The Home Stretch: Rh / Temp Control, LEDs, Sub-Irrigation in "Tents"

Shout out to the micro forum, coco forum, sub-irrigators, there's a lot of good stuff in there. Also, The Potcast. And lots of others.

I have some back logs of photos and observations on growing errors I've made. Hopefully this can help somebody debug their grow

Very few of these observations will be original. Thanks to everyone who has grown before.

In my model, there are some basic categories of error:


And things to consider with each of these are


And the objectives that we are seeking to affect are


Something that DJ Short says is that it's about the final effect of the medicine. Tea (camillia sinensis) cultivators produce a broad range of flavors and effects from the same plant based on differing growth conditions and physical processing. Whether leaves are shredded finely for black tea, rolled into balls or spears for oolong tea, left to dry undamaged, grown out into broad leaves or picked early as small buds, the shape of the plant at harvest determines some initial chemical conditions and the shape during oxidation and storage determines, among other things, surface area to volume ratios which affect the short and long term evolution of the chemical conditions in the final product.

Similarly, bud density on the plant affects trichome quantity and development. Super dense buds that don't have room for proper trichome development will crush the glands more readily even during growth, changing the profile at harvest as well as the curing dynamics.

Increasing total bud mass might push buds in one habit or structure into the super dense regime, but not others.

Increasing total resin content might disproportionately increase one terp over another, which might be undesirable. Perhaps increasing total resin by one mechanism simply adds limonene or pinene, masking a rare flavor in a strain. Terp ratios change the effect of the herb. Some herb may paradoxically become trippier if its resin contents is decreased.

Different terps evaporate at different rates, and spectrum probably affects expression. This means that different lights and atmospheric conditions will change these ratios. And perhaps most critically, drying and curing. It is said time and again, preservation is one of the most crucial stages because during the course of 2 weeks of drying and curing you are risking months of bud growth and resin development in order to purge water from your buds so that they will keep safely.

Every decision you make during preservation processes has a larger effect per unit time than decisions made during growing, and so I make sure to check on my drying and curing buds about four times as often as my drying buds. It takes a lot of time to grow resin, but you can lose it in a jiffy.

This thread is all about avoiding errors and manipulating our four flower objectives in order to achieve a desired ultimate effect.

Current Grow

Current Grow

I thought it would be good to start with a pic from my current grow before I show some of the old stuff.

This is at the end of the third week since switching from 18/6 to 12/12.







A few rounds ago I ran an open pollination with seven sativa fathers (notated "AllSat") and a bunch of mothers. The sativa fathers included El Dorado, Royal Flush, and Urban Poison. There were a few ladies in the tent at the time. One was Flo, and another was a very neutral odor, middle of the road but strong bag seed from a strain I dubbed Eclipse since I sprouted it during the '17 North American solar eclipse.

These plants are Flo x AllSat and Eclipse x AllSat. Anything AllSat streteches pretty hard, I've found. I wanted to put some more Central American genes into the Flo with the El Dorado and Royal Flush, but also wanted to see if the African landrace from the Durban -> Urban would bring something new to the table. So these 11 sativas could have some interesting variety.

Lights are blurple Chinese LEDs from 2012, about 195 Watts measured at the wall. Supplementing are 2 of GrowMaus' far red initiator pucks, which I run for 30 minutes at lights off (10 minutes before till 20 after, but my timers are analog so who knows, I better check to make sure the mains and the supps are synched).

Running 3 Earthbox Jr.s with the included soil. I have built sub-irrigation systems before and thought I'd give this a shot. The soil runs pretty damp for my taste and I do not keep the res wet in general. I'll be amending with biochar and maybe some volcanics for heavy aeration next run (I will only spring for this if I really go "living" and recycle permanently). Nonetheless they are nifty little rigs.

Current Grow: Spring 2019 (pg. 1/2)

Current Grow: Spring 2019 (pg. 1/2)

I'm going to be jumping back and forth a little in time so I'll try to title each post according to which grow it addresses.

I wanted to talk a little more about my setup now before I turn back the clock.

