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Thread: will LOW humidity hurt a plant?

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    Sjapp is offline Registered+
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    will LOW humidity hurt a plant?

    If your humidity is around 20% or lower can it be bad for the plant? If it is I don't understand why it would be bad for the plant because the leaves don't absorb water do they?
    Last edited by Sjapp; Feb-18-2008 at 13:51.

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    Quote Originally Posted by Sjapp View Post
    If your humidity is around 20% or lower can it be bad for the plant? If it is I don't understand why it would be bad for the plant because the leaves don't absorb water do they?
    From what I've read - and this could be biased information, so take it with a grain of salt - but humidity levels lower than 30% prevent the stomata on the leaves from opening fully (or at all) and reduce the transfer of C02 and other gases to the cells of the plant. Slow growth and symptoms similar to nutrient burn can result, but aren't always typical. If most other conditions are optimal, excessively low humidity may not pose as much of a problem. It certainly beats excessively high humidity any day.
    Quote Originally Posted by stinkyattic View Post
    Switch to 24/0 light schedule and don't worry... about a thing... every little thing... gonna be all right.
    Quote Originally Posted by Rusty Trichome View Post
    It can be a fine balance between "ok...I need to water later today" and "shit...I should have watered yesterday."
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    Yes, water and nutes are absorbed thru the leaves.

    I live in the desert. During the summer the temps get to the 120's, and humidity get's up into the teens . You mentioned nothing about the heat, but excessive heat combined with low humidity, and the plant can struggle to keep upper zones hydrated.

    I veg indoors, and mist the plants once daily, as they much prefer the higher humidity. But I flower in an outdoor shed, where the A/C keeps the temps around 90ish and the plants have little to no problems adjusting. Keep an eye on them daily, especially when they start filling-out. The larger the plant, the more moisture they lose thru the leaves. (transpiration)
    Oversize pots will hold moisture a bit longer, but don't keep the soil wet all the time, will cause root-rot.
    It can be a fine balance between "ok...I need to water later today" and "shit...I should have watered yesterday."
    Last edited by Rusty Trichome; Feb-18-2008 at 14:46.

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    Quote Originally Posted by Mr. Clandestine View Post
    From what I've read - and this could be biased information, so take it with a grain of salt - but humidity levels lower than 30% prevent the stomata on the leaves from opening fully (or at all) and reduce the transfer of C02 and other gases to the cells of the plant. Slow growth and symptoms similar to nutrient burn can result, but aren't always typical. If most other conditions are optimal, excessively low humidity may not pose as much of a problem. It certainly beats excessively high humidity any day.
    ha youre so humble, you sound like you know exactly what your talking about. so should i mist the plants or get a humidifier?

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    Quote Originally Posted by Sjapp View Post
    so should i mist the plants or get a humidifier?
    I'm lucky enough not to suffer from extremes in humidity, but if I were needing to raise it just enough to keep the plants happy, I'd probably spray them with a fine mist like Rusty suggested. There's less chance of over-saturating the air and not noticing it. I wouldn't, however, do any spraying during the last month of flowering. Even though it's generally suggested that higher humidity is a good thing in flowering, I'd rather lessen the risk of mold. But that's just me. If you happen to go the route of a humidifier, it would probably be a good idea to use distilled water... especially if you've got noticeably hard water at your house. Take care.
    Quote Originally Posted by stinkyattic View Post
    Switch to 24/0 light schedule and don't worry... about a thing... every little thing... gonna be all right.
    Quote Originally Posted by Rusty Trichome View Post
    It can be a fine balance between "ok...I need to water later today" and "shit...I should have watered yesterday."
    Plant problems? Fill out the Troubleshooting Form BEFORE asking how you should fix it!

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    colorado water is pretty damn good. maybe im turning a blind eye to it, but i don't think it needs to be distilled. ill mist for now, until i can get a humidifier.

    thanks

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    Rusty, is it difficult for you to keep your temps down for your indoor grows in the summers with that kind of heat?

    And regarding the outdoor, the plants do not mind growing in 90 degree heat? Any strain?

