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Old 08-31-2015, 01:48 PM #31
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Damn Waxy - I went so deep into the rabbit hole I forgot it was in your thread that I had first come across VPD. I've had been skipping right to the most recent post whenever I go to it...it's right there in your initial post. Thanks for putting that out there for my eyes to see. I think being aware of this whole VPD thing will prove to be very useful in the future.


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Old 10-27-2015, 05:25 PM #32
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VPD Guidelines

I'd follow the Tomato guidelines and follow-up on these studies if wanting more details, solid and relevant, indoors allows for probably slightly more deficeincies but when VPD is right, your RH will be surprisingly high indoors and in GH, always, for near all plant species baring cactai / succulent family & similar .....

"Growers should aim to have fairly low VPD, for example 0.3 kPa, when rooting cuttings in greenhouses. This will reduce the drying of young plants, thereby reducing the frequency of misting and watering required to keep plants hydrated. However, Michigan State University Extension recommends maintaining a greater VPD (greater than 0.5 kPa) in greenhouses while finishing plants, especially when there is a dense plant canopy. Plants will be able to transpire, cool themselves and be less stressed while the environment is less conducive to disease.

Greenhouse vegetable growers harvesting fruits should be aware that one study, “Vapor Pressure Deficit (VPD) Effects on the Physiology and Yield of Greenhouse Tomato,” reported that a VPD of 0.8 kPa during the day and night increased photosynthetic rates and tomato fruit yields compared to plants grown with a VPD of 0.5 kPa. Too dry of an environment can also cause problems. For example, another study, “High Vapor Pressure Deficit Influences Growth, Transpiration and Quality of Tomato Fruits,” showed that a very high VPD of 2.2 kPa could cause plant stress and fruit cracking in tomato.
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Old 10-27-2015, 06:23 PM #33
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Hey Ko, hope your adventure is going well.

I noticed I did not know what kPa was and did some research I thought I'd share with you guys..

https://cronklab.wikidot.com/calculat...essure-deficit

"

For example take 80% RH at 25 C. From the list above, SVP = 3167 Pa

100-RH = 20
20/100 = 0.2
0.2 * 3167 = 633.4 pascals (Pa)

Note: for convenience VPD may be given in kilopascals (kPa). For this example 0.6334 kPa."

....


In regards to Led05, do you have any links to these study's from MSU? I am very curious as to what they found...thanks
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Old 10-27-2015, 08:13 PM #34
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i was just gonna bump this thread! how's everyone's projects going?

i just split my flower room into flip flops thanks to this thread and WT's thread.
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Old 10-27-2015, 11:05 PM #35
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Thumbs up

https://www.growell.co.uk/blog/2014/0...essure-deficit

had to look it up, VPD = vapour-pressure-deficit.


When the air is dry, the plants lose more moisture through their leaves and buds, so they have to be watered more.

I think.
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Old 10-28-2015, 05:11 AM #36
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Waxy...

https://msue.anr.msu.edu/news/why_sho..._deficit_and_n

Decent links in there, I shoot for .75-1.2kpa, not running more than 75%RH in winte, inside
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Old 10-28-2015, 05:38 AM #37
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https://www.google.com/url?q=https://wsp.arizona.edu/sites/wsp.arizona.edu/files/uawate

Here's a good one too...
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Old 10-28-2015, 02:43 PM #38
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Sorry about that link, just Google "VPD Tomatoes Arizona", Dry climates like AZ naturally have significant VPD issues so a good place to start, homes, buildings in general are arid due to HVAC both winter & summer & natural effects of having a room(s) much warmer than surrounding creates even greater VPD issues unless you want mold to potentially seep into the rest of your home I'd target Kpa of .75-1.25 which are reasonable but in 80's this still equates to surprisingly high RH numbers... For years what I thought was mag, molybdenum, iron etc deficiency were clearly VPD issues, LED added to this confusion naturally BC the underlying opinion is they cause excessive cal/mag usage, my guess unless you're living in the SE USA, you're feeling some level of VPD, especially indoors. To previous poster about ideal levels indoors vs. A GH, who cares, both are controlled environment, same effect on plants but structures do function differently, this doesn't change the VPD / Kpa required numbers..... Anyone ever grow orchids, inside ....?
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Old 10-28-2015, 07:01 PM #39
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good links thanks led05
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Old 10-28-2015, 07:28 PM #40
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There needs to be a VPD sticky... why no this thread as it expands?
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