Here's the control center.

The humidistat is controlling a small CVS cool mist ultrasonic humidifier. The top of the humidifier fits nicely into 6" ducting which is the air intake of my tent.




Some holes in the first foot of ducting allow air to be taken in, since the humidifier blocks the duct's own opening. You can add a few more than you need and then tune which ones are open by sliding more down over the humidifier to block them, or collapsing or opening the accordion corrugation. Mine are really in the first 6" since I don't use much air flow for the most part; just enough for gas exchange. Evaporation in the lung drops the intake temperature down and partially cancels the heat contribution from the light, negating the need for a high air flow to keep the temps down. If it is still too hot you can open the duct port at the top of the tent on the side opposite the exhaust. This allows air to flow in, over the lights, and out the exhaust, without touching the plants or busting up their humidity bubble. The right balance must be struck so that sufficient air still flows over the plants. Fortunately, if you are blowing mist through your intake, visualizing airflow is trivial. An open top flap works totally fine if you are not trying to flip the temps at light. I have found that leaving the top flap open after day cooling reduces the intake at the lung
in heating configuration sufficiently that I cannot heat the tent at night without closing the top flap. Less hassle than re-configuring the lung, to be sure, just don't forget.

The corrugation catches condensation and acts as a buffer, smoothing the more direct action of the humidifier. If the humidifier is turned off, the intake air passing over the damp corrugation will keep the intake air within a couple of points of the target until the dew is depleted. The buffering power of the lung is strong. If flow conditions change suddenly so that air spends more time in the lung than it did moments ago while depositing moisture, it will cause the humidity to spike and sometimes overshoot the target even while the humidifier is off. A decent lung length can control the humidity in the tent decently well even without a circulating fan on the inside, and coupled with a circulating fan, 3 feet of 6 inch lung are enough to strongly control the humidity in a tent with a small CVS cool mist humidifier, provided the air flow is tuned appropriately. You need to maintain negative pressure on the tent and the majority of the air needs to come through the lung. I have placed 8 cheap temp / Rh gauges at the bottom of my tent and tracked down air leaks according to which gauge read low. Those hose ports with the draw strings need to be pulled tight, cord looped around the aperture and pulled tight. Otherwise, one seedling can get a blast of dry air from a jet. Albeit a small effect.




The opposite top corner of the tent exhausts through 6" ducting to my fan and scrubber. The probe for the humidistat is at the exhaust of a little case fan I ducted. During early veg things were set up so that the fan induced a circular flow around the earth boxes, sucking in the undissolved mist and incorporating it by the time it left the duct. This avoids condensation on the probe and leads to more stable behavior.





This kept the humidity fairly well mixed. In late veg, the plants are creating their own environment and the mixing down there matters less. Sometimes rearrangements block the circular flow but it's still a good place to measure.

Current Grow: Spring 2019 (pg. 2/2)

Current Grow: Spring 2019 (pg. 2/2)

The thermostat immediately next to the humidistat controls the lights. The probe is placed at the height of the lights on the side furthest from the exhaust, theoretically the hottest part of the tent. The light timers are plugged into the thermostat so that the controller tries to heat the tent with the lights until the temperature is 90 F. If my tent reaches 90 F at the height of the lights there is a problem, and I want my lights off so I don't boil off terps. Maybe my AC shut off (this has saved me more than once), or maybe something obstructed my intake. A temperature of 90 F at the lights results in a canopy temperature of about 86, which is far from fatal even near the end of flower. In late flower I step this threshold down so that my late buds never see anything hotter than 82 or 80. I am of the belief that the more I can smell my plants, the more terps I am losing. This has to be balanced with transpiration and stress response, though, so it is not as simple as "make it cold".

