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Mastering Humidity and VPD · Hydroponics Daily

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  Hi, welcome back to Hydroponics Daily. Today we're talking humidity.
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  So we control the humidity in a hydroponic grow room or a greenhouse for three main reasons.
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  The first, when you are propagating, is to prevent cuttings or clones from dehydrating.
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  So you whack the humidity up to nearly 100% and this prevents the cuttings from dehydrating.
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  They've got no roots, so you want them to limit the amount of water they transpire.
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  And until they get some roots so you're not looking for
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  any photosynthesis to be occurring you don't need
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  transpiration to occur you don't need movement
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  you're not worried about calcium deficiencies and and things
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  like that so you're just keeping them as hydrated as
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  possible by keeping the humidity high saw a great instagram
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  post today from a company saying plants take
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  their the water in through their roots and through their leaves
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  that's not true they don't take watering through their leaves they
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  do lose water through the leaves so having
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  a high humidity prevents that the second reason we
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  want to control humidity is to prevent or
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  to control or limit pests and diseases so particularly things like powdery mildew
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  that thrive in really high humidities you don't want once your plants have propagated
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  and have rooted you then want to take the humidity down to at least 70% for most crops.
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  And then sometimes, even when you get into flowering, you might want to take
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  that down to 40% relative humidity.
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  So 100% being the most, the amount of water that the air can hold,
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  the most amount of water it can hold at that temperature.
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  And obviously, the higher the temperature, the more water it can hold.
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  So hence, relative humidity.
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  So in colder temperatures, the amount of water it can
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  hold is very little as your grow room gets
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  warm then you have to have a humidifier to
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  maintain the same amount of humidity because what was the
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  amount of water per cubic meter for it
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  at five degrees celsius and for 100 humidity would
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  be not even 20 at 35 degrees
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  celsius so the warmer it gets the more you're
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  going to need a humidifier unless you're living in a
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  very humid environment like florida for example so things
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  like as we said we want to reduce the humidity to prevent things like
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  mildews and then you want to then at
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  the lower end you want to prevent things your plants just crisping up and drying
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  out too quickly so you get you get the leaves dying off the tips dying off if
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  the humidity is far too low so that would be the third reason you control humidity
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  is to prevent them just drying out too much and losing too much water.
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  However, that tends to be less, unless it's really hot, that's less of an issue.
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  Remember, you need air movement around your grow room or around your grow,
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  your greenhouse, because around the heater, if you've got a heater in there or a light,
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  that will increase the temperature rapidly and you'll have much lower humidity around those areas.
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  So make sure you've got good airflow so you've got a more uniform humidity.
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  You measure humidity with a hygrometer and
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  often confused with hydrometer it's not a hydrometer hydrometers
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  are used for measuring the density of liquids i believe a hygrometer
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  measures the humidity and so we always measure
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  it in relative humidity so you'll have a normally have a device that
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  measures temperature and humidity it might
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  it might have a data logger that measures both or
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  you might just have a max and a min if you have a data logger
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  you can actually measure something called vapor pressure difference or
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  vpd and that's really important because
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  vapor pressure difference is the difference between the current
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  amount of water in the air and that of saturated air that's termed vpd and that's
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  very important for plants and it's linked to plant health tremendously and you
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  will find that commercial controllers will allow you to automate things like
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  your humidifiers dehumidifiers.
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  Heaters ventilations fans and link
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  that to a certain vpd now you
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  can get vpd charts that tell
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  you for a certain temperature and a certain humidity what your vpd
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  is and you'll have like a green zone which is
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  ideal for your plant you'll have a yellow
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  zone an orange zone and a red zone where you want to stay as far
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  close to the green as possible and you can do that manually and adjust manually
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  depending on the current temperature you can increase your humidity up and down
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  to make sure you've got the right VPD for your crop and it will change somewhat
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  between certain crops as I say I've only grown one crop that actually ever needed
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  really really high humidity.
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  I can't tell you which one it is because that fact is actually top secret,
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  but most ones you want, even if it thrives under high humidity,
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  you don't want it to go really high because you're going to be stimulating those
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  mildews and rusts and other foliar diseases.
