LordDankinstien
- 517
- 28
Ok im not taking credit for this post at all!!! I found it somewhere else and the information is very usefull or at leaste it clears up some questions you might have. Im no expert at this so I wont be answering questions im just post this info as some brain food. :bong2:
relative humidity is an expression of the actual water vapor pressure, expressed as a percentage of the maximum water vapor pressure possible under certain air+atmospheric pressure conditions.
@ room temp (~60*f), 100% humidity exerts a vapor pressure of 24 torr (~4.65 pound-force per sq "[24*{19.337*10^-3}]=4.65 psi pound-force). >24 torr of vapor pressure exerted on leaves, and leaves sense a vapor pressure deficit.
leaves stomata opening/closing influenced by difference between internal/external vapor pressure. opening/closing of stomata regulates gas exchange+transpiration, which in turn regulates growth/fruiting.
vapor pressure deficit is a lack of water pressure upon plant. this would be a low rh. it is indirect measure of water loss from plant. as plant attemps to balance internal/external vapor pressures, they draw up more water from roots and transpire it into the atmosphere. hence the de-humidifiers used in gardens.
air movement over plant+high temps+low rh reduce plants available water for sugar production. the roots uptake much more water during low rh. but all inter-related to ambient temp(avg. surrounding air temp), actual leaf temp, and root temp.
a 3'x3' plant can transpire a gal. during high vpd (low rh), or a cup during low vpd (high rh). vpd/rh measurements must take into account air temps.
generally, keeping rh as high as possible (~55-75%) keeps the plant in a comfort zone to its genetic desires. lowering rh provides a method of tailoring nute formulas, pushing parameters, etc - as they will be taking up much more water. keep in mind that the water uptake during low rh is mostly just that - water. keeping nute ppm/ec in balance w/ ph is good idea.
prevention of mold/diseases/condensation is the reason for decreasing rh, but it can be higher w/ air exchange/movement w/ tempered evaporation (air movement over/around plants). also, growth slows during high rh, but in fruiting, slow growth is not an issue, fruit production is. lower rh also increases translocation of calcium (why gardeners use calcium additives during fruiting - it is sent to every part of plant during increased water uptake via roots).
not having problems because the plants' comfort zone is pretty broad w/ comparable temps+air movement - just like there's a 'domain+range', so to speak, in nute levels, etc.
note: in general...
lower rh(high vpd)=increased transpiration, translocation, water uptake, greater calcium absorption/transport.
higher rh(low vpd)=slower transpiration, translocation, water uptake, slower evaporation, increased growth.
rh does not need to be >50%, it needs to be tailored to specific environment, w/ specific temps/air circ variables accounted for. can manipulate growth/water uptake from that comfort zone point (~45-65%, again, depending on gardens other inputs).
water uptake from roots+stomata opening/closing+transpiration are inversely related, but non-linear.
lowest water uptake prior to lights on. stomata closed @ night, partially closed @ mid-day (hottest) so as not to evaporate too much water.
Below is another post from the same person
stomata opening/closing is influenced by rh(vpd), temp(diff), light(spectrum(s)), hormones, etc. not isolated to rh influence. lot of science in this. discoveries in plant science/ag eng still continuing. basically, no variable can be read in isolation in garden environ.
most important time to influence/test/experiment on plants w/ different rh/higher night temps/etc. seems to be ~before sunrise/sunset, when the internal clock is most sensitive.
Hope you guys enjoy this I know it answered alot of questions I had.
relative humidity is an expression of the actual water vapor pressure, expressed as a percentage of the maximum water vapor pressure possible under certain air+atmospheric pressure conditions.
@ room temp (~60*f), 100% humidity exerts a vapor pressure of 24 torr (~4.65 pound-force per sq "[24*{19.337*10^-3}]=4.65 psi pound-force). >24 torr of vapor pressure exerted on leaves, and leaves sense a vapor pressure deficit.
leaves stomata opening/closing influenced by difference between internal/external vapor pressure. opening/closing of stomata regulates gas exchange+transpiration, which in turn regulates growth/fruiting.
vapor pressure deficit is a lack of water pressure upon plant. this would be a low rh. it is indirect measure of water loss from plant. as plant attemps to balance internal/external vapor pressures, they draw up more water from roots and transpire it into the atmosphere. hence the de-humidifiers used in gardens.
air movement over plant+high temps+low rh reduce plants available water for sugar production. the roots uptake much more water during low rh. but all inter-related to ambient temp(avg. surrounding air temp), actual leaf temp, and root temp.
a 3'x3' plant can transpire a gal. during high vpd (low rh), or a cup during low vpd (high rh). vpd/rh measurements must take into account air temps.
generally, keeping rh as high as possible (~55-75%) keeps the plant in a comfort zone to its genetic desires. lowering rh provides a method of tailoring nute formulas, pushing parameters, etc - as they will be taking up much more water. keep in mind that the water uptake during low rh is mostly just that - water. keeping nute ppm/ec in balance w/ ph is good idea.
prevention of mold/diseases/condensation is the reason for decreasing rh, but it can be higher w/ air exchange/movement w/ tempered evaporation (air movement over/around plants). also, growth slows during high rh, but in fruiting, slow growth is not an issue, fruit production is. lower rh also increases translocation of calcium (why gardeners use calcium additives during fruiting - it is sent to every part of plant during increased water uptake via roots).
not having problems because the plants' comfort zone is pretty broad w/ comparable temps+air movement - just like there's a 'domain+range', so to speak, in nute levels, etc.
note: in general...
lower rh(high vpd)=increased transpiration, translocation, water uptake, greater calcium absorption/transport.
higher rh(low vpd)=slower transpiration, translocation, water uptake, slower evaporation, increased growth.
rh does not need to be >50%, it needs to be tailored to specific environment, w/ specific temps/air circ variables accounted for. can manipulate growth/water uptake from that comfort zone point (~45-65%, again, depending on gardens other inputs).
water uptake from roots+stomata opening/closing+transpiration are inversely related, but non-linear.
lowest water uptake prior to lights on. stomata closed @ night, partially closed @ mid-day (hottest) so as not to evaporate too much water.
Below is another post from the same person
stomata opening/closing is influenced by rh(vpd), temp(diff), light(spectrum(s)), hormones, etc. not isolated to rh influence. lot of science in this. discoveries in plant science/ag eng still continuing. basically, no variable can be read in isolation in garden environ.
most important time to influence/test/experiment on plants w/ different rh/higher night temps/etc. seems to be ~before sunrise/sunset, when the internal clock is most sensitive.
Hope you guys enjoy this I know it answered alot of questions I had.
