[Speed of green]

im asking these quiestions because im trying to lower my risk for bud rot and powdery mildew.

Are temp swings only bad because the rh is increased as temps drop?

if humidity werent an issue would temp swings be a bad thing?

i have temp swings of mid 70's to low 60's with RH at a steady 50% and really good air circulation.

I have the ability right now to drop the humidity lower, however i cannot control the temp swings at the moment.

thanks for any input.

[getpulse.co]

The golden rule is provide a STABLE environment. Reducing swings of any type will provide a less stressful environment and give you a better end result. Concerning the relationship between temp and RH, you are talking about your, "vapor-pressure deficit, or VPD, is the difference (deficit) between the amount of moisture in the air and how much moisture the air can hold when it is saturated (source: Wikipedia).

Check this article and the chart it contains for out for reference.

[Limeygreen]

Difference between day night temperatures can be important. As the plant respires it does not require to have the same temperatures while photosynthesizing and transpiring, no light don't need the same temperatures. Some crops require large day and night differences to push for a generative growth, fruit set and size (tomatoes, cucumbers for example) while some flower crops prefer 1 or two degree difference to avoid excessive stretching (ie gerberas) but this depends on your goals etc. The cooler you run during the night the slower your respiration goes, the bigger the difference the more generative you go but if you stay too cool for too long you can also end up with weaker plants as they have slowed down and lose growth and yield potential.

As far as humidity goes, two important things, large spikes and valleys will promote more fungal growth, the more consistent you are the less likely this is to occour. Generally speaking during a night period you can be a bit higher in your humidity as the plant is respiring say 5-10% higher but to be on the safe side I would just keep the same humidity during your day as you are able to do so already, just because it is a safe bet. The next thing to concern yourself with is dew point, the close you are to dewpoint the more chances you can end up with botrytis and mildew, avoiding being close to dew point is critical for any crop.

For diseases that sporulate a good rule of thumb is, when it's damp they set up camp, why it's dry they fly, this is why the spikes and valleys contribute to spread of infections.

[Speed of green]

Originally Posted by getpulse.co

The golden rule is provide a STABLE environment. Reducing swings of any type will provide a less stressful environment and give you a better end result. Concerning the relationship between temp and RH, you are talking about your, "vapor-pressure deficit, or VPD, is the difference (deficit) between the amount of moisture in the air and how much moisture the air can hold when it is saturated (source: Wikipedia).

Check this article and the chart it contains for out for reference.

Thanks for the reply, i am familiar with vpd and my environment never hits the dew point, even right after lights out my humidity never spikes, the dehumidification and air movement keep all areas of my rooms the same temp and RH.

i understand that keeping temp and rh stable the entire time is the standard advice, i was just curious if temp swings were detrimental for any other reason than humidity/dew point issues.

Originally Posted by Limeygreen

Difference between day night temperatures can be important. As the plant respires it does not require to have the same temperatures while photosynthesizing and transpiring, no light don't need the same temperatures. Some crops require large day and night differences to push for a generative growth, fruit set and size (tomatoes, cucumbers for example) while some flower crops prefer 1 or two degree difference to avoid excessive stretching (ie gerberas) but this depends on your goals etc. The cooler you run during the night the slower your respiration goes, the bigger the difference the more generative you go but if you stay too cool for too long you can also end up with weaker plants as they have slowed down and lose growth and yield potential.

As far as humidity goes, two important things, large spikes and valleys will promote more fungal growth, the more consistent you are the less likely this is to occour. Generally speaking during a night period you can be a bit higher in your humidity as the plant is respiring say 5-10% higher but to be on the safe side I would just keep the same humidity during your day as you are able to do so already, just because it is a safe bet. The next thing to concern yourself with is dew point, the close you are to dewpoint the more chances you can end up with botrytis and mildew, avoiding being close to dew point is critical for any crop.

For diseases that sporulate a good rule of thumb is, when it's damp they set up camp, why it's dry they fly, this is why the spikes and valleys contribute to spread of infections.

thanks for this detailed information, i will hopefully be able to correct my temp issues in the coming weeks when my pellet stoves arrive. until then i will continue to dehumidify and make sure im nowhere near the dew point.

do you know what percentage RH i should aim for below the dew point of any given temperature to reduce the risk of mold and mildew?

[Limeygreen]

https://dpcalc.org/

[Speed of green]

Thanks, thats really useful.