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Fiddynut's second run - Larry OG

Fiddynut

Active member
Greetings icmag users. I'm Fiddynut and this is my second grow. Actually I lie a little because I did try to get a second grow started a couple months ago. I was part way through my first grow and I had to abort because I thought I had some root aphids and wanted to be sure to eradicate them. As it turns out they were just a few fungus gnats I think.
With help from people here on these forums my first grow went great. I learned a lot and got just over 10 oz from the 3 plants I harvested. It far exceeded my expectations. The info I got looking through these forums and reeding about people's experiences gave me all I needed to get started. Once I got going I joined the forums and started posting. The advise I got helped my first grow be fun and successful.
I'm a month post harvest and it time to get back to work. I mis having plants to care for. On this grow I want to be more consistent with feeding, top and train my ladies some, and take cuttings and learn to get them to root. I have 2 seedlings out of 3 that sprouted. The third popped up but withered and died. I may have had the soil a but on the damp side. I will be replacing the #3 with another seedling of another strain ( cali connection GSC). It will be a few days behind the other 2.

A little about the equipment I'm using.
Veg tent is 2x4x6 with a 4 bulb (54w each) t5, inline duct fans for intake and exhaust and a 6" desk fan.
Flower tent is 3x3x6 with 4" ho canfan and carbon filter for ventilation, 600w hps with air cooled hood and 6" canfan to cool hood and a tower style fan inside.
Using fox farm happy frog soil in 6" pots transplanting into 14" pots for flower.
I plan on using the fox farm trio for nutes plus a few supplements like kelp and a few others.
I use water from a natural spring near where I live. It has a lot of good stuff in it and has a high ph. I used this water last time and my plants loved it. I never needed calmag or anything because the water seems to have a lot in it.

So the journey begins once again. One of the most challenging parts of my last grow was learning how and what to feed my plants. I under feed and switched nutes on my last grow so I want to really learn how to use them right this time. My eventual goal is to learn how to grow all organically but that will be down the road. For this and the next couple grows I'll be using the fox farms trio of nutes and maybe a few supplements. I don't want to be that guy with 30 bottles of plant food and no clue how to use any of it so I'm going to keep it as simple as possible.
My last grow went great but my plants were not topped or trained at all. This resulted in the natural Xmas tree shaped plants that had a lot of secondary buds that got less than max light because of the 3 higher colas. This time I want to top twice and try to get a better canopy of more but smaller colas. I'm looking forward to learning about and practicing training techniques.
I also want to focus on learning how to clone on this grow. I want to be able to to pick pheno's and re grow the ones I like best. This will be challenging for me because I'm so new to gardening.

I really enjoyed my first grow and I expect this to be as much or more fun. I expect to have challenges and learn a lot. I hope to gain experience and confidence.

Thanks for stopping to check this grow out! Feel free to comment or give advise and suggestions. And now a couple pics of the baby's.
 

pop_rocks

In my empire of dirt
hey hey buddy!
hope you dont mind if i walk in circles a few times and make myself at home

so this is the new grow!

the t5's are a new addition i think and are good choice for veg/cloning lights
so far the seedlings look like...seedling :)
off to a good start

sounds like you have some nice goals laid out for yourself
i def agree that cloning is the next step in your journey and you hvae a good light for it in that 200w t5

ive grown larryOG in the past and she is a knock out
heavy stone and nice buds
never grown out the GSC, so im very interested in how she comes along
once thing i like to do when growing multiple strains, is i use the colored electrician tape and make these little markers/ flags
(right now im using sections of chop sticks we got from take out)
i cut the chop stick ( or any thin wooden dowel) into small 3-4" sections, then i wrap a piece of colored tape around the end of each one

this gives me a quick visual marker to know which plant is which
plus they are easy to reuse and virtually free

really hope you have the success you enjoyed in the past and cant wait to see where this little adventure takes us!

/i dident forget about saying i would be posting some mountain bike pics too
oh and my mom said she might have this old meat grinder that i could have!
if thats not enough, the mrs just made some brownies!

im going to fire up a fat J and lets get this party started!

/plenty to go around and i hope others goin in the fun as well!
 

