Working semihidroponic terracota

[Orchidcork]

After done some semihidropic for Catasetum , all details in the paper, i am working now in a semidroponic for Cattleyas, what are in the last 2 pics, still in crude
I would like to have any coments or adviser, speciallly the hard ones , as now i am working on and i can change or add anything
The only basic diference with other terracota pots is enamel the interior to avoid transpiration in the botton, under the water level hole

thanks in advance

[Ray]

As the inventor of the technique, let me throw out a couple of observations.

• I think your reservoir depth is too great. For a 14 or 18 cm tall pot, I usually make them no greater than 3 cm above the bottom. Granted, a plastic pot is much thinner than clay, so I’m sure that bottom reduces the depth a bit.
  
  When you plant in S/H, the roots must be above the reservoir level; your current proportions make that a bit difficult.
  
  
• You’re better placing two, 6mm holes as close together as possible, without them intersecting. That way, if a LECA pellet blocks one, it will prevent the other from becoming so.
  
  
• All those extra holes should be eliminated.
  
  In a semi-hydro pot, the wicking of the nutrient solution upward is opposed by evaporation starting at the top and moving downward. Ideally, you want the entire column of pellets to be moist. The extra holes accelerate the evaporation process, cancelling the wicking.
  
  
• The use of unglazed terra cotta will, indeed, lead to water passing through the pot wall and evaporating. That, coupled with evaporation from the contained LECA will lead to some significant cooling of the root zone. That will limit the orchids that will do well, unless you grow in a very warm, very humid environment. For example, phalaenopsis roots can die if kept wet and too cold.
  
  In an experiment using plastic pots (i.e., no cooling from the sidewalls), I saw 4F cooling at 74F & 35% RH.

[Orchidcork]

Thank you very much Ray for your opinion, regarding the holes in the tank, I think it's a good idea to put them together.

Then there are two points that I don't agree with
1.- You say that hydroponics works by evaporation, but I think that hydroponics works by the great capillarization of the LEKA.
The nutrients do not rise with the water when evaporating, as occurs with the salts, which remain in the containers when the water evaporates.
Not so with capillarization as we can see in cement houses where due to capillarization the salts rise and I think that's how the Semi-hydroponics works
In fact, for this very reason I think that putting the complete terracotta tube increases this capillarization even in the walls

2.- For this reason I think that my experiment of putting those extra holes in the rest of the tube, for the Cattleya pots should work, we'll see.

3.- AlsoAbout this matter of the 4 degrees of difference between plastic and terracotta, I would like to know more.

Regarding what you say about Phalaenopsis, this is not a problem that can occur in cold climates, with clay pots, since the cooling effect produced by evaporation is due to the heat absorbed to transform the liquid into gas, so in cold environments there is almost no evaporation.

This is why evaporative air conditioners work better in warm and dry environments, where evaporation does occur.

As for the 8 cm in the finished Catasetum pots, I made them at 8 cm because that is what a Catasetum grower asked me to do.

But the ones I am making now, the ones that are only in the photo, with the clay still wet and uncooked, in which I want to put Cattleyas, we are in agreement, because I have put the drainage holes much lower, if you look, the hole is at 5 cm, plus the thickness of the bottom and 1 cm left from the clay when it is completely dry, it will be at 3.5 cm.

Thanks again for your comments, I'm still in the seedling stage when it comes to orchids.

[Ray]

Originally Posted by Orchidcork

1.- You say that hydroponics works by evaporation, but I think that hydroponics works by the great capillarization of the LEKA.
The nutrients do not rise with the water when evaporating, as occurs with the salts, which remain in the containers when the water evaporates.
Not so with capillarization as we can see in cement houses where due to capillarization the salts rise and I think that's how the Semi-hydroponics works
In fact, for this very reason I think that putting the complete terracotta tube increases this capillarization even in the walls

2.- For this reason I think that my experiment of putting those extra holes in the rest of the tube, for the Cattleya pots should work, we'll see.

Apparently I was unclear.

