Mosses, weeds and ferns... Bad or good?

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Everybody is expressing concerns about air movement in the pots when ferns have sprouted. You do realize the largest source of air is when you water? When you pour tons of water onto your pots the action of the water rushing draws huge volumes of air into the pot at the same time. You have no problem with air in the pot if this is how it works when you water but if the water puddles at the top of the pot as soon as you add water...you have a problem. You can have either condition with or without the cute ferns. I'm sure the lady with the dendro and the fern had this issue and didn't realize it.
 
In time bryophytes can create quite a thick carpet over the top of the pot which can inhibit watering, and speed up break down of organic substances in the pot, as well as sponge up a lot of moisture, which isn't great for epiphytes.
 
SlipperKing said:
QUOTE] You do realize the largest source of air is when you water?
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Actually, diffusion is the main way air gets into media. The larger pores in the medium are in contact with the atmosphere and down to the roots through a maze of pores. As roots and microbes use oxygen, so more is then diffused in. The rate depends entirely on size and number of pores in contact with the atmosphere. Watering has only a minor overall effect on air availability. Consider a tree in the desert that hasn't recieved rain for 10 years.
 
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I think there is a difference between a parvi in my greenhouse getting watered every three days and a tree in the desert getting rained on every 5 years, water draining through a pot will certainly pull air along with it as well as behind it. That diffusion occures along concentration gradients is also accepted.
 
Trithor said:
I think there is a difference between a parvi in my greenhouse getting watered every three days and a tree in the desert getting rained on every 5 years, water draining through a pot will certainly pull air along with it as well as behind it. That diffusion occures along concentration gradients is also accepted.
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No difference. The tree will need just as much air as the paph (more or less) If a plant in a pot had to rely on air getting sucked in with watering it would suffocate. The amount of oxygen held in the pores would surley get used in a matter of several hours. Especially by a plant with many roots. Not to mention the billions of aerobic microflora.
 
This discussion on the efficiency of the oxygen penetration in the substrate remembers me the following story. A few years ago I visited a producer of Phalaenopsis here in Belgium. He said to me that one of its two tanks for rainwater storage gave a better growth of its plants than the second tank. He explain me that this is just because he had installed an air blower to inject air in the first tank.
 
I think the amount of gas diffusion in a pot is not influenced greatly by the amount of moss cover or fern root density as a mechanical function of material density (its just not that well sealed).

But you can have CO2 buildup based on plant and bacterial respiration that could go up and down considerably during light/dark phase based on the amount of "biology" going on and the amount of water in the pot.

This would probably be expressed as fluctuations in pH rather than dissolved oxygen (which would probably stay close to saturation unless the mix was really broken down, dripping in water, and sealed top and bottom).

Humans use a lot more oxygen than plants, and I bet you can still breath through a handful of moss. A dust mask is less porous to gasses than a layer of moss, and people don't suffocate in dust masks.


A more useful analogy is sticking a bunch of people into a room. The amount of leaks seems to prevent suffocation from lack of oxygen, but the CO2 concentrations increase enough to measure pH drop in water vapor (including in the lungs).

Water loves to suck up CO2 but not so good at O2. As CO2 goes into unbuffered water it converts to carbolic (carbonic?) acid to lower pH.


At what point is this bad for plants or humans????
 
Rick, do this experiment:

Take a small glass with about 2 oz of distilled water, out of a just-opened bottle. Stick a pH meter in it and leave it on. The initial reading should be 6.9-7.1.

Now take a drinking straw, place it in the water and exhale through it. Watch the pH go down. After about 5 minutes of this, it should be down near 6.5. But just like raising pH with aragonite sand, this isn't a linear relationship. Airborne CO2 alone won't take the pH down by more than 1 full point.

I did a related experiment a while ago when I wanted to measure the pH of my mineral composite material, both untreated and treated with lithium silicate. The test consisted of pouring small puddles of water on the surfaces and taking pH readings with strips (0.5 accuracy).

Untreated started at a pH of 11.0 and after about 4 hours it reached 10.0. After 8 hours, it still read 10.0. Treated started at 9.0 and levelled out at 8.0. The most surprising finding was that after 8 hours, I still had puddles of water on flat surfaces.
 
Actually we do this experiment fairly frequently. Human exhalation doesn't have that much CO2.

We use bottled CO2 gas, and use a CO2 monitor to control a solenoid valve. Depending on the buffering content of the water to start with, we can get the pH to drop to about 5.0 in standing water placed in the room. This system is actually made for GH use, but we use it in the tox lab to stabilize the pH of water samples. The toxicity of ammonia and many metals is pH dependent. So as gas balance changes in buffered water samples, the pH will generally rise over the coarse of the test duration.

But I would agree you can't get the pH to drop below ~4.5 no matter how pure and how much CO2 you pump into a room (or bottle of water). Check the pH of a freshly opened bottle of Perrier water, and then aerate it for a few hours and check again.

Not sure if anyone is using the CO2 injection systems for home aquarium systems anymore. But these were popular for aquariums specializing in live plants. These used pH controllers to regulate the CO2 injection. Granted you didn't want to drop the pH lower than 6-6.5 if there were fish in the tank.
 

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