The leftmost thermostat measures temperature after the bottom mixing fan. I use this to heat my tent at night for an inverted day / night delta. There is evidence that warmer nights and cooler days reduce stretch compared to cool nights and warm days. My AC keeps my days cool, but without the lights, my nights are cool too. This thermostat controls an oil heater, to which I route my 6" intake at night. Since it is a pain and doing it safely is a bit of a hassle and a space hog, I only do this when stretch avoidance is critical. The thermostat plugs into a timer so that this only runs at night. I want to take a moment to stress that I chose an oil heater both for safety and because it buffers the heating effect like the lung does. I was able to keep my grow room around 77 with no AC running while the inside of the tent was around 82. This was possible because the oil heater stayed hot enough for long enough after shutting down that it didn't need to stay on for much of the time, i.e. its duty cycle was low, and thus didn't actually heat the room that much. Note the aluminum hood over the intake to guide warm air from the vanes. It is even more critical for heating than for humidifying that the intake be exclusively through the lung.

Now is a good time to mention that the lung length should be as short as possible to avoid losing heat on the way to the tent. I had to shorten my lung to achieve this, but even un-insulated it worked. You may consider insulating if you are having problems. Insulated duct exists, bubble wrap is a good way to add it. Similarly, when operating in humidifying mode, the lung drops the intake temperature a couple of points, which can be good or bad. It is fairly clear how to use a Y-adapter on the ducting to control both heat and humidity so that there is no need to switch the configuration at night, but I haven't summoned that level of commitment to the temperature inversion.

PLEASE note that it is extremely DANGEROUS to mess with heated intake air. An electric oil heater with nothing hanging above it or attached to it, essentially sitting in free space, in a room with no cats, is the only way I will do this. And it still feels wrong. No NiChrome heaters please.



Here's a shot of the far red initiators:



And I know I said I had blurple lights, but really they were some of the last generation of narrow band LED lights before the white CREE and COB lights started getting popular. There are a couple different blues and reds, a little green, and what are either IR or dead (but don't seem empty or UV) slots (the company did not provide UV as an option). Mine were on clearance so I took a gamble. They have never exhibited symptoms of spectral deficiency, so I think I got lucky with somebody's experiment.

Exhibit A: A Grow In Which I Learn About Humidity (pg. 1)

Exhibit A: A Grow In Which I Learn About Humidity (pg. 1)

I used to run hydro. I've run DWC, SWC, lots of drips ( hydroton rockwool perlite vermiculite coco ), and some SIPs. But everything always had, looking back, way too much water.

That included some pretty extreme conditions. I was growing in a computer case with 100 W of cool tubes and buds nearly touching the bulbs. It was way too hot and way too dry. No real symptoms other than the occasional bleached bud. Looking back it's odd.

Lately I've been growing largely in tents with soil substrate. And suddenly things change a little. Using even low to moderate wattage I start getting symptoms which first look like nute issues, but the soil is solid, and these symptoms are later revealed to be from transpirational stress.


Enter Vapor Pressure Deficit and humidity control. Problems solved. It's like I'm doing hydroponics again.


In terms of stability and, adding judicious foliar feeding, even growth speed, when I control humidity, my soil plants behave similarly to hydroponic plants in terms of healthy daily leaf shape and movement, and lacking long term health issues (heat stress symptoms mimicking deficiency) from heat stress, so that I can basically grow against my lights again, with bleaching again the limiting factor.


This grow will illustrate that principle.

Exhibit A: A Grow In Which I Learn About Humidity (pg. 2)

Exhibit A: A Grow In Which I Learn About Humidity (pg. 2)

This grow went down in an Ikea metal wire rack with foam core boarding around the sides and a mylar bubblewrap "door". This was a "Box" that evolved out of micro-cab principles scaled up a little, with a 6" exhaust to carbon filter at the top, and due to space constraints, a 6" intake at the bottom on the same side as the intake. Not that the whole thing was sealed too well, except the ceiling. I taped the ceiling up pretty well to the walls to make sure that the exhaust was pulling from an open-bottomed box of non-zero height, so that it can actually contact and thus purge the hot air bubble from the lights. But this only went down 4 inches or so, I didn't feel like using that much tape. Thus there were air leaks at every edge and corner. But that's not really the point.