GastroGrower

Active member
Hey Fiddynut, glad to see you starting another thread. Great summary on what you've been doing and what you're looking at exploring in the future. Sounds like you learn through experience in the same way I do.

I'll be excited to see what your end result looks like with these OGs. If you do top or train them, you'll see a huge increase in your yield. Give them the right conditions and love and they'll definitely take advantage of it.

I'll be subbed to follow along, Good luck!
 

Fiddynut

Active member
hey hey buddy!
hope you dont mind if i walk in circles a few times and make myself at home

so this is the new grow!

the t5's are a new addition i think and are good choice for veg/cloning lights
so far the seedlings look like...seedling :)
off to a good start

sounds like you have some nice goals laid out for yourself
i def agree that cloning is the next step in your journey and you hvae a good light for it in that 200w t5

ive grown larryOG in the past and she is a knock out
heavy stone and nice buds
never grown out the GSC, so im very interested in how she comes along
once thing i like to do when growing multiple strains, is i use the colored electrician tape and make these little markers/ flags
(right now im using sections of chop sticks we got from take out)
i cut the chop stick ( or any thin wooden dowel) into small 3-4" sections, then i wrap a piece of colored tape around the end of each one

this gives me a quick visual marker to know which plant is which
plus they are easy to reuse and virtually free

really hope you have the success you enjoyed in the past and cant wait to see where this little adventure takes us!

/i dident forget about saying i would be posting some mountain bike pics too
oh and my mom said she might have this old meat grinder that i could have!
if thats not enough, the mrs just made some brownies!

im going to fire up a fat J and lets get this party started!

/plenty to go around and i hope others goin in the fun as well!
Good morning pop_rocks.
Thanks for comming over and defenatly make yourself at home.
New grow is off to a slow start, I forgot how slow they are the first couple weeks.
The new light should be good. Last time I was under 600w mh from seedling and I had they light like 30" above them at this point. I have them about 6" under the t5's and will let them get a little closer as they grow.
I hope to learn a lot on this one and defenatly need to make clones because I'm almost out of seeds. I want to try new strains but can't ever decide which to get when I'm checking them out online. I have 3 more Larry, 1 GSC, and 2 Blackwater left. I plan on growing nonstop for a while and if I get it timed right I'll pull a harvest every 9-10 weeks. Looking forward to seeing how these plants will differ from my last. Glad to here that Larry is good, people have complained about the GSC from cc but others say that there are grate pheno's to be found even a minty one. I don't think I've ever had minty weed before.
I've got some wooden skewers that I was using to prop up seedlings last time that would work great as markers.
I'm stoked to have plants to care for again and hope these girls do well. It's defenatly going to be an adventure.

I'd love to see some mountain bike pics and I hope you get the grinder. Speaking of food again I just found the Munchie Mansion threads on icmag. Seems we're not the only ones that have a love of good food. Some of the pics on the food porn thread are killer. Some very talented chefs here and I plan on starting or at least contributing to a food thread here. I plan on sharing my experience on bbq, sausage making and even post on cheese making a bit. I'll have to start taking more pics of food and sharing as well.
Thanks for making your way over to this new chapter in my education and enjoy those brownies.
 

Fiddynut

Active member
Hey Fiddynut, glad to see you starting another thread. Great summary on what you've been doing and what you're looking at exploring in the future. Sounds like you learn through experience in the same way I do.

I'll be excited to see what your end result looks like with these OGs. If you do top or train them, you'll see a huge increase in your yield. Give them the right conditions and love and they'll definitely take advantage of it.

I'll be subbed to follow along, Good luck!
Good morning GastroGrower.
Thanks for checking out my new grow. My first grow was fun and I learned a lot. As you said some of us learn through experience and I've always felt like that is accurate for me. Last grow was just about getting general experience and showing myself I can grow out a plant. This time I want to learn more about feeding my plants, cloning and training. I'm going to love them and do my best to keep them happy.
Thanks for the encouragement and following along on this grow.
 

Fiddynut

Active member
Quick update

Quick update

Just a quick update I watered this morning and the baby's look good. It has been a week since I soaked the soil in preparation for the seeds so I think I had the soil on the wet side. I guess that's it for the update not much to do just watch them grow....slowly.

