Believe as you wish it matters little to me. I am quite sure if you read 10 different books you would ger at least 5 different opinions. If you inquaired of 10different horticultaro islists u you would likely get just as mixed of an opinion. As for Ed he is as often wrong and opinionated as anyone else. As for clogged stoma from aeration t is a qi uite common problem. As for plants stomas closing due to low humidity. Takes a lt less than 40% humidity for that to happen. As for tarnsporation and respiration being reduced by high humidity. That is pretty common knowledge. Reduced transpiration and respiration means reduced growth. I do know that 40% is not too low but 60% could very well be too high. I prefer not over very well.

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Sounds to me that around 50% for everything works for you. OK by me but I feel a new grower is better served to let the plant breath as best it can as to not limit growth. Extremes are generally bad but I don;t think 60-70% is all that extreme. I use to not consider humidity when I was first growing but personal experience with the same strain has shown me the benefits of providing a little higher humidity during veg. Seems to make it stronger with bigger stems. In nature it is generally wetter in spring than in the budding summer months and inside grows are trying to emulate nature.

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so I guess Roseman, MostlyCrazy, Major Tom, Southern HomeGrower, JonnyBtreed, Greg Green, George Cervantez and Ed Rosenthal are all wrong about proper humidity, and fatman is correct!

Hhhhhmmmmmmmmm?

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In the summers around here we normally get up to around 75% 80% humidity on a regular basis during the plants entire life cycle, and I'll tell ya one thing. It certainly grows VERY, VERY well outdoors around here.

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I thought the high humidity of mountain areas like in Bolivia was supposed to be great for growing, too.

My plants like to pretend that they are in a rain forrest and get a daily shower often, in Vegging...except we call it Misting.

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Misting my new grow every day and a couple of times a day sometimes because I forget if I did mist them. The Stoner's lament! I gonna have to start some sort of tag system shortly! LOL!

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I teach how to Grow without Ground

This is the aeroponics section is it not. It is understandable that many a soil grown plant can use some increased humidity as they in genral transpire and respire less in than an aerponic plant. There is so much being called hydoponic (rock wool, hydroton, mixed soil less, rocks, gravel, coconuts fragmentsm ground up rubber tires) that it is even easy to believe that some hydoponics can use some extra humidity as their transporation and respiration is also less than that normal to aeroponic growing plants. However, there is something wrong with an aeroponic grow set up when ithe plants in it actually benefit from a humidity of 50% or 60%. I do not grow soil and haven't for over 25 years so I rarely give input in that area and fail to see why it is being addressed in this section of the forum.

A certified horticulturalist and arborist. Does that mean a typical masters or Doctorates degree as in the science of horticulture normally possessed by a "Horticulturalist" actually involved with scientific research in horticulture and advancement in the studies of horticulture. I don't believe a certificate is ever really based much upon any large degree of formal education even at an associates degree level. Of course I could be wrong.

As for buying a shelf full of pot growing books. I prefer books written by people who have professional degrees and who have published research papers. We all have are individual preferences though, that is obvious. As for the names touted I guess as experts, the only one that even sounds familar is Ed and thats because I remember his name from the late 70's and early eighties when I was young and bought magazines such as high times and such. I now buy professional reference books not magazines. I have not found the need to waste my money on such magazines for a very long time. It takes about an hour of scanning and spot reading to gather what little new or relevants information that is ec ver avilable in books such as pot growing books and high times. If even that long.

Most Pot growing books I have seen just seem to mainly be a regurgitation of what is already been online. Likely there is much more up to date material in these forums than in most of the books ever written. The videos are no better. There is definitely better information on Google Scholar or at your local university than in most Pot growing books and magazines. And, Roseman, like I said I never heard of your name or any of the others but Ed's. Go figure, as I have been growing for over 35 years without needing any of those writers books. Sorry, the books I read are just written by those with science degrees in horticulture, biology and other applicable science degrees. My students bring some pot books and magazines in at times, that is more than enough.

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Al we know is that it was reported that high humidity in veg is an advantage, tried it ourselves and it seems to work. Then we keep doing what is successful for us. Have you tried a low humidity vs high humidity in veg and not noticed a difference? I'm thinking that the increase in info is due to more growers and their experiences. Well that and the internet makes all books sort of obsolete the day they are published and they are aimed more at commercial grows then the home enthusiast but that is changing as we type.

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OK, this is how I understand transpiration and relative humidity. Most plants are about 90% water. Water is responsible for or helps with many things: it keeps the plant cells inflated (known as turgor); it serves as a transport medium for nutrients; it’s responsible for cooling leaves as it evaporates from leaf tissue during transpiration; and, with regards to this post, it serves as the regulator of stomatal opening and closing, thus controlling respiration and photosynthesis. For growth to occur photosynthesis must be greater than respiration.

Like everything else, I believe you try to achieve a balance between several factors to produce optimum humidity conditions for the PARTICULAR STRAIN YOU ARE GROWING.

The first factor you need to worry about is the particular plant you are growing. Different plants like to grow in different temperature ranges; if the temperature is outside of the range it likes to grow in then photosynthesis and respiration will be affected. So you need to determine the particular temperature range your particular plant likes.