This thing was functionally a small tent. But I was growing in a shelf of this wire rack while other hardware occupied the rest of the shelves, so my grow space was 18" from floor to light, so maybe 12" from soil top to the light bottom. Which is what I like, for some reason, because I grew up on micro. And maybe 3.5 feet long, 1.5 feet deep. There are measurements in photos somewhere we will run across.

This is really my little experiment Box. I can run small batches and test new conditions here. One time I ran an open pollination in here between Seven Sativa Fathers and, evidently, Eight Random Known Mothers, and hundreds of seeds from each mother.

I threw a bunch of seeds into 3 smart pots and surrounded them with 3 more smart pots for buffering and eventual lateral root expansion (smart pot walls are no obstacle for roots but serve as good partitions). All of this rested on a thick bed of perlite for drainage and wicked reservoir capacity.

Those are the 195 W LEDs on full blast overhead. You can already see the heat stress.

Exhibit A: A Grow In Which I Learn About Humidity (pg. 3)

Exhibit A: A Grow In Which I Learn About Humidity (pg. 3)

Yellowing and necrosis in young plants with plenty of water. But not enough humidity or airflow.

And the transpirational stress due to high heat and light but low humidity continues until the introduction of... The humidifier.

(This could have been "solved" by backing off the lights, but we don't have to)

The effect was instantaneous (an hour? Two?) in for leaf shape and texture (flatter and more tender is healthier than folded and tough), and the new leaves lacked yellow and necrosis when they filled in. Spreading of symptoms of already affected tissue halted to the degree that they can. Growth accelerated. Darker growth (aside from less yellowing).

Exhibit A: A Grow In Which I Learn About Humidity (pg. 4)

Exhibit A: A Grow In Which I Learn About Humidity (pg. 4)

Some more scrogging and some healthy growth.

I added a parchment sheet between the lights and the plants that serves as a "cloud" layer.

First, it directs humid air flow in a "U" shape first across the plants then up through folded triangle "dog-ear" flaps on the side opposite the intake, then back across the lights and through the exhaust in the ceiling. This keeps the canopy and the lights atmospherically separated in temperature and rh because the air is partitioned. There is largely laminar flow in the bottom layer and turbulent flow in the top layer because the several cooling fans in the lights really mix it up.

Second, the parchment is a diffuser for the light and scatters it. Point sources and LEDs create strong shadows. Arrays of LEDs mitigate this somewhat. This diffuser randomly scatters the light and so every point on the diffuser emits in all directions, so shadows are greatly reduced and coverage versus distance from the light source is increased. These are both important things for a micro grower. Of course I'm taking a hit in intensity but I am rich in light for this space and would gladly trade some of it for better characteristics (i.e. many angles of light reaching a broader area). In fact, with LED arrays, light density is no longer a problem, and light conditioning is the new frontier for pushing yield per volume.

You can note root expansion into the buffer pots (which were empty initially).

You can also note volunteer plants that sprouted in the buffer pots. I used these pots last round to create the seeds for this round and left them in extra long for high yield. Some of the early finishers fell to the ground before or during harvest and came up naturally a couple of weeks into this round, some from quite deep after watering and minor hassling while planting this round.

Images too large, passed up this thread. Looks good though...

Word

Word

Douglas.Curtis said:

Images too large, passed up this thread. Looks good though...

Click to expand...

Yeah, I figured somebody might say that. Thanks for the heads up. I remembered IC had bandwidth problems or didn't resize at some point, but the thread loaded instantly in my mobile device so I thought maybe it was fixed. Nonetheless, in case, at the beginning I tried the low overhead resize / compress method on imgur (the image host) but the basic ICmag links didn't work when redirected, so I postponed until there was a reason.

I'll look into it. Maybe check back in a month; the bandwidth might be less

EDIT: Looks like the attachment system will compress from an URL and accept the imgur "resized" URLs (which lack .jpg extension, which is why the normal embed wasn't working). I'll roll that out and link to hi res versions when interesting.