So I found a foodie thread on icmag called "food porn". Food and cannabis are some of my passions in life. I made a couple food posts and plan on taking more pics of my food in the future. I will be posting pics and some recipes in the future. I found some pics on my phone so I posted them, if you are interested in what I'm eating and cooking check it out. Anyone else like great food? Let's get that thread rocking and there are some great cooks here on icmag.
 

pop_rocks

In my empire of dirt
yeah seed is slow at first and then it grows like mad
lets hope for the best tho and then get you started wiht clones
then you can put those last few beans in the vault for a rainy day while still having grade A smoke growing
/i had ot learn the hard way that you cant rely solely on clones all the time and now have a few beans stashed away

plus lets hope for some good phenos in this next run
a minty weed would be awsome to have growing
when i was younger i smoked this oaxacan weed that was super minty, like smoking a kools cigarette almost
you could take these huge rips because the mintyness kind of cooled the smoke

for the time being get your supplies together and once they have a few solid nodes worth of growth you can start taking cuts
i def believe you can pull off several crops over the winter
by the time these seedlings are finished wiht flower, you should have a bunch of rooted clones ready to move in

damn son, that is some legit meat you have in the other thread!
thanks for pointing me in the right direction
i will have to download the pics from my phone when i get a chance
/this year my mom gave me a ribeye roast for my birthday
my mom is oging on a trip later in the month so im oging to try and get to her and see if we can dig up the meat grinder before she goes

im glad gastrogrower is on board for the adventure and would like to hear his comments as we go along
/same for anyone lurking, give a holla and say hi

looking fore ward to another great grow!
 

GastroGrower

Active member
I can second Pop_Rocks' comment about working with both clones and seeds. Its nice to be able to continually dial in a strain by working with clones, and then exploring for new genetics slowly through popping seeds every now and then. Plus, we all know disasters happen, so it's great to have something as backup when you loose mother plants.
 

Fiddynut

Active member
yeah seed is slow at first and then it grows like mad
lets hope for the best tho and then get you started wiht clones
then you can put those last few beans in the vault for a rainy day while still having grade A smoke growing
/i had ot learn the hard way that you cant rely solely on clones all the time and now have a few beans stashed away

plus lets hope for some good phenos in this next run
a minty weed would be awsome to have growing
when i was younger i smoked this oaxacan weed that was super minty, like smoking a kools cigarette almost
you could take these huge rips because the mintyness kind of cooled the smoke

for the time being get your supplies together and once they have a few solid nodes worth of growth you can start taking cuts
i def believe you can pull off several crops over the winter
by the time these seedlings are finished wiht flower, you should have a bunch of rooted clones ready to move in

damn son, that is some legit meat you have in the other thread!
thanks for pointing me in the right direction
i will have to download the pics from my phone when i get a chance
/this year my mom gave me a ribeye roast for my birthday
my mom is oging on a trip later in the month so im oging to try and get to her and see if we can dig up the meat grinder before she goes

im glad gastrogrower is on board for the adventure and would like to hear his comments as we go along
/same for anyone lurking, give a holla and say hi

looking fore ward to another great grow!
Good morning pop_rocks.
I'm sure these girls will be cruising in a couple weeks or so once they get some solar panels and start sucking up some light. Since I don't have anything in the flower tent I may give them a couple weeks of the 600w mh light to hurry them along a bit. I will wait at least a couple more weeks to do this.
I am really looking forward to making clones. I guess it will take some work to get the timing right so they are ready for the flower tent when it is ready for them. I'll just have to try it and get some real world practice.
I do want to try some new genetics but every time I go on the seed bank web sights I get overwhelmed by all the varieties. All the pictures look killer but it's probably best to do some research on the strain and breeder. It's something I'll be doing soon. I'd like to try a new strain at least every couple grows to get variety.
A minty weed like kool cig's. I use to smoke kool and newports back in the day so that would be interesting. I guess we will see what pheno's pop up this time.
I'm going to hit up the grow shop this week and get the dome, rooting gel, and plugs and I should be ready to go. I'm also going to get some of those yellow sticky cards in case I get any more of thous flying bugs.

