Quote:
Originally Posted by FinnBar
capillary action will occur no matter what height to diameter ratio. the bigger the diameter, the greater the evaporation speed.
Ray states on his site that he has previously used all kinds of containers, painters buckets and whatnot, so if you want to make your own, there's nothing stopping you.
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This is an interesting issue (well, to me anyway). First, I'm not sure that capillary action is the main mass transfer mechanism at play here. In theory that would require a continuous capillary to move through. Obviously with individual clay beads we have no such continuous path internally though you may argue that external clay surfaces provide a path that adhesion and surface tension could exploit similarly to a tube.
There is clearly a height factor involved in capillary transfer. The maximum height that a liquid can be lifted through a tube with round cross section is 2 x surface tension divided by the product of the liquid density x the radius of the tube x acceleration due to gravity (32 ft/sec/sec). If external surfaces are being used as capillaries then some similar, but complex, mathematical solution would apply. In short height is a factor.
I suspect that evaporation from the reservoir and condensation on higher beads as the vapor rises is a more likely mass transfer mechanism in SH culture. In this case the more evaporation that occurs from the top surface the better. That is because as water vapor leaves the container more evaporation occurs below and there is a continuous rise of moisture through repeated evaporation and condensation steps as we go upwards. Of couse this means more frequent need to add liquid to the container. This mechanism suggests that no restriction on height applies because the vapor will rise until it reaches the surface and leaves the area.
In conclusion to this boring solo, I suggest that both a form of external (to the clay beads) capillary action and evaporation/condensation is at work here. Since the capillary mechanism is height limited, there probably is a sweet spot for the proper container height. There is also an advantage to larger container surface areas, but that is not operable outside the root diameter.
So the best container is a diameter that contains, but does not exceed greatly, the plant root ball diameter. The proper height is one that provides continuous moisture to the roots through both mass transfer mechanisms above and allows a reservoir area below the main root ball. I do not pretend to be able to calculate the dimensions of this container, but I do suggest that an optimum exists. Since Ray has done some experiments to support his container and medium recommendations, it appears smart to stick closely to his geometry until you have data other than his to support changes. Thus I repeat my conclusion that approximately a 2:1 height to diameter is proven workable and deviations should be considered carefully.
Jim
how tall pots?
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