vpd questions

[tipper619sd]

I was using the chart and saw that it said for optimal growth it need s to be at the .85 range. I have a uc and i was kinda worried that at 85 temp and water temps at 66 and ppms at 500 my rh had to be at 80 to be optimal kinda scary to do any one done this before all help is wanted and appreciated thanks farmers.

 

[Seamaiden]

VPD is the interplay between temperature and humidity. Adjusting temperature can have an effect on VPD, not just adjusting RH.

But, before you go messing with anything, what are your girls telling you?

 

[tipper619sd]

Well my leafs where the flowers are are all down and curling. I dont know what to do to keep the rh up im so lost

 

[Unit541]

You are correct sir. When my temps are around 85, I keep the RH at (well, as close as possible) to 80-82 or so, and they absolutely love it. It seems it is time for you to add a humidifier or two. Use only Ultrasonic units, use R/O in them to keep the discs deposit free, and try to avoid digital ones, as they will not come back on after power has been lost. My space is 6 feet by 14 feet, 8 foot ceilings, and when plants are small, I need two of the cheap ($45) Vicks ultrasonics to keep my RH at 80 with a 1 ton A/C unit set to 83 (allows for 85-86 at the canopy). Once the ladies grow up, there's enough transpiration taking place that I can put one away and maintain 80% with only one. My room is sealed, which plays a huge part in keeping the moisture in (damn CO can be du-rye).

It can be a tricky balancing act, as sometimes it's difficult in any given setup to maintain those RH levels, leaving additional cooling as the obvious solution (get temps down to correct vpd rather than get rh up). The problem with this, is the moment you add more A/C, you draw even more moisture out of the air with the cooling.

In my personal experience, the difference in growth rate between 60% and 80% RH is astonishing. I almost vomit every time I hear some arm-chair "expert" tell a novice to get their grow room to 50% RH and leave it there.

 

[Jalisco Kid]

Check out faran 707's. Sonic fogger's do not last or keep up with summer temps. I would look at temps around 78* and rh around 65% lights on 45-50% lights off. Most rooms are not dialed in to run rh over 70% due to lack in ventilation. Lower humidity at night will help your girls health. JK

 

[bangbang]

You are correct sir. When my temps are around 85, I keep the RH at (well, as close as possible) to 80-82 or so, and they absolutely love it. It seems it is time for you to add a humidifier or two. Use only Ultrasonic units, use R/O in them to keep the discs deposit free, and try to avoid digital ones, as they will not come back on after power has been lost. My space is 6 feet by 14 feet, 8 foot ceilings, and when plants are small, I need two of the cheap ($45) Vicks ultrasonics to keep my RH at 80 with a 1 ton A/C unit set to 83 (allows for 85-86 at the canopy). Once the ladies grow up, there's enough transpiration taking place that I can put one away and maintain 80% with only one. My room is sealed, which plays a huge part in keeping the moisture in (damn CO can be du-rye).

It can be a tricky balancing act, as sometimes it's difficult in any given setup to maintain those RH levels, leaving additional cooling as the obvious solution (get temps down to correct vpd rather than get rh up). The problem with this, is the moment you add more A/C, you draw even more moisture out of the air with the cooling.

In my personal experience, the difference in growth rate between 60% and 80% RH is astonishing. I almost vomit every time I hear some arm-chair "expert" tell a novice to get their grow room to 50% RH and leave it there.

Wow... Just like you said. I can't believe I though RH should just be at 50%%%. Further more how have I never heard of Vpd???? Thanks guys. Question: I found this chart.
..

Do you think this chart applies to rooms running CO2... And at what point in flower do you not use these charts? I would be worried about mold. if I were running at 75 f with 65% rh...
thanks

 

[woodsmaneh]

Wow... Just like you said. I can't believe I though RH should just be at 50%%%. Further more how have I never heard of Vpd???? Thanks guys. Question: I found this chart.
..View attachment 313259


Do you think this chart applies to rooms running CO2... And at what point in flower do you not use these charts? I would be worried about mold. if I were running at 75 f with 65% rh...
thanks

No this chart does not apply to CO2. Run your room as close to 85 as you can with CO2 and keep your RH above 60% till the last 10 days than just let is go where it wants. No CO2 for the last 10 days! keep it at norm 400 to 440ppm.