I'm loving the food porn thread! All kinds of great food from all over the world. I usually don't take pictures of my food but that is going to change. I can't wait to do my next run of sausage, I'm going to take a bunch of pics and document it. I'll be taking more pics of other dishes I do as well. I'll try to include recipes but to be honest I only use recipes for a few of the things I make. Most of the things I cook by memory and it's not exactly the same twice.
The ribeye is one of my favorite pieces of beef. Roast or stakes it is so rich and buttery. Even slice thin and made into a cheese steak sandwich it's superb. I like to roast them low and slow at like 200 deg and sear them at the end. I do them in the oven or over charcoal on smoker but with out wood so it doesn't get too smoky just a little charcoal flavor. I rarely put anything but salt and pepper on them since they are so flavorful.
Do you have bratwurst in San D? I just take it for granted since there is so much German food where I live. Get that grinder and you will be able to make something that you and your friends may not have tasted before. Even if you have had brats there are many styles and these may be new to you.
 

Fiddynut

Active member
I can second Pop_Rocks' comment about working with both clones and seeds. Its nice to be able to continually dial in a strain by working with clones, and then exploring for new genetics slowly through popping seeds every now and then. Plus, we all know disasters happen, so it's great to have something as backup when you loose mother plants.
Good morning GG.
I'm looking forward to regrowing and dialing in some of my favorite strains and exploring new ones. I have to find some faves first though. Like you said disasters happen and as likely since I'm so inexperienced.
I see you work with some autos and I may be interested in trying some sometime. I'm thinking that if there's some extra room in the veg tent I'd like to try one or two and get some more variety that way. I will have to wait a little while for that tho since I think I'll have my hands full for a bit learning to clone and train what I have now.
 

pop_rocks

In my empire of dirt
first we are going to get your cloning technique down so you can take consistent, healthy cuts
depending on how you want to grow, you can flower numerous smaller plants or fewer larger plants so timing is something that is easier to adjust
what size container did you use the last time?
you could always cut that size in half (or more) and flower twice the number and still come away with as much if not more
/maybe it would be a good exercise for you to try one day just to do, we can talk bout that later

i would hold off on moving the plants into the 600w tent for a bit
right now they are more limited by the size of their roots than anything else
once they grow a larger root mass then they can handle more light

yeah i totally know what you mean about bringing in new strains to mix things up a bit
lets see how you like the larry and gsc first
you can always throw down those two blackwater seeds if you want as well
that will give you three strains growing at once
i would not try growing too many different strains until you have dialed in your grow and gotten to know the plants a bit better
its better to do a few things really well than take on too much and get overwhelmed
plus, lets see how these babies turn out
/talked to a friend and he confirmed the minty cookie

rib eyes are the king of the cow man
i like a good porterhouse too, but rib eye is something special
ill talk to my mom soon and see about the grinder
makeing mrauts sounds rad
we have a good german market/ restaurant near where i work but i would rather make my own
 

Tri_Cho_Me

Member
hey hey buddy!
hope you dont mind if i walk in circles a few times and make myself at home

:laughing: I'm dying!


Congrats Fiddynut! Looks like you're off to a good start with your second grow. Can't wait to see your thumb get greener. I am heading in the organic/no-till direction myself.

Good luck!
Tri_Cho_Me
 

Fiddynut

Active member
first we are going to get your cloning technique down so you can take consistent, healthy cuts
depending on how you want to grow, you can flower numerous smaller plants or fewer larger plants so timing is something that is easier to adjust
what size container did you use the last time?
you could always cut that size in half (or more) and flower twice the number and still come away with as much if not more
/maybe it would be a good exercise for you to try one day just to do, we can talk bout that later

i would hold off on moving the plants into the 600w tent for a bit
right now they are more limited by the size of their roots than anything else
once they grow a larger root mass then they can handle more light

yeah i totally know what you mean about bringing in new strains to mix things up a bit
lets see how you like the larry and gsc first
you can always throw down those two blackwater seeds if you want as well
that will give you three strains growing at once
i would not try growing too many different strains until you have dialed in your grow and gotten to know the plants a bit better
its better to do a few things really well than take on too much and get overwhelmed
plus, lets see how these babies turn out
/talked to a friend and he confirmed the minty cookie