Of course it works because the solution is wicked upward. My point was that evaporation works against that.

In any container, most of the evaporation is from the top surface. If the rate of wicking (a fixed parameter, based upon the specific material) is greater than the (variable) rate of evaporation, the LECA stays moist clear to the top. However, if the evaporation rate is greater than the wicking rate, the the liquid will have evaporated before it gets all the way up.

As the liquid evaporates, the dissolved solids are deposited on and in the LECA, ultimately leading to a level of being toxic. (Early on after the technique was introduced, several folks merely topped up the reservoir when they watered, rather than doing a top-down flush. Within 2-3 years, the LECA was so contaminated that their plants declined and died.)

Extra holes accelerates the evaporation process, exacerbating the issue.

One thing that had not occurred to me was that the pot walls will wick water upward as well, so maybe that compensates a bit. (In that case, I'd dip the green body in glaze to the depth of the reservoir, providing an external barrier and allowing the clay to absorb more.

I still think limiting the pot to two 6mm holes is better.

3.- AlsoAbout this matter of the 4 degrees of difference between plastic and terracotta, I would like to know more.

What I stated was that in the environment is used, wet LECA alone had enough evaporation that it cooled the medium by 4°F. My speculation is that, as the clay pot will also introduce surface evaporation, the cooling could be more severe.

Evaporation may be slower in cooler temperatures, but you cannot disregard it as a factor.

I grew all my phals in S/H in my warm, humid greenhouse when I lived up north. After moving south to a home with no greenhouse, they did great out on my deck in 90°+F/90%+ RH conditions, but when I brought them inside for the winter, the cooler (68°F) but drier (35%-45% RH) air resulted in enough cooling that I lost some phal roots - particularly with hot-growers like bellina, venosa, and the like.

Regarding what you say about Phalaenopsis, this is not a problem that can occur in cold climates, with clay pots, since the cooling effect produced by evaporation is due to the heat absorbed to transform the liquid into gas, so in cold environments there is almost no evaporation.

Untrue. Except at absolute zero (-273°C), ALL gases contain "heat". It may be less in cooler air than warmer, but it's not none, and the driving force to maximize entropy still causes water molecules to leave the liquid phase and disperse into the vapor phase, and that will absorb heat.

[Orchidcork]

Originally Posted by Ray

As a medium in traditional culture, I doubt there will be much issue with temperature. In S/H culture, I would guess there would be more of an issue.

My guess at the scenario: a little bit of evaporating water has a little bit of cooling effect. Once the water content of the medium decreases, the cooling effect does, as well.

In semi-hydroponics, the water content in the medium doesn't decrease, so the evaporative cooling effect continues, making the medium cooler. There is a moderating effect, of course, as the cooler temperature slows evaporation.

It is not unclear, it is just exaggerated in the physical or chemical consequences of using my design, as occurs in the consequences of evaporation in cold environments, when you say that what I say is false, and in this way you even go against what you say in another post,

Well, the rate of cooling by evaporation is proportional to the heat and therefore to evaporation. The higher the heat, the greater the evaporation and the greater the cooling, the lower the heat, the lower the evaporation and the rate of cooling due to evaporation practically disappears.

Anyway I agree what you say about evaporation, that is why I have shortened the height compared to the other pots, in this way we have the advantages of greater aeration in the roots and we continue to benefit from the effects of the capillarity of the leka

As for the faster saturation of salts in my design due to evaporation, I don't see it as dramatic, because as you say the walls of my system act as a buffer, it will simply be necessary to wash the leka as it already happens in the traditional semi-hydroponic system.

This occurs in all substrates, of any cultivation technique. Because we already know that alkalinity or acidification limits the assimilation of nutrients in plants and it occurs more in semi-hydroponics because many more salts accumulate as they do not leave the pot.

Therefore I think it would be interesting if you could give a leka cleaning protocol for semi-hydroponics in general.

I am usin another way of "semi-hidroponic" in my cattleyas pots, where you can remove the deposit so is much easier to clean.