VDP is a very important part of growing but I never get my panties in a knot over it, just like pH I have a range 5.4 to 6.2 and do noting as long as it is inside that range. Same with VDP I stay within a range for the first 7 weeks, for me that's 65 to 80% rh with temps at 85 with CO2. With no CO2 80 degrees and same RH

 

[cctt]

No this chart does not apply to CO2.

Why not?
Is there another VPD value that is more appropriate with enriched CO2 than the 8.5 shown on this chart? Should the chart have a third axis representing CO2 ppms?

 

[woodsmaneh]

Why not?
Is there another VPD value that is more appropriate with enriched CO2 than the 8.5 shown on this chart? Should the chart have a third axis representing CO2 ppms?

The chart should have a third axis for CO2, the chart is based on ambient CO2 levels which are around 400 to 450 ppm

 

[Seamaiden]

Woodsman, how difficult would it be to create that third axis?

 

[ttystikk]

I disagree with the idea that vpd varies with co2 levels. I also found better results running at 80 degrees and 65-70% rh.

I run my rooms to that chart whether I use co2 or not, and I get quality results every time.

If you live in a dry state like Colorado, DITCH THE AC! Trade up to a big chiller instead, since not only do they not dry your room out, they are about twice as efficient to run at high altitudes and low humidity. The only place I need a humidifier is in my veg tent, which isn't a controlled room- it's just a tent.

 

[purpleberry]

Highest temp I like to run is 78 on the wall, under the lights maybe a little hotter. And ill run the RH 65-70 starting out. And take the temp and humidity down slowly after week 4-5 to prevent mold. Im looking into setting up a controller or multiple dehumidifiers So I can run day and night RH settings. Id like to set night at 50 to start and 45 after week 5-6
Ive ran rooms above 80 and my cut don't like it, above 85 it really don't like it.

 

[darlingmaster]

How does one go about keeping mold at bay with RH in the 80% range?

 

[woodsmaneh]

How does one go about keeping mold at bay with RH in the 80% range?

real good air circulation will help big time.

Average daily temperature
Temperatures of over 15º C favour the development of the fungus and the spread of the conidia. In general, production of conidia is reduced at temperatures of below 15-20° C or above 26° C. According to studies conducted on hops, exposure of around two hours to temperatures over 32º C reduces the incidence of the disease.
Relative humidity
The optimum range for germination of the conidia is between 75% and 98% humidity. At relatively low humidity rates, the fungus reacts by releasing a greater number of spores. This dispersion is also favoured by sudden fluctuations in humidity. The more the ambient humidity falls and the more abruptly it does so, the greater the number of spores released into the air. Although the environmental humidity is low, due to plant transpiration the leaf surface may be quite damp, facilitating germination of the conidia.
In such cases, a digital temperature and humidity gauge with maximums and minimums is a must, since it will give you a precise idea of when these high-risk conditions arise.
These studies of l. taurica in hop plants have observed that the conidia germinate at temperatures between 10ºC and 35ºC, with an optimum temperature of 20ºC. More extreme conditions (6 hours at 40ºC) significantly reduce the viability of the spores (meaning that there is a reduced chance of infection in very warm areas in summer). It has previously been noted that the development cycle of the fungus depends on climatic variations and this is also the case here. While the optimum temperature for germination is 20ºC, no new spores form in infected plants at higher temperatures; however the optimum temperature for the growth of the mycelium is between 15º and 25ºC.
As for relative humidity levels, the most favourable conditions for germination are a day-time figure of between 85% and 95%, combined with very high night-time humidity. But although high humidity levels favour germination, they also hinder the development of the mycelium. The obvious way of ensuring that plants do not become infected is therefore by using a preventative treatment when the average temperature is between 10º and 35º and when relative humidity remains high during both day and night (such as during long periods of rain or frequent daytime showers).
If your indoor plant has already become infected (whether the symptoms are visible or not), you should ensure that you keep the temperature and humidity constant and without sudden variations. By keeping the temperature as high as possible (while taking care not to impair the development of the plant), you will help stop the formation of new spores and hinder the growth of the mycelium, thus preventing the disease from spreading. You should also use natural fungicide treatments regularly. This will prevent the release of new spores, or make them less viable, stopping the spread of the disease. At the same time, it will hinder the growth of the fungus.
Toxicity of the oidium