rib eyes are the king of the cow man
i like a good porterhouse too, but rib eye is something special
ill talk to my mom soon and see about the grinder
makeing mrauts sounds rad
we have a good german market/ restaurant near where i work but i would rather make my own
Good afternoon pop_rocks.
I've herd of people growing a bunch of small plants I think called sea of green. Once I get the hang of taking cuttings I think I'd be down to try it. If growing from seed it could get expensive to pop 15 or 20 seeds for that.
The last grow finished in 14" round pots. A 5 gal bucket fits into these pots and is slightly taller than the pot but the pot is wider at the top so I'm guessing they hold at least 5 gal of soil. I have some 10" and 12" pots that I was trying to grow tomatoes and peppers in last summer. I was planing on 3 plants just like last time. I was originally going to grow 4 last time but had one male and was left with 3 and in hindsight it would have been pretty crowded in there with 4. I also want to add a tower fan in one corner of tent and would have had plenty of space with 3.
Will hold off on moving them to the 600 for a while but was thinking that since I had the space available on this one I could cut the time down with more light once I take cuttings and they are big enough to handle it.
So far I haven't seen the GSC sprout so I'll give it a couple more days. If I don't get another seedling soon I'm worried that the 2 I have will be too far ahead and that will complicate things. If I was confident I could successfully clone I'd be more inclined to pop more than I need and just keep them as mothers and grow them out on the next run. As it is I may have to pop a couple more and hope for the best.
I like your philosophy of doing a few well and not getting overwhelmed. I still have so much to learn and a lot of confidence to gain that I could easily become overwhelmed. Nice to hear that there is a minty pheno and cc describes these as thin mint.

I love a good porterhouse too. Something about the fat right up against the bone that is so succulent. Plus getting a tenderloin and a ny strip in one steak is boss.
 

Fiddynut

Active member
:laughing: I'm dying!


Congrats Fiddynut! Looks like you're off to a good start with your second grow. Can't wait to see your thumb get greener. I am heading in the organic/no-till direction myself.

Good luck!
Tri_Cho_Me
Thanks Tri_Cho_Me. The baby's are small and growing slowly at this point. I can't wait until they take off in a few weeks. I hope my thumb gets greener too. Looking forward to seeing your updates and how your girls are doing.
 

Fiddynut

Active member
Quick update

Quick update

Just a quick update tonight. The baby's were thirsty tonight so a little water for them. I pH'd the water with a very little bit of earth juice. Since I'm not using the earth juice as a nute on this grow at least I can use it to lower my pH. This bottle is so acidic it seems like it's as good as pH down and takes very little to get my water to low to mid 6's. My two Larry's are looking good. I'm trying to sprout a third seed but it has not popped up yet. Kind of boring so far and not much to do but watch them until they need water next time.
 

pop_rocks

In my empire of dirt
yes, its called sea of green!
one of the first indoor grows i ever saw that impressed me was tihs sweet carpet of 18" tall plants, each one like a bottle brush of bud
no side branching just fat tops
you would want to use the samller pot so you can pack them in tihgter and we would hvae to figure out a watering scheme that would work for you
/maybe something automated with drip lines, but that is for a later conversation

first we want to get your plants happy and growing so we can see what is what
ill keep my fingers crossed for your gsc, but sometimes seed just dosent pop
we could always work with the larry tho
what we want is to start taking some cuts and then figure out which will be the best

you nailed it wiht the fat next to the bone comment!
not only does the bone add something to the meat but my dog will sit on the porch for an hour gnawing on them
its like getting a treat for both of us!
 

Fiddynut

Active member
yes, its called sea of green!
one of the first indoor grows i ever saw that impressed me was tihs sweet carpet of 18" tall plants, each one like a bottle brush of bud
no side branching just fat tops
you would want to use the samller pot so you can pack them in tihgter and we would hvae to figure out a watering scheme that would work for you
/maybe something automated with drip lines, but that is for a later conversation

first we want to get your plants happy and growing so we can see what is what
ill keep my fingers crossed for your gsc, but sometimes seed just dosent pop
we could always work with the larry tho
what we want is to start taking some cuts and then figure out which will be the best

you nailed it wiht the fat next to the bone comment!
not only does the bone add something to the meat but my dog will sit on the porch for an hour gnawing on them
its like getting a treat for both of us!
Good morning pop_rocks.
I'd be down to try sea of green sometime for sure. I would bet it works best with cuttings from the same plant so they grow the same hight and you can get the canopy even and keep it that way as they grow.