Exhibit A: A Grow In Which I Learn About Humidity (pg. 5)

Exhibit A: A Grow In Which I Learn About Humidity (pg. 5)

Once humidity was stable, growth proceeded healthily, not much to comment on. At some point I flipped to 12/12. Got a hermie! No surprise there. This box is not light tight.



You can see that the height from soil to lights is about a foot.

Thank you for fixing the images, and for posting this up. What you've been battling is transpiration rates.

When the plants are hot (above about 65-68F if I remember correctly), they use evaporative cooling to maintain a lower temp. To do this, they use water drawn from the root zone. The rate the plant uses water for cooling or hydration is what I'm referring to as the transpiration rate.

When the air is dry, the plants draw water up from the root zone. This water is used to keep the plant hydrated.

The general information is to keep your rooms hot and humid. This sets up a strong transpiration rate for cooling, and a steady draw of nutrients through the plant. Personally, I prefer very dry and cool conditions (though they're not great for soil, it wants 75Fish?) with the same transpiration rate. My plants have high transpiration to stay hydrated, they're quite cool at 68F.

I love what you're doing here, please keep us updated.

Exhibit A: A Grow In Which I Learn About Humidity (pg. 6)

Exhibit A: A Grow In Which I Learn About Humidity (pg. 6)

Since we saw the effect of humidity, here are the rest of the pics from this grow. I have the jar and scale shots. I think it was about 50g, which is like 0.25 g/W. I didn't veg for too long, probably less than 7 weeks from seed. Maybe as little as 5.

Flowering was probably 9 weeks, definitely less than 10. These sativas did not really "finish" in the sense that new flushes of flowers kept coming (probably stress) but there were plenty of mature calyxes.



Here are some links to some hi-res pics. Clicking stinks but maybe check out at least the labeled ones:

https://i.imgur.com/djQKCw2.jpg
https://i.imgur.com/SFrsWLI.jpg
https://i.imgur.com/cMqjZhb.jpg
https://i.imgur.com/J4z5aTi.jpg

Whole Grow:
https://i.imgur.com/jtGvkcI.jpg

https://i.imgur.com/P8jeROH.jpg
https://i.imgur.com/HJl47vB.jpg
https://i.imgur.com/19Cl68U.jpg
https://i.imgur.com/cQXEgqR.jpg
https://i.imgur.com/4bEId81.jpg
https://i.imgur.com/kO7N01S.jpg
https://i.imgur.com/pWE8KfD.jpg
https://i.imgur.com/plrLEMe.jpg

Cola Shot:
https://i.imgur.com/xYVGTYH.jpg

Addition: Probably worth noting that temperature swings were large since the cabinet was next to a drafty window in the winter. I got a lot of purple. Also the humidity stayed high until the end of the grow, so that accounts for the medium resin content. I believe if it had been lower there would have been more resin. I dried this stuff very fast because I was sparse on time (BIG MISTAKE); I lost a lot of the lightweight oils. Good stuff nonetheless.

Congrats!

Douglas.Curtis said:

Congrats!

Click to expand...

Thanks!

Douglas.Curtis said:

When the plants are hot (above about 65-68F if I remember correctly), they use evaporative cooling to maintain a lower temp. To do this, they use water drawn from the root zone. The rate the plant uses water for cooling or hydration is what I'm referring to as the transpiration rate.

When the air is dry, the plants draw water up from the root zone. This water is used to keep the plant hydrated.

The general information is to keep your rooms hot and humid. This sets up a strong transpiration rate for cooling, and a steady draw of nutrients through the plant. Personally, I prefer very dry and cool conditions (though they're not great for soil, it wants 75Fish?) with the same transpiration rate. My plants have high transpiration to stay hydrated, they're quite cool at 68F.

Click to expand...

Excellent, good to see we are at the same page. Rh, temp, and vapor pressure deficit.

Given a fixed transpiration rate, we can choose warmer or cooler. You run cooler (so do I) and I can see some reasons to do so. What is your motivation? Does it retain more terps, change growth habit? Definitely seems like cool temps high transpiration are the right thing for late flower since we don't need much growth and want to keep all the resin.