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  I'm not sure of any pests that like either high or low humidity.
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  I would imagine a lot of sap sucking insects like the humidity to be quite low
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  because then you're stimulating sap movement.
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  And so the more sap, the more the sap they can suck and things
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  like that so probably insects like low humidity and then
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  spider mites they wouldn't want it really high humidity because then
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  droplets would form on their webs and you'd be able to notice them
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  too too early so yeah i would have
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  thought there's some interaction there with pests and humidity another way
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  of looking at vpd is just the amount
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  of drying power the air has on your
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  on your plant that's one way of looking
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  at it i think a number of the the new
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  controllers sort of ai controllers and things like this ai.
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  Powered controllers will increasingly use vpd
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  to either guide guide you or
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  just control the controllers in your grow room if you've
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  not seen a vpd chart i highly recommend downloading one
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  and printing it off sticking it up in your grow room
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  it's probably the one resource that you should have printed printed off
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  to refer to if you've got a hygrometer and.
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  A thermometer in your grow room so you can make sure that you
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  are in the green zone for your crop this is
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  certainly the sort of next step after sort
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  of making sure your plants are in the right temperature and humidity for
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  sort of range obviously you know you can
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  say like your plant might need 15 to 25 degrees
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  celsius and humidity to 40 to 60
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  degrees 40 to 60 percent however the
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  extremes of that would not be ideal so
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  a humidity of 40 at
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  25 is completely different environment to
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  15 at 60 and one
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  plant will thrive and one plant will not thrive in that so vpd really
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  dials it in a lot more and allows you
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  as the temperatures become more extreme so you've
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  lost control of temperature and you just cannot control temperature or you
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  cannot control humidity one or the other then you can still
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  make sure that the environment is correct for your plant growth
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  and they won't suffer so that's the first thing you
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  can do that's the next step as it were in becoming a bit
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  more of a professional grower and then you can
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  look at controllers that use vpd to automatically control the equipment in your.
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  Grow room and then a step up from that is controllers that would look at leaf
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  temperature and leaf temperature is more indicative of how the plants respond
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  to VPD and rather than air temperature.
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  The stomata are closed then they need different environment
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  conditions and so the stomata might be closed because the
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  water's deficit you might be using running a water deficit
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  treatment in the soil or the growing media or
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  there might be the light conditions and things like that
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  so using something that measures leaf temperature
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  either a thermocouple or a thermal imaging camera that's
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  a step beyond i'm not sure of any controllers that use thermal imaging
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  cameras to actually automate you can
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  certainly buy cheap thermal imaging cameras now that
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  go onto your phone and things like this or incorporated into
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  a phone for a couple of hundred dollars and things like
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  this so there used to be hundreds of thousands of pounds back when
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  i was working at lancaster university so there
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  are ways you can increase this is probably a good way where
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  you can step up and improve your grow grow after
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  grow by looking at vpd and dialing everything in things.
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  Like when you're growing lettuce often let's i always say about lettuce it
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  either just doesn't grow and just stays in stasis or
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  it grows like mad and you can never tell why it
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  is and i always think it's probably related to
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  vpd because you can give it the right what you
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  think are the right conditions yeah humidity looks great the the
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  temperature looks great but are you actually dialing in
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  the vpd and if you dialed in the vpd i think lettuce is
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  like lettuce just really go hell for
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  leather and just you can't stop them growing when you
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  get things right so that's something to consider today's hydroponics
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  daily is a bit more on humidity and certainly a bit more on vpd which you'll
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  hear a lot of grow shops talk about they're fairly well knowledgeable when it
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  comes to vpd certainly a lot of the control people the controller salesmen that
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  go into the grow shops they know what they're talking about it's taught by a
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  lot of you know on a lot of botany and.
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  Horticultural courses now it's not taught on many agricultural
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  courses because you can't control humidity and temperature
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  outdoors that's been hydroponics daily for today thank you
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  very much for listening if you are able to give us a review on either spotify
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  or apple i'd be tremendously happy really want to see us shoot up those charts
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  and overtake things like the rhs and gardens world magazine stuff like that
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  until tomorrow thank you very much i'll have another banger of an episode for you. Ta-ra!