    This would be great news for me, as I cannot keep temps in my grow cab under 85, as I can't seem to get the ambient temps under 75. I was dissapointed because High Times and many things I have read on these boards say growth virtually stops at 90.

    peace
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    Quote Originally Posted by melodious fellow View Post

    This would be great news for me, as I cannot keep temps in my grow cab under 85

    peace
    you should try and get more exhaust. if you have a greater exhaust than intake it creates a low pressure vacuum effect in the room or box which causes cooling. its how all cooling systems work, be it your fridge or your ac

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    Nobody has said it solely/specifically but I thought that the humidity effects plants a bit like heat does us.

    I thought the humidity specifically changed the rate of transpiration.

    It also effects the amount of fungus that can viably grow.

    Hope these simple pointers help,

    Peace Out + GL,
    Denial

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    Quote Originally Posted by melodious fellow View Post
    Rusty, is it difficult for you to keep your temps down for your indoor grows in the summers with that kind of heat?
    Yes. But alas, I have no choice. Wifes friends (the church ladies) come over all the time, so indoor flower is out of the question.

    Quote Originally Posted by melodious fellow View Post
    And regarding the outdoor, the plants do not mind growing in 90 degree heat? Any strain?
    During the summer, I do have to stagger the 400w HPS' (12 to 14" or so from tops ) so only one is on at a time. I have it circuted to work like a light mover, light on the left is on for 6 hours, then just before it turns off, the light on the right comes on for 6 hours.
    It's usually around 110f outside, and the flower room is ok till that point. Once it get's up to the occational 120f, I raise the lights.
    130's outside, and I turn off the lights. Helps that I'm disabled, and am home most of the time.

    I also try to plan it so my Swazi Skunk (sativa) is the strain in line for the summer temps, but can't think of a strain I haven't finished in the heat, weather it's sativa, indica or hybrid.
    Instead of my usual 3 gallon pots, I flower in 5 gallon pots. Holds moisture a bit longer. Daily waterings up to around 3/4 gal per day per pot. Flushing the ladies is staggered over a week, too. Otherwise humidity skyrockets uncontrollably.
    Occational foliar for deficiencies, but keep it to a minimum, and only on the underbranches.

    I put an a/c unit in there, and it blows directly over the tops of the plants, and use a 12" fan blowing the cooler air up into the plants. I also have one of those breaker access panels (12" x 12") that is installed tword the top of my 9' tall room. I open it up, and have a dedicated exhaust fan blowing hot air out at all times. The intake is from the a/c.

    Quote Originally Posted by melodious fellow View Post
    This would be great news for me, as I cannot keep temps in my grow cab under 85, as I can't seem to get the ambient temps under 75. I was disappointed because High Times and many things I have read on these boards say growth virtually stops at 90. peace
    Alls I can say...it's a dry heat, and I strive to keep it dry. The first year, I misted heavy, and often, thinking they would like it. Burned the tops, and developed mold.
    Is it optimal...? No, but it most definatelly works. It can take an extra week or two to finish, but compared to my other options, I'll take it.
    Also, active trichome production starts a week or two later than usual, but come finish, they're just fine.

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    Quote Originally Posted by Sjapp View Post
    you should try and get more exhaust. if you have a greater exhaust than intake it creates a low pressure vacuum effect in the room or box which causes cooling. its how all cooling systems work, be it your fridge or your ac
    Thanks for all the feedback Rusty. You are a pal, bro.

    Regarding intake vs exhaust, I have heard, and I quote "nature abhors a vacuum." Now, if I can only remember the source and the respective credibility. I know theres a name the APA (psych association) has for that.... but as a stoner, I cannot recall that either

    I have also read that intake fans should be faster than exhausts so that air has time to circulate the cab before leaving.

    Not shore which is correct here, but I really appreciate the comments nonetheless.

    Maybe Stinky will drop by here.
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    Quote Originally Posted by melodious fellow View Post
    Thanks for all the feedback Rusty. You are a pal, bro.
    No problem, bro. Just payin' it forward.

    Quote Originally Posted by melodious fellow View Post
    Regarding intake vs exhaust, I have heard, and I quote "nature abhors a vacuum." Now, if I can only remember the source and the respective credibility. I know theres a name the APA (psych association) has for that.... but as a stoner, I cannot recall that either
    Was it "Witches ride brooms, because nature abhors a vaccuum", or "Everything sucks, Nothing else matters"...?