I think I know which grow I'll start posting next, but in the mean time, two questions I've been thinking about.

1.) What is the difference in bud quality between cool temp dry rh grown bud and warmer temp and damper rh grown bud, given that the two have the same VPD (vapor pressure deficit)?

2.) Say I grow 1 plant in a 2x2 ft space and yield 2 oz, versus 4 plants in the same space, same parameters (e.g. total soil volume, light distribution, etc.), same 2 oz yield. The single plant will have bigger colas (depending on cultivation style) and the 4 plants will have smaller albeit still decent length but narrower buds (closer to SOG style). What is the difference in bud quality between these two scenarios?

Whan I ask about "bud quality" I mean bud structure (or "habit", foxy with tons of tails vs. golf balls vs. christmas trees), oil / wax / terpene content (both flavor and light vs heavy weight molecules, light molecules lending that thin oily sticky feel that's easy to lose during dry and heavier ones that dense texture that persists through a rough dry and cure), and cannabinoid ratios.


I have my own observations on these topics but I'm curious to hear from other people first.

HyDroid said:

Whan I ask about "bud quality" I mean bud structure (or "habit", foxy with tons of tails vs. golf balls vs. christmas trees), oil / wax / terpene content (both flavor and light vs heavy weight molecules, light molecules lending that thin oily sticky feel that's easy to lose during dry and heavier ones that dense texture that persists through a rough dry and cure), and cannabinoid ratios.

Click to expand...

While we're at it, how about for fox-tail bud versus dense nugget bud? Has anyone noticed a pattern or trend in the high or the terps for the same strain grown fox-tail versus the same strain grown as dense golf balls?

Yes, transpiration is one key. As far as VPD goes, my values don't even show up on most charts because I'm usually shooting for 68F/20RH.

In my opinion, dry and cool produces/retains higher levels of terpenes with significantly lower levels of 'plant material.' Trichome dense cannabis. This also means your yield will be lower without a longer veg time. There is no explosion of growth during 'stretch.'

As far as 1 plant vs. 4 plants, as long as the environment is the same you're really looking at a difference in veg times.

Regulation Through Transpiration

Regulation Through Transpiration

Douglas.Curtis said:

I'm usually shooting for 68F/20RH.

Click to expand...

That's an admirable target.

Douglas.Curtis said:

In my opinion, dry and cool produces/retains higher levels of terpenes with significantly lower levels of 'plant material.'

Click to expand...

This makes sense from a moisture preservation perspective. Do you think lower temps cause the plant to retain additional terpene species it would normally lose and therefore alter the profile?

Douglas.Curtis said:

There is no explosion of growth during 'stretch.'

Click to expand...

I see, so

lower transpiration -> less water uptake and thus less nute uptake -> less photosynthesis and less cell division during 'stretch'?

So the general idea is to setup the environment to induce a target transpiration to control metabolism and therefore regulate growth?

Some terpenes begin vaping off around 70-72F I believe? It definitely helps with terpene retention. Downside is you have to keep everything below that temp while trimming, drying and storing.

I have high transpiration rates flowering cool/dry, and as a result the nutrient strength has to be low. The faster a plant uses water, the lower the nutrient level needs to be to prevent overfeeding.

I believe the difference is what my plants use the water to accomplish. In a hot/wet (tropical) environment, almost all plants grow MUCH larger than in other conditions. These plants are using water for cooling purposes, since they're already fully hydrated from the humidity.

With the arid (dry) environment, my belief is the plant structure forms more for preserving moisture. They need very little (if any) transpiration for staying cool. One idea I have centers around trichome density. When the plant emits water to evaporate, the denser the trichome layer is, the better the humid "micro climate" can be formed.

So, in my mind, the question about environment comes down to what your end product desires are. If your goal is pure harvest weight for sale, your best bet is to follow common Agricultural/Horticultural/Cash-Cropper advice. If your end goal is the most resinous, terpene-rich cannabis with the **least** amount of plant material underneath it, veg longer and flower cool and dry.

Both are high transpiration environments.