I think my plants are looking good and I'm pretty sure my GSC sprout is going to make it. I'll tell more about plant status in an update next.

I've been reading about VPD in a few threads on icmag. Not sure if you believe in the charts or not but I have a very low humidity for the temps I'm at. I'm pretty sure that trying to get my humidity up into the 70% range would be bad in my environment. I guess that I'm reading that optimal VPD increases the growth rate but I'm not sure how it affects stress and health of plants. I don't want mold so I keep humidity low and that seemed to work out last time. Maybe I'll dial up me dehuey up 5% and see what that does for me. I'll have to read a bit more before I make any big changes. With the change of season my temps are around 69 deg lights off and 73 deg lights on.

I'll be going to the hydro shop this weekend and getting a humidity dome, some rooter plugs, and rooting gel. I also will get superthrive since I've herd such good things about that stuff. I'm also thinking about getting mykos because I'm hearing that it is very beneficial for roots. I also need sticky cards in case I get any bugs again that should trap,one so I can get a close look at them and decide on the best way to deal with them.

That's great that you share your steak bone with your furry friend. I bet she loves that special treat. I made a nice ny strip steak for dinner last night with a giant potato and some nice locally grown veggies. Simple and delicious. I couldn't help but post it in the food porn thread.
 

Fiddynut

Active member
Update and pics

Update and pics

Time for an update and the baby's are looking good. I'm not sure if it was the earth juice or what but they have been growing a bunch and doubled in width in the last 2 days. The ej shouldn't be too strong for them with an npk of 2-1-1. I used 1/16 tsp in 3 cups water so I'm keeping it light for the 10 day old seedlings. I'll probably use it the next couple waterings but soon I'll have to start using the synthetic stuff to get them use to it. Still not sure what dosage to give them but I'll start with 1/2 or 1/4 recommended dose and work up from there.

Good news for my GSC sprout as well. It's up and the stem looks thick and healthy. It hadn't shed it's hull yet as of this morning but I'm sure it will soon. It will be interesting to see if it catches up with the 2 Larry OG seedlings that are about 6 or 7 days ahead of it. I may top the Larry's twice and the GSC only once if it still needs to catch up towards the end of veg.

On my to do list is to get to grow shop and get cloning supplies, superthrive, makos, and sticky traps. I also want to read more about VPD and plant health. Other than that not much to do but watch these baby's grow and give them love.

Here are a couple pics.
 

pop_rocks

In my empire of dirt
could you discribe this vpd to me?
/...i.... am...... feeling....very......lazy

its not an acronym im familiar wiht
its weird that you mention humidiyt, because once you mentioned being concerned about your RH getting into the 60s and because of where i live 60-70% rh is normal

yes, spot on about why you would want to use clones in a sea of green
not only do you get unform growth but you are growing the most potent example of the strain you are running

its also easier to trim because you dont really have much larf to mull over
you just take the top x" of plant and the rest goes to the hash pile

sorry if im missing something here but which pic is of the new gsc seedling?
 

Fiddynut

Active member
could you discribe this vpd to me?
/...i.... am...... feeling....very......lazy

its not an acronym im familiar wiht
its weird that you mention humidiyt, because once you mentioned being concerned about your RH getting into the 60s and because of where i live 60-70% rh is normal

yes, spot on about why you would want to use clones in a sea of green
not only do you get unform growth but you are growing the most potent example of the strain you are running

its also easier to trim because you dont really have much larf to mull over
you just take the top x" of plant and the rest goes to the hash pile

sorry if im missing something here but which pic is of the new gsc seedling?
Vapour 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. Once air becomes saturated water will condense out to form clouds, dew or films of water over leaves. It is this last instance that makes VPD important for greenhouse regulation. If a film of water forms on a plant leaf it becomes far more susceptible to rot. On the other hand, as the VPD increases the plant needs to draw more water from its roots. In the case of cuttings, the plant may dry out and die. For this reason the ideal range for VPD in a greenhouse is from 0.45 kPa to 1.25 kPa, ideally sitting at around 0.85 kPa. As a general rule, most plants grow well at VPDs of between 0.8 and 0.95 kPa [1] - copied from Wikipedia.

