Mould chart Temperature & Humidity

[Amnesialocal]

 

Hi all,

 

I have in my mind this chart since long time and I thought could be very usefull to share with everyone and have your opinion about it.

Apologies if this topic has been discussed previously. Also sorry for the webpage appearing, lazy me or thinking to keep the source.

 

What's take my attention is that apparently if we have temperatures around 29C and RH of 65% there is not risk of mould.

At 15.5 C Rh could be 72% without no risk.

 

Is there an opportunity for those growing under clouds to fight against mould  ( if the chart is correct).

 

What's your idea/experience about it?

 

 

[darXound]

Interesting chart! But, does it translate to cannabis? According to the chart, you could probably get away with 71rh at at 29C if i'm looking at it right

[Amnesialocal]

I asked myself the exact same question, and I arrived to the idea ( probably wrong) that what produce mould, fungi,etc it is more a combination between humidity and temperature as environmental condition, ( in which to me absence of ventilation is also the key) so, any "favourable" surface that respond to these caracteristics is potentially an incubator.

 

I saw a similar chart, actually several different in old posts ( I guess OG but not sure) disucssing it, but as usual I am not able to remember them.

 

29c 71% seems unrealistic isn't? Actually the perfect incubator.

Edited April 4 by Amnesialocal

[GSZZ]

34 minutes ago, darXound said:

you could probably get away with 71rh at at 29C if i'm looking at it right

 

If you were supplementing co2 beyond 1200 ppm you would have to run your temps higher than 29c, and your RH would have to be 75% or above due to stomata closing and water use efficiency going up (doesnt have to transpire as much due to there being so much co2 in the air) so it forces them back up but you don't lose so much water through transpiration.

 

 

as per the topic, high RH doesn't make for rot dew point does. Due to warm airs capacity to hold more moisture than cooler air, if the air cools too quickly in our grow rooms after the lights turn off, it doesn't take long for RH to creep up to 100% while the temps drop and when that happens moisture forms on surfaces - the dew point.

 

Its this moisture that forms on the surfaces that ultimately troubles us with rot as cannabis growers in two ways, the first is this moisture forms on the inside of flowers and it typically hits us at the end of flower because theres die back of the pistils. This moisture and the pistils that are dying back invite the rot in.

 

The other way, the name escapes me now, but its basically where theres no way for the water to escape the plant because they can't lose it through respiration at night because the humidity is too high, so it basically bursts the cell walls open (is it guttation?) for the water to escape, which invites the spores from the air in.

 

 

 

People often will lower their relative humidity, at the deteriment of their plants success, in an attempt to avoid bud rot but its a bit of a case of the tail wagging the dog as lowering RH lowers the dew point, on the other hand you can just warm the night time temps up to well above the dew point (which you can work out by using those online calculators)

Edited April 4 by GSZZ

[Amnesialocal]

48 minutes ago, GSZZ said:

as lowering RH lowers the dew point, on the other hand you can just warm the night time temps up to well above the dew point (which you can work out by using those online calculators)

 

That's an interesting point!! Thanks for the comment.

I take the opportunity If I can Calculating my situation:

27C 65%RH (last week vege)

Dew point is 19.8 C

So keeping the heat mat at 21C + heater at 23C I shouldn't have no risk of dew point =....the chart say No Risk of mould.

 

Now as you mentioned lowering RH means lowering the dew point. But is not this good?

I see as problem the fact that higher temperatures means higher the dew point.

So At 29C RH 65% Dew point 21.7C

 

I would goal

27C 55%

Dew Point 17.2 C

I am not sure if this means I could not using a heat mat

 

27C 45%

Dew point 14C

 

Not supplementing with CO2 ( I could artisanal DIY bottle style) which combination of temp\Rh would you suggest ?

 

Edited April 4 by Amnesialocal

[GSZZ]

35 minutes ago, Amnesialocal said:

Now as you mentioned lowering RH means lowering the dew point. But is not this good?

 

Only in that its not optimal for your plant because they lose too much water through transpiration (low water use effiency). Plants can't get up and move if they don't like where they are, the high movement and loss of water is an attempt to cool themselves down but it also has the effect of raising the relative humidity back up so they don't continue to lose too much water.

 

Instead of working against your plant by adding dehumidifcation, work with them by warming the nights up so they can have that higher RH during the day so the stomata stay open the entire lights on period and they can continually transpire - when the RH is higher and they don't lose so much water through transpiration, it means they can photosynthesize at a higher rate than at a lower RH because they're not trying to conserve water, ie, higher water use efficiency.

 

e2a also this means if you do it right, because plants don't transpire at night and water loss through respiration is small, relative humidity will be lower with the lights off.

Edited April 4 by GSZZ

[darXound]

1 hour ago, Amnesialocal said:

29c 71% seems unrealistic isn't? Actually the perfect incubator.

Oh absolutely, it's just that looking at the chart would suggest it takes 91 days for mould to appear which is way longer than a flowering period. Just making the point that perhaps a chart for crawl spaces might not be useful for flowers.

 

Are we not just safe if we keep our VPD in the proper range 

[GSZZ]

Just now, darXound said:

Are we not just safe if we keep our VPD in the proper range 

 

VPD is the result of transpiration not the driving force of it. VPD is just another tool for us to spot if theres an imbalance between the plants and environment.

[darXound]

11 hours ago, GSZZ said:

VPD is the result of transpiration not the driving force of it

Could you expand on that? It's my understanding that VPD is the result of temps + humidity = the potential for air to absorb water/plants transpiring.

 

This of course means transpiration will effect your VPD, but your environment should be adjusting for it - thus keeping optimum conditions (including staying out of the mould danger zone) 

[GSZZ]

52 minutes ago, darXound said:

Could you expand on that?

 

VPD is a way to determine how much water your plant loses through transpiration, light is the only thing that drives transpiration. Those charts that have green, amber and red zones are a bit misleading. The idea is you can use VPD to keep your stomata open the longest, so photosynthesis can happen without pause. 

 

 

[Amnesialocal]

4 hours ago, GSZZ said:

Those charts that have green, amber and red zones are a bit misleading

Interesting.

Your previous message to me was very clear using these charts.

27C at 45% and the VPD is at 1.85-2.02  ? Both chart and T69 controller)

Imho at VPD 2 the plant is evaporating too much water ...at least in my case last grow I had to water daily or twice during flowering in soil with this parameter and I was losing some bottom leaves due to water evaporation, without mentioning that small buds maybe we're linked to this.

The chart consider these values as a danger zone actually.

Maybe with CO2 implementation things are different.

 

Curiosity: in nature the majority of the places were cannabis grow are not actually tendencially more humid than dry?

Edited April 5 by Amnesialocal