cavadge

Hey all,

I've only been growing indoors a short time, am not a meteroligist, botanist, biologist, or scientist, have no expensive equipment or tons of statistical data, but I do track grow data daily and am a lifelong observer of things. I record PH and TDS daily, min, max and time stamped room temperature and humidity, from four different areas, including grows, moms and clones. I keep a clipboard at each area and record all the data daily. I use a high quality thermometer/hygrometer in each area to ensure accuracy and consistency. Milwaukee/Martini instruments are used and calibrated weekly. Lighting, ventilation and temps are all dialled in. No plant diseases or other grow issues.

Again, not an expert grower, and all my gear is hydro. However, I've begun to learn the art of nutrients, and have gotten a pretty good handle on what the plants need, and when. And while I've seen my PH drop and TDS climb before, and read many threads on the subject, up to now I just assumed I wasn't feeding the plants properly.

Getting to the point...

We've had a lot of rainy periods since August, a noreaster a week or so ago that provided five days of nonstop rain, and more recently another weather front that moved through here over the weekend. And in the last 12 weeks or so I've begun noticing a pattern.

While I've been able to establish a good level of nutrients, and plants are thriving, I was bothered by inexplicable changes in PH and TDS. Why was it that over a period of time PH slowly crept up, while TDS slowly dropped (ie feeding well), and then suddenly one day everything went the other way? I kept asking myself what would account for that.

The key question - so what has changed? The only thing that came to mind right away was - the weather. So I began keeping track of weather fronts. And each time a low pressure system moved into the area, I've noted a PH drop and TDS rise. And I see this continue until once again a high pressure system moves in.

And I noted it again this weekend. A system moved in on Friday. Rained Friday night into Saturday night. Readings Friday evening - PH down, TDS up, all around. Saturday - PH down some more, TDS up some more. Sunday morning, high pressure system moves in. Readings Sunday evening - PH coming back up, TDS going back down. On all the systems, consistently. I'm thinking I'm going to add a barometer to the grow room and start recording that daily as well, to establish some corresponding data.

Am seeing this now over a three month period. Haven't researched this in any detail as yet, but thought to pass this on for discussion. Has anyone else noted anything like this?

tripps

Very interesting, I will try to see if I notice any correlation.

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g1ithc

is relative humidity in the grow environment controlled?

that's pretty interesting!

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GreenDragon2k

I wonder if its a change in the uptake of nutrients in the plants or if its a chemical change in the water due to a pressure shift? Very interesting findings. I'll take note myself.

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sillysister

That is indeed interesting! My first thought is, of course and why not? I bake bread. You can use the same ingredients, same technique, and if using a machine, the same machine. But loaves will turn out different due to climactic changes. Some will be very light & airy while others can fail completely and be as hard as bricks. Others will fall in variance in between those two extremes. Sometimes you'll have to add more of this or less of that to compensate for the barometer. So it makes total sense to me that the same could be true of growing cannabis in artificial conditions that could be subject to fluctuations in the weather.

Great observations! Thanks for passing them on!!!

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GreenDragon2k

This would actually make sense and is a great question, if the humidity went up, the plants' transpiration would go down. Reducing nutrient uptake and causing the TDS to be too high, therefore making it climb and causing the pH fall exactly as described.

If the RH is controlled however, this would seem to mean that the barometric pressure caused a reduction in nutrient uptake on its own. Does barometric pressure affect osmosis? It would make sense that it would.

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countyspud

Osmotic pressure is affected by barometric pressure in an aqueous solution.
Also as plants get older the duration of the affect of barometric pressure increases. Methinks this is where the answer lies. the size of your res also determines how much of an affect it has.

There is an equation for this but I can't find it on google.

I did find a book:
The osmotic pressure of aqueous solutions: report on investigations made in ...

By Harmon Northrop Morse

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cavadge

Re: grow room humidity - I've been able to hold it between 47% and 57%. Two dehumidifiers keep it pretty stable.

Going to check that link countyspud. Thanks for that.

I became aware of changes in how I felt with changes in the weather quite some time ago, and have been an observer of this since, in myself and in others. When the barometer drops, I've noted people and animals get lethargic, irritable, tired, and have trouble focusing and getting their work done. My dog usually just sleeps that time away, up to 18 or 20 hours in a day. Some people (me for one) get migraines and sinus headaches. The last three hurricanes or remnants passing through here made me feel ill, as if I had the flu. I experienced extreme lethargy, fatigue, sinus headaches, and an inability to think clearly or focus.

As a rule, once the low pressure gets pushed out by a high pressure front, I feel re-energized, and I see the same in my dog and the wildlife around me. If people and animals are affected by low barometric pressure, then it stands to reason all other forms of organic life, including plants, are impacted in some manner.

rollingrufus

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