what happens during this process? immediately after watering there is formed a pwt. this represents a raising of the water level typically between 1-2" in most media.
since the last watering "air" type roots have grown down into the area. research has shown that this can occur in as little as 12 hours. these root structures are not designed to sit in standing water as are the "water" roots. so they begin to drown. the only reason they don't drown completely is that the gardener doesn't water too often. you guys all know that smell of rotten eggs. that's evidence of drowning and dying root material. this takes experience to manage. new people are usually not very good at it and suffer the consequences.
here is a little basic math for you. a 5 gal bucket is approx 10.5" in diameter. the typical pwt using most media will average around 1.5". 3.1416 x r2 x (depth in inches) 1.5 = 129.88 / 231 (cubic inches in a gal) = .562 gal. so about a half gal with most conventional media.
now take a 1.5" id tube. same math gets you .011 gal. from al's statement and many research papers we know that the pwt will exist at the same height in any size or shape container regardless of volume. this is due to the media characteristics, not anything to do with the container. this is why traditional plant containers are all taller than they are wide. this is a design effort to reduce the pwt. also tapered pots help.
by using the 1.5" tube passing through an air gap sufficiently sized to contain the pwt we are reducing the volume of the pwt to only 2% of what it would be if we did not. this frees pot space for "air" type roots and prevents "stalls". the effect on the plant is dramatic.
the idea of controlling and reducing the pwt has been around for a long time. patents and applications are full of attempts to do just this so it has long been recognized as a problem inherent in container growing.
ok, enough of the pwt and minimizing it. lets look at the other side of the problem. the plant. the "dry your pot down between watering events" evolved to deal with the pwt in containers. if you are fertigating you are constantly running salts through the medium. when you allow the medium to dry you are concentrating salts. this causes buildup. this is another commonly recognized phenomena as evidenced by the use of products like dripclean. watering to a certain amount of run off is another way to control it.
but there is another, more insidious side to this. a side that limits plant growth. that is because plants can't take up nutrients without the presence of water. they also can't assimilate nutrients that are in excessive concentrations.
so why not build a device that eliminates the pwt from the root chamber, thereby eliminating the need to reduce watering to keep from drowning the plant yet at the same time allowing you to provide water and nutrients with mass availability, accelerating growth?
while we are at it let's add a reservoir under the plant so that the plant is "fooled" into behaving as if the container is much larger by providing a hydraulic pathway all the way through it.
there is much more to all this, of course, and i'm sure you are all great gardeners and grow beautiful plants.
but you will grow larger, higher yielding plants if you deal with these issues.
well, that's all for now. i'm tired.
d9
