Moabfighter
Well-Known Member
If your soil is that dry on top your air humidity is simply not where it needs to be for veg.
VPD = PAIN
- Thread starter GemGrows24
- Start date
MtRainDog
Well-Known Member
I doubt his soil is hydrophobic so early on. And the OP said it's pretty wet below the surface. My guess would be the soil is just a little too wet underneath, and the roots are a bit saturated, and not having to go look for more water in the soil. The temps and humidity all sound fine, though personally I think 70% rh is a bit crazy unless sealed room with CO2. I'm lucky to hit 50% RH ever in my room. Plants don't seem to mind it one bit though.
If it's not an auto, you can dig it up and check the root ball for more definitive answers. If you have a solid, soggy lump around the roots, it's too wet.
If it's not an auto, you can dig it up and check the root ball for more definitive answers. If you have a solid, soggy lump around the roots, it's too wet.
Fatjoe
Well-Known Member
Fail safe method of watering is weight. That moisture meter finger is not the answer. Water then pick up the pot. Only water it when it becomes lite.
Eventually you'll be able to visually see a plant needs water before it's dry. It just comes with experience.
I think your doing great and learning as ya go. New growers just gotta find their stride. Only way is hands on and your definitely doing that.
Vpd...stop worrying. Just keep your humidity at acceptable levels for veg or flower and you'll be good. I ignore vpd.
Eventually you'll be able to visually see a plant needs water before it's dry. It just comes with experience.
I think your doing great and learning as ya go. New growers just gotta find their stride. Only way is hands on and your definitely doing that.
Vpd...stop worrying. Just keep your humidity at acceptable levels for veg or flower and you'll be good. I ignore vpd.
VPD is the same thing as temperature and RH - it's just one number instead of two.
"Once you get dialed in with everything else then start tweeking VPD"- if you get your temperature and RH "dialed" in, those numbers will result in an "optimal" VPD figure because VPD is nothing more that one number to express a range of temperature and RH values.
A lot of growers don't understand that. It's as if VPD was some magic number that made the wolves lie down with the lambs. It's not. VPD is just "feels like" temperature for plants. There's nothing to "chase" in VPD. It's just "feels like" temperature for plants.
The real value of VPD is that it indicates how much water is leaving your plant because that's how much water is going into your plant. In hydro, high VPD isn't as big an issue as in soil because, if you're in soil and if your plants are pushing to 10%, 50%, or 100% as much water as they were a few days ago, then not-good things can happen if the plans don't get more water and/or reduced EC.
A lot of the "nutrient issues" that crop up are VPD based and that's for the simple reason that, when VPD is high, transpiration is high and, since nutrients are taken up when water is taken up, if VPD is high, there's an increased likelihood of nutrient issues. If you're not aware of the fact that your plant is taking up a lot of water, there's a chance that the plants will run into problems.
On the other side, there is no need to go to extremes to create a "perfect" environment. We know that 0.8, 1.0, and 1.2-1.4 are considered optimal VPD for cannabis in seedling, veg, and flower but cannabis will do fine if it runs at, for example 1.2 in veg or 1.6 in flower.
VPD is nothing to "chase". It's just "plant temperature" and having VPD too high (too warm and dry) is a common cause for nutrient issues.
GreenGenez421
Well-Known Member
Your forgetting about the leaf temperature offset. It's a critical input to calculating VPD. Without it, what's the point of monitoring VPD?
I will agree with you however that VPD is the cause of alot of nutrient issues. But this is because a sizable chunk of growers can't control it properly. If you could, you'd know.... it will take your grow to the next level.
GemGrows24
Member
Exceptable as in 40-70% range . I've been between 55 and 70 lately plants seem to stand more firm in in the higher humidity . But idk if that might change as the plant gets bigger. Would I slowly lower the RH till flower? Or keep it at a set number?
GemGrows24
Member
This was kind of my point entirely. I've been focusing on humidity and temp separately but just recently started to pay attention to the relationship that has with plant transpiration. I understood when I first started you need to have humidity and temp in a generally range. But know I'm understanding how tweaking each individual number effect VPD calculations. The reason I thought maybe my VPD has been the issue is because I assumed my high VPD meant the plants were drying out quicker then they can uptake water. But maybe it was more of a watering issue than a VPD issue specifically
GemGrows24
Member
my humidity hasn't reach lower than 55 consistently currently running at 65-70 I think I'm seeing some difference in canopy moisture but it's hard to say as I need more time to tell.
GreenGenez421
Well-Known Member
@GemGrows24. Do yourself a favor if your going to dabble with VPD, pick up a infrared thermometer gun. They're pretty cheap for a basic one. But it is important to know what the leaf temperature is. When plants transpire, the leaf temp is actually 4-7 degrees Fahrenheit less than what the ambient temps are. Even if your not trying to tweek VPD, the leaf temp can give you some insight as to what the hydrostatic pressure is within the soil. And to prove my point, buy a temp gun and scan random fan leafs, youll notice the leaf temp will rise to that of the ambient temp when the soil is dry. Once you water, scan an hour or 2 later and you'll notice the leaf temps drop below your ambient and so you can visually confirm your plants are actively uptaking water. That and the fact that your ambient RH will also rise when the plants are actively transpiring.
GemGrows24
Member
Thankyou! I was actually gonna ask how people got the leaf temp. I assumed those laser temp guns were what I needed. Thankyou for confirming that . If I had one right right it would def help me confirm if the plants properly uptaking water or if it's possibly too dry. It's been a couple days since my post and I think I'm already seeing some more sturdiness in the plant where as before it seems a bit droopy. I also bottom water for the first time yesterday.
That way if I did overwater the soil wouldn't take it. And if I underwatered the plant could take what it needs. The pot soaks up the two cups I had poured almost immediately. Given some dry spots. I feel the big pot and small plant in it has created room for dry spot in the soil. I'd imagine bottom feeding helps evenly distribute moisture through the soil so from now on I'll only bottom feed and spray the top layer to assure even moisture. Thankyou guys for the help all is appreciated as I'm trying not to give up at least twice a week.Patience was never my specialty haha I'm learning however
GemGrows24
Member
GemGrows24
Member
new growers syndrome should be a real diagnosis just saying lol.
medidedicated
Well-Known Member
It is lol. Its called helicopter growing. Itll go away.
GemGrows24
Member
If I had kids they'd be on leashes . I'd be that parrent and I'm definitely that grower
pegboy
Well-Known Member
That plant is not that far behind. It should be fine. Plants rarely hit perfect VPD in the wild.
"I assumed my high VPD meant the plants were drying out quicker then they can uptake water." - that's all that VPD is. It's the difference between the water pressure in the plant vs the water pressure in the atmosphere. It's physics applied to agriculture.
As you're saying, it tells us how quickly water is leaving the plant so it can be helpful to growers who want to ensure that their plant has enough water available, and, second, that, if the VPD is high, it might be good to reduce the fertilizer level in the water to avoid nutrient issues.
"But maybe it was more of a watering issue than a VPD issue specifically"-you hit it on the head. They're different sides of the same coin.