Turning to the intrinsic toxicity of the various oidium fungi that can attack hop plants, l. taurica and s. macularis produce no toxins that might be considered dangerous to human health. However, it is important not to forget about false powdery mildew or pink oidium, which even experienced growers find difficult to distinguish from the real thing. Indeed, scientific studies have been carried out to try to establish the difference between the two fungi on hops, so that they can be safely identified. This pink oidium, trichothecium roseum, produces a number of micotoxins which are highly toxic in mammals. Studies carried out in 1969 showed that extracts of this fungus at various levels of concentration were fatal to mice, rabbits and even 19-day-old pigs, as well as causing other adverse effects. Given how dangerous this fungus is, it is obviously critical to prevent the development of oidium on your plants and minimize the risk of consumption of contaminated plants.
Indoor plants

Infections in indoor plants are a result of conidia floating in from outdoors into the growing room, where they germinate and develop. Starting with a clean room, plants that are free from oidium (cuttings are silent carriers) and a new growing medium, your strategy should be to prevent spores from getting to your plants, and if any do manage to get through, to make sure they can't take hold.
Physical means of preventing spores from getting into the room. The number one way fungi get into the room is through the extractor fan. As you remove the air from your plants, it is replaced by the same volume of air from outside — which enters through the grille in the room and other apertures (e.g. beneath the door or through the bottom hole in the case of a cabinet), creating a current of air that goes all the way from outdoors to the interior of your growing room. The air that gets in through these grilles is not filtered, so that if the atmosphere is full of spores, you will be spreading them fast onto your plants. So it is very good practise to add air to your crops instead of removing it, and to pre-filter the incoming air, e.g. with a carbon filter or HEPA filter. The same volume of filtered air that you allow into the room will be released and forced out through the grilles or openings, creating a current of clean air going from inside the room to the exterior, further preventing the entry of any spores (and insects), which would have to go against the flow to get in. This is the same principle used by laminar flow chambers and other recipients that need good asepsis.
Clearly, spores can also get into the room on your clothes. It is therefore a good idea to get into the habit of having a coat or dressing gown to hand, which you can put on before you go in.
As if these physical methods were not enough, you can also apply preventative treatments, especially at the most difficult times of year. Remember that you can use sulphur throughout growth until the day before the plants start flowering. However, when in flower, the plant will begin to grow new leaves 15 days after the last treatment. These new leaves are no longer protected by the sulphur, so if you want to be sure of having good protection (especially in plants with a long-flowering period or at times of year when the risk of oidium is highest) you will have to use other products. In order for the treatment to be as effective as possible, you must know when the concentration of spores outdoors is at its height. Following the same rules as for outdoor crops, the greatest concentration of spores will occur on days when several of the environmental risk factors described above coincide (see Table 1). When these outdoor conditions occur, you should take preventative action on your indoor plants. Always spray the plants for a few minutes before turning off the lights.
You should also keep the humidity levels constant and unfluctuating we recommend keeping humidity levels low (below 60%). Note that this humidity is good in cases in which there is no fungus on your plants and you therefore want to prevent any spores that have got in from germinating. Using fans to keep the leaves in motion can prevent the spores from taking hold on the leaf.
Many growers make the mistake of dramatically lowering the humidity when they discover that their plants have oidium. However, this sends out a signal that stimulates the fungus already on the crops to scatter its spores with the result that the disease is propagated very quickly. If you have found this type of oidium in your grow area and it is not at a very advanced stage, you should remove the most infected leaves, keep humidity constant at around 70% and treat your plants every 2-3 days with a bio-fungicide (or as per the manufacturer's instructions). Likewise, it is not advisable to keep the leaves moving with a fan if the oidium has already taken hold; the only thing you will be doing is scattering the spores even further. Once the oidium has been eradicated, you can lower the humidity and turn the fans on again to prevent it from growing back, but you should always repeat the fungicidal treatment whenever the atmospheric conditions described above arise.
To keep the relative humidity constant you can use a hygrostat connected to an intensity regulator (a power meter). The system connects the extractor at maximum power (the extractor operates at top speed) when the humidity rises above the programmed rate. When the humidity is at the right rate or lower, the hygrostat connects the extractor fan but through the regulator, which means that the extractor operates at a lower speed, which can be regulated.

In all cases, stop applying the preventative or curative treatment one week before harvesting.

 

[indogro]

wow, so my temps are 82, but my rh in veg has been close to 40%. I guess it's time for some hums!