Originally Posted by Kcar
Here is a simpler explanation

Humidity and Vapour Pressure Deficit (VPD)

For years Relative Humidity (RH) has been used as a measure of how much water vapour is present in the air and is probably still the preferred method used by experienced growers. In a greenhouse, the amount of water vapour present has a direct effect on a plants ability to transpire and hence grow.

Another measure called vapour pressure deficit (VPD) is also used to indicate humidity and is felt to be more directly related to a plants wellbeing. VPD combines the effects of both humidity AND temperature into one value and so gives a good indication of plant wellbeing without the need for the grower to do any mental arithmetic. VPD values run in the opposite way to RH values so when RH is high VPD is low.

If humidity is too low (i.e. high VPD), the stomata on the leaves tend to close in order to limit transpiration and prevent wilting. This closing of the stomata will also limit the rate of CO2 uptake and hence limit photosynthesis and consequently plant growth. Low humidity also reduces turgidity (water pressure within the plant cells) and this in turn also restricts growth. Blossom end rot in tomatoes and capsicum can also be attributed to low humidity (high VPD).

Conversely, if humidity is too high (i.e. low VPD) the stomata will fully open but even so the plants will be unable to evaporate enough water to carry minerals into the plant and so again, growth will be impeded and mineral deficiencies (particularly calcium) may occur. In addition, the plants may exhibit soft growth, fungal problems and mineral deficiency symptoms.

It is frequently stated that VPD more closely matches what the plant "feels" in relation to temperature and humidity and therefore forms a better basis for environment control. Unfortunately, VPD is extremely difficult to determine accurately as it is necessary to know the leaf tissue temperature. Attempts to measure leaf temperature reliably on an ongoing basis have often ended in disaster. One of the problems is that the plants leaves are in differing amounts of sun with some leaves in full sun, some in partial sun and others in full shade. This makes the concept of "leaf tissue temperature" particularly complex.

By measuring the temperature and relative humidity within the crop canopy the calculated VPD is still a useful measure as it combines both temperature and humidity into a single measure in a way that approximates the well-being of the crop. As an example, for many crops it is suggested that RH should be kept between the following limits at the stated temperatures:-


Temperature oC Min RH (apply fogging) Ideal RH Max RH (for disease prevention)
15 - 50 73
20 46 64 80
25 60 73 86
30 70 80 89

You can see from the table that the higher the temperature is the more humidity is required by the plants. The above makes it difficult to specify control parameters as different RH settings are required at different temperatures.

Now look how much simpler this is made by using VPD as the whole of the above table is contained in just three VPD values as follows
Maximum VPD (too hot and dry - apply fogging) VPD ideal

VPD too low (too cool and humid -warm/ dehumidify)
1.25 0.85 0.45

AutoVent 2 and 3 environment controllers estimate the VPD based on the air temperature and humidity in the crop canopy. It will only be close to the true figure for a healthy transpiring crop. The VPD calculator below allows the VPD to be estimated based on both air and leaf temperatures. This clearly shows the possible error in VPD due to just a 1 deg C difference between air and leaf temperature.

As a general rule, most plants grow well at VPDs of between 0.8 to 0.95 KPa

Fogging or other humdification is usually applied at VPDs above 1.25KPa and heating and dehumidification at VPDs below 0.45KPa

The above is from a thread on icmag - https://www.icmag.com/ic/showthread.php?threadid=331510

There are quite a few threads on icmag about this and many growers swear by it. At the same time I've herd that it works well on the west coast but not as well in the Midwest whare there is more mold spores floating around. Some say you need to seal the room up and use hepa filters to get humidity this high without mould issue. I grow in the basement of a 60 year old house and creating a sealed room with filtered air is not really an option.

So I'm wondering if ideal VPD is just a way to optimize growth or if it has a general effect on plant health and if I should try to get my humidity up a bit. I don't want to make big changes over last grow because I'd hate to loose a whole harvest to mold or something. I'm sure if I keep reading the answers will be their.

The GSC seedling is nearly visible in the group photo but here is a better one.
 
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