    Quote Originally Posted by melodious fellow View Post
    I have also read that intake fans should be faster than exhausts so that air has time to circulate the cab before leaving.
    Personally, due to my heat concerns, I'd trather have two exhaust fans at the top of my closet or shed, and an intake port (not fan) down low. The suction caused by the exhaust fans will bring in enough fresh air to keep the ladies happy.
    During the winter, I use one exhaust fan, and one circulation fan, but during summer I also use the a/c. so I guess technically it's an unintended intake fan.
    For me it's better to exhaust the hot air before it gets all mixed around the closet.
    Am I right? Shit...I don't know, but it kinda makes sence to me, lol.


    Quote Originally Posted by melodious fellow View Post
    Maybe Stinky will drop by here.
    Likely she will be.
    Last edited by Rusty Trichome; Feb-20-2008 at 08:28.

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    Unless your intake and exhaust fan are perfectly matched, just run an exhaust. Two mismatched fans will actually inhibit air flow and waste electricity.
    Your exhaust fan should PULL rather than push air. The duct for the exhaust fan should be high in the room, preferably attached to an air-cooled hood unless you run lights on a separate exhaust loop. A passive intake should be LOW in the room.

    High temps + low humidity + intense light are dangerous to a plant.

    Light:
    The plant transpires and photosynthesizes rapidly in intense light conditions, quickly using up water to form simple sugar by photosynthesis (sugar is a hydrocarbon; water contains a pair of H+ ions. The plant gets the carbon most efficiently from CO2 in the atmosphere).

    Temperature:
    The plant also cools itself by allowing moisture to evaporate off leaf surfaces.

    Humidity:
    The plant regulates its water loss and intakes atmospheric gases through the stomata, which are small openings concentrated on the undersides of the leaves. When the plant is trying to conserve water, and closes the stomata, it cannot breathe, and its metabolic systems start to shut down.

    What this all means is that when you are running BRIGHT and WARM, you must also add MOISTURE to keep the stomata open, and at temperatures above about 85 degrees, CO2 to ensure that CO2 is not the limiting factor in the plant's metabolism.

    When your conditions are COLD, and the plant is transpiring slowly, avoid overwatering, as moisture use/loss slows, and if you want to keep your plants fairly healthy even in low temps, you may want to decrease light intensity as well, because even though they may be able to photosynthesize under bright light, the chemical reactions that take place within the plant happen much more slowly. Below 65 degrees or so the plants become nearly dormant, and may be held in that state only under correct conditions.

    It's all connected. Hope that sorta helps.

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    Well, not to cause any rift, I'd defer to Stinky's knowledge.

    Do I recommend this to those with better finances, that can afford the equipment to coddle their ladies? No...but I am saying you can still make it work with a bit of extra effort. I do stand by my post.

    I've been forced to do what I do by necessity, and have found that, thru trial and error, low ambient humidity and infrequent misting during flower keeps my ladies from heat damage and mold. When misting or foliar feeding, the water drops act like little magnifying glasses, burning the leaf tissue. (which is why I only mist the lower sections of the plants)

    The below pix is link I posted from 2005 on another site, when I lived in Vegas. 100 to 110 degrees daily in the garage (where the flower room was, late spring temps) no a/c, and misting only once or twice a week, if that. 3 gallon pots, in soil, and I believe it was 37 grams average for the topped (shorter, 2 cola's) and 43 grams average for the un-topped. (single cola) Pix are in the link below. I can't really say what the yeild is on my spring/fall grows, as I don't have a scale any more. I truly see that it takes a bit longer to finish, but yeild seems approx. the same.
    Keep in mind, too...this is a 80% indica x 20% sativa mix. (ReeferMan's R&D #1 med. strain) Big, wide leaves. My Potent Purple and Swazi strains (both sativas) grow even better under warmer conditions. Don't know if it's the narrower leaf structure, the genetics, or both, but they handle the heat very well.
    Anyway, below is the picture and the original grow report link.
    (my username there was ThunderLungs)
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    Those look wicked good.
    How much did you find you were watering them?
    It stands to reason that strains whose heritage lies in more arid climes would handle heat better.