The next factor you need to worry about is the thermoperiod, or the daily temperature range. Plants grow best when daytime temperature is about 10 to 15 degrees higher than nighttime temperature. Under these conditions, plants photosynthesize (build up, grow) and respire (break down, get rid of waste) during optimum daytime temperatures and then curtail respiration at night. Remember, for growth to occur, photosynthesis must be greater than respiration. The rate a plant photosynthesizes is dependent on the temperature a particular strain likes to grow in. If it’s too cold during the day for the plant photosynthesis (and therefore growth) is slowed; if it’s too hot then respiration increases (to help cool the leaves) to the point that it exceeds photosynthesis and growth is slowed.

The next factor is relative humidity,which is the ratio of water vapor in the air to the amount of water the air could hold at a particular temperature and pressure. Warm air can hold more water vapor than cold air. Basically, to compute relative humidity you take the amount of water that is ACTUALLY in the air and divide it by the amount of water the air COULD hold at a particular temperature and pressure.

Water vapor moves from an area of high relative humidity to one of low relative humidity. The greater the difference in humidity, the faster water moves. This factor is important because the rate of water movement directly affects a plant's transpiration rate, and its transpiration rate is directly related to its growth rate.

The relative humidity in the air spaces between leaf cells approaches 100 percent. When a stoma opens, water vapor inside the leaf rushes out into the surrounding air, and a bubble of high humidity forms around the stoma. By saturating this small area of air, the bubble reduces the difference in relative humidity between the air spaces within the leaf and the air adjacent to the leaf. As a result, transpiration slows down.

If wind blows the humidity bubble away, however, transpiration increases. Thus, transpiration usually is at its peak on hot, dry, windy days. On the other hand, transpiration generally is quite slow when temperatures are cool, humidity is high, and there is no wind.

So, in general, the plant will grow best with high humidity conditions…if that’s ALL we had to worry about, then I would say you would always want the highest humidity possible with no air movement, even during flowering, especially if you were growing in higher than optimal temperatures. But that’s NOT all we have to worry about. We NEED to supply air movement: it refreshes the CO2; it evens out the air temps in the grow area; it helps prevent insect and mold infestations; etc.

And since we need to supply air movement and often grow in higher than optimal temperatures, we need to increase the amount of humidity in the air to decrease the difference in the relative humidity of the leaves and the relative humidity of the air, thus slowing respiration and increasing photosynthesis and growth.

But as we increase RH we also increase the plant’s susceptibility to the likes of mold, especially in densely packed plants that are flowering. So we must achieve a balance between increasing the plants growth rate through increasing RH, while decreasing the plants susceptibility to mold with air movement at the same time. You can experiment by increasing your RH and decreasing your air movement until you get mold, OR YOU CAN GO WITH WHAT THE EXPERTS SAY ARE THE OPTIMAL RH CONDITIONS FOR GROWING WEED…it’s your choice…

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Or you can change things up by using CO2 is is quite often used by aeroponic growers and also deal with the aspect you left out. This make no sence. "The relative humidity in the air spaces between leaf cells approaches 100 percent. When a stoma opens, water vapor inside the leaf rushes out into the surrounding air," (Water does not rush out as there is already moisture there and the new water is not going jump out into go to a highly saturated area but will instead stay within the plant.) and a bubble of high humidity forms around the stoma. By saturating this small area of air, the bubble reduces the difference in relative humidity between the air spaces within the leaf and the air adjacent to the leaf. Now yu print the obvious result of over humidificaton."As a result, transpiration slows down. (Yes as you say when there is high humidity then transpiration slow down). Lower the humidity to a reasonable level and the plant can more easily transpire as there is a lower level of humidity. Unless you are running a poorly balanced system there is no gain to lowering transporation because there will lawys be the capability to have adequate transporation capabilty with the lowered humdity if CO2 and a good water/nutrient system is supplied. Of course you can have too litte humidity , just as you can have too high of humidity. However 40% is not too little but without a fan andventilation a humidity of 50% to 60% can lower transpiration meaning it can easily be too muc. My points is there are too many old practices being used that were based upon opinions that have found to be wrong. Just as with a humidity of say 40% you can do without the unneccesary fan that can actully domore harm at a humidity of 40% and therefore requires higher humidity to be used safely. Lower the humidity and do way with the fan and aertaion. Get an airconditioner and a CO2 system. Don't push humidity levels used for low tech systems as the only proper levels on better high tech systems just because they work with the low tech systems with overlighting and excessive heat, and overventilation etc, etc. I would hpoe those system are becoming less common. Maybe you should instaed be writing if you are going to over light a system, and also have a poor water/nutrient delivery system, then you will likely also need to over ventilate, over humidify and over circulate your air. There is the fact that that the fan is just not needed with a humidity of 40% with CO2 and aeroponics[good hydroponics with temperature control. What people find necessary in an imbalanced system with too high temperatute due to overlighting, and iandequate water nutrient system such as poor hyroponic systems and soil systems has nothing to dow with the fact that with a well balance system a humidity in the 50% to 60% range is not an advantage but actually skows transpiration and growth, as reduced transpiration means reduced growth. There is no benefit to lowering transpiration in a well balanced system. Your just combining inadequate low tech practices with a few higher tech features like HID lighting then using higher humidity am nd ventialtions as a crutch or inadequate bandaid. All to continue to say that high humidity is better. I agree high humidity in a poorly balanced system might have advantages, but I would think it better to improve the system rather than use bandaids. High humidity is merely a bandaid.

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