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    Thanks Stinky. Hope you don't think I was attacking your knowledge base, as this wasn't my intent. I truly have learned shitloads of valuable info from you.

    In the summer, I water in the mornings, and can go thru 3/4 or so of a gallon daily in the 5 gallon pots. 1/2 gallon or so in the 3's. By the next morning, pots feel almost empty, and soil is sufficiently dry. Tiz one of the reasons I dont water to the point of run-off. Am afraid of flushing nutes unnecessarily. Also...I give half strength nutes, twice weekly instead of just once, to make up for volume of water being used. Flushes every few weeks.

    Wow...I just read my RM post again. I sure was inexperienced with terminology, back then.

    Anyway, I, thru a mid-winter series of catastrophies, will likely be growing the Pokerface and a Swazi or two come summer time. Will start a log, (including temps, lol) when they're ready for flower.

    I did a cursory search yesterday, trying to find out the elevations of Swaziland, Africa. (the assumed geographical source for the Swazi Skunk) Elevation maps say it's from approx. 50 meters, up to 1500 meters. So not sure if my theory about the skinnier leaved strains coming from hot, arid climates is valid.
    Last edited by Rusty Trichome; Feb-20-2008 at 11:43.

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    Quote Originally Posted by Rusty Trichome View Post
    Thanks Stinky. Hope you don't think I was attacking your knowledge base, as this wasn't my intent.
    Aw knock it off. I'm not worrying...

    Quote Originally Posted by Rusty Trichome View Post
    In the summer, I water in the mornings, and can go thru 3/4 or so of a gallon daily in the 5 gallon pots. 1/2 gallon or so in the 3's. By the next morning, pots feel almost empty, and soil is sufficiently dry. .... Also...I give half strength nutes, twice weekly instead of just once, to make up for volume of water being used.
    This is why you are so successful in low %RH. Your watering/feeding schedule is exactly what you should be doing to make up for the dry conditions. The plants are actually raising the humidity themselves with a lot of that water you are giving them, like leafy green humidifiers.

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    Aww, Stinky...

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    Quote Originally Posted by Rusty Trichome View Post
    when I lived in Vegas. 100 to 110 degrees daily in the garage

    no a/c, and misting only once or twice a week, if that.

    3 gallon pots, in soil, and I believe it was 37 grams average for the topped (shorter, 2 cola's) and 43 grams average for the un-topped. (single cola)

    this is a 80% indica x 20% sativa mix.

    So not sure if my theory about the skinnier leaved strains coming from hot, arid climates is valid.
    That is pretty amazing dude, 110F! My plants stopped growing around 85-90 and my humidity is rather higher I think. At least the outdoor humidity sure is! I wasn't misting though... will try that

    How long did they take start to finish? I didn't see anything about them temps in your log..lol

    Regarding your theory, it may have some significance. In hot, dry climates, plants adapt to have a much higher volume to surface area ratio

    In climates with less sun and plenty of moisture, plants do best with very broad leaves, thin leaves, with a much greater surface area than volume

    peace

    O dude, and by the way.... from your thread, that grow was damn dialed in dawg!

    No wonder they decided life was peachy despite the heat.

    I was actually quite surprised you used two HPSs wth the garage already being 110F though.

    peace
    Last edited by melodious fellow; Feb-21-2008 at 18:48.
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    Quote Originally Posted by melodious fellow View Post
    How long did they take start to finish?
    I had to put them into flower a bit early, as we were preparing to move. 28 days veg, plus germination. Flowered to the point in the pix for 40 days.

    Quote Originally Posted by melodious fellow View Post
    I was actually quite surprised you used two HPSs wth the garage already being 110F though. peace
    85 - 90 degrees outside would cause 100-110f in the closed garage. Would get up to 130-140 in there, during the summer.

    During the summer months, I stagger the lights. Kinda like a light mover. Lamp 'A' on for 6 hours, just before it turns off, lamp 'B' comes on for 6 hours. (floro's on for steady 12 hours) Aggressive fans, low humidity, and raising the lights when need arisis.

    Still works for me where I am now, but now I have an air conditioned shed.

    In regards to being dialed-in, I had a bunch of online help, and a local grower to get advise from. altho he was a hydro man, was still able to insist I get the knowledge, equipment and supplies I needed, and avoid the gimmicky bs.

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    Quote Originally Posted by Rusty Trichome View Post
    85 - 90 degrees outside would cause 100-110f in the closed garage. Would get up to 130-140 in there, during the summer.
    Hey Rusty,

    Seeing that you're dealing with warmer temperatures pretty frequently, have you ever supplemented C02 to your growroom? If this has already been answered, please accept my apologies for bringing it up again. I'm just curious because temps get raised quite a bit around here during the Summer months, maybe not quite as high as yours, but still pretty warm around HIDs. I'd like to consider throwing in some C02 during the warmer months, but I've only done it once... and I didn't know what I was doing.

    I know you've said that you're on a fixed income, so you may not be using it now... but have you ever successfully tried it in the past? Also, hope everything is going OK over in your neck of the woods... heard there was a 6.0 quake not too far from you recently.
    Quote Originally Posted by stinkyattic View Post
    Switch to 24/0 light schedule and don't worry... about a thing... every little thing... gonna be all right.
    Quote Originally Posted by Rusty Trichome View Post
    It can be a fine balance between "ok...I need to water later today" and "shit...I should have watered yesterday."
    Plant problems? Fill out the Troubleshooting Form BEFORE asking how you should fix it!

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    Sorry, no CO2 experience. All I grow is for wife and I only, so never a need/desire to invest in that kind of stuff.
    I don't even use cool tubes, or anything like that. I have played around with a sheet of plexiglass hanging directly under the lights as a direct-heat barrier, but not really sure it helps much. Still adds to the ambient temperature.

    The quake was in northern Nevada. I'm just south of southern Nevada, (Arizona) and didn't feel a thing.

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    Quote Originally Posted by Rusty Trichome View Post
    Sorry, no CO2 experience. All I grow is for wife and I only, so never a need/desire to invest in that kind of stuff.
    I don't even use cool tubes, or anything like that. I have played around with a sheet of plexiglass hanging directly under the lights as a direct-heat barrier, but not really sure it helps much. Still adds to the ambient temperature.

    The quake was in northern Nevada. I'm just south of southern Nevada, (Arizona) and didn't feel a thing.
    No worries, my friend. You're apparently doing very well without all the extra goodies, so that's something for me to aspire to, too. I don't grow for profit, same as you I just do it to share with my wife and a few close friends, but there's still something in me that's always wanting to try the latest and greatest gimmick on the market... as opposed to sticking with what works.

    I've never built a cooltube either, because I've got an array of different sized lights laying around. I have, however, used a Cool Sun hood from Sun Systems, and when air-cooled, these things work awesome. If you ever decide to invest in a sealed reflector, I'd highly recommend one of these.

    Glad to hear the quake didn't rattle ya around! Take care.
    Quote Originally Posted by stinkyattic View Post
    Switch to 24/0 light schedule and don't worry... about a thing... every little thing... gonna be all right.
    Quote Originally Posted by Rusty Trichome View Post
    It can be a fine balance between "ok...I need to water later today" and "shit...I should have watered yesterday."
    Plant problems? Fill out the Troubleshooting Form BEFORE asking how you should fix it!

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    sticky,hi & rusty ive personally killed 2 crops of young uns.combine 20% humidity with rapid airexchange and heat u make plant jerky no crap every plant dead overnite

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    Mr. C. - If I could afford it, would go with the air-cooled hoods, or cool tubes. Would be a big help. But am ok where I'm at with them. Seems winter is worse for my ladies, tho. Just keeping the nighttime temps above 60f is costing a small fortune. (900w all night, every night) Costs more than running the lights. Spring is coming soon, tho.

    theelectrician: Best to understand what you are trying to put the ladies thru, and how to adjust your equipment and nutes, to better suit thier needs.
    For instance:
    start young ones indoors where temps are reasonable and they are strong enough for the transition, you don't nute full strength, you adjust the lamp height to suit the situation, you prepare the soil to retain moisture better, cool air agressively blowing back and forth on them, water daily...
    Just slapping them in a dry, windy sauna, without any preperation...of course they fry.
    Last edited by Rusty Trichome; Feb-23-2008 at 09:59.

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