Outdoor Hydroponic Rooftop Grow - Recirculating DWC - No Airstones & No Medium!

Crazy Chester · Apr 24, 2020

Time for another rooftop grow.

This time, I'm doing medium-less, quasi-DWC hydro by re-circulating the nutrient solution from a reservoir near the ground by pumping it up to the one of three totes on the roof, which is connected to and gravity feeds to the one down slope from it, which connects to the last tote that finally drains into the reservoir below.

It was fairly easy and super simple to make the system. I used three of these to make the individual DWC planters:

5/8" (3/8" ID) hose like this:

Is connected to each tote with one of these:

And one (or more) of these:

Crazy Chester · Apr 24, 2020

Securely fastened with one of these:

My reservoir that the totes are fed by and drain to is one of these:

I'm using a water fountain pump I had laying around to pump the nutrient solution to the totes, like this one:

I also used some this:

Here's how it works from bottom to top and back again. First, the water is pumped from here:

Crazy Chester · Apr 24, 2020

Up one of these tubes:

Up the slope of the flat portion of the roof:

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To the tote at the highest elevation (all the way to the right in the photo):

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Crazy Chester · Apr 24, 2020

It goes in here:

And out here (where I have tape I can lift up to see the flow of the water - it's full of oxygen rich bubbles - like I like it!):

After she passes through the other two totes gravity fed in similar fashion, she drains out to a 90 degree bend, in which I stuck a 1/4" air vent (you can hear it sucking air in it as the water passes through:

And back into the reservoir:

Where it stays for a bit, as happy as can be, to collect some more oxygen before being pumped back up to the totes again. The pump runs 24/7. I've got about 40 gallons in the system, including 7.5 gallons in each tote.

Crazy Chester · Apr 24, 2020

This spot gets 10 to 12 hours of direct sunlight per day, every day, throughout the grow period until harvest.

And just who are the three lucky ladies who are to comprise this rooftop harem?

Meet, Super Lemon Haze ("Franco's Cut" via Purple City Genetics):

And Fire OG (Dark Heart Nursery):

Last, but hopefully not least, is Capstone (Capulator's Cut via Purple City Genetics):

WelderDan · Apr 24, 2020

Interesting. I grow DWC and I don't use a medium. I use a slice of pool noodle in place of a net pot. I'm curious how you plan on doing this without medium.

Crazy Chester · Apr 24, 2020

Hi WelderDan - thanks for stopping by. I guess it's not totally medium-less - the clones are in cubes that fit perfectly in 2" net-pots. So, I'm just going to cut a hole in the totes and pop 'em in there.

Edit: Actually, the Fire OG is not in a net-pot - she's just in a cube that's wedged into a hole in the cover of the little half gallon bonsai mom container I made. With her, I may just wedge her into the tote cover in similar fashion, or, perhaps I'll cut out part of the bottom of a net-pot, leaving the little circle at the bottom intact - then, I'll try to fish her mature root system through the hole at the bottom of the net-pot to get her cube to rest within the net-pot with her roots in the water.

In the future - when I have no more net pots and have an aero-type cloner set up, I'm going to do what you have done.

Heck, in my last indoor grow, I had two bare root plants in no medium whatsoever. I just made a hole in the cover, stuck them in and ran a string from the plants' lower trunk all the way up to an anchor at the top of the garden. It literally just hanged there - wasn't "planted" at all, but it worked just fine.

WelderDan · Apr 24, 2020

Crazy Chester said:
Hi WelderDan - thanks for stopping by. I guess it's not totally medium-less - the clones are in cubes that fit perfectly in 2" net-pots. So, I'm just going to cut a hole in the totes and pop 'em in there. In the future - when I have no more net pots and have an aero-type cloner set up, I'm going to do what you have done. Heck, in my last indoor grow, I had two bare root plants in no medium whatsoever. I just made a hole in the cover, stuck them in and ran a string from the plants' lower trunk all the way up to an anchor at the top of the garden. It literally just hanged there - wasn't "planted" at all - it worked just fine.

Well that certainly will work. I just let my plants sit on the bottom branches and that keeps them from slipping into the bucket. A few screws in the top lets me tie them off so they don't flop over, but your idea of suspending them will achieve the same effect.

My only concern is that you may have heat issues, but If you can keep the rez cool, then that should not be an issue. I will be watching to see how this goes. It's an interesting idea and I like that you are attempting this outdoors.

I might attempt something similar, but with my buckets buried in the ground.

It's a an outside the box idea and I dig it. I look forward to your results.

Good luck!

Crazy Chester · Apr 24, 2020

WelderDan said:
Well that certainly will work. I just let my plants sit on the bottom branches and that keeps them from slipping into the bucket.

Agreed.

WelderDan said:
A few screws in the top lets me tie them off so they don't flop over

I'm definitely going to do that too. These plants are going to have to be four feet tall - at most - but as wide as the roof gables will allow (so it's not in the faces of the neighbors). So, there's going to be a lot of training going on - I'm probably going to use string with sand bags to weigh them down the path I want them to mature into. It will also help protect them from the wind. I'm not far from the SF Bay - the wind is often quite robust up there (enough to sometimes rip old branches off Redwood trees).

WelderDan said:
My only concern is that you may have heat issues, but If you can keep the rez cool, then that should not be an issue.

You just hit on my number one concern as well. I've had this system running plain water for a few days now and have been monitoring the temperature. Talk about temperature swings! Today, at sunrise the reservoir was at at 60F, by noon it was 70F and by 3:30 it hit its high of the day - 82F!

I don't know if the plants will like that temperature swing, but I speculate that they may actually like it. In my DWC experience, plants grow like crazy when the reservoir temp is 75+ - it's merely high temp's effect on dissolved oxygen and pathogens that are of concern to me. If I were in a humid environment, I'd be scared of having to battle fungus gnats with higher res temps, but it's dry here. Also, I'm not too worried about other pathogens getting into the system because it's so sealed up - there's a taped up hole in the reservoir that I'm only going to open to add water and nutrients and there's the air vent - that's it.

Also, I read somewhere that the plants do their feeding at night. If so, there's plenty of dissolved oxygen in the nutrient solution overnight when the reservoir shows 60F temps. So, I'm leaning towards giving them a chance to try the water as is.

I'm curious what you think of my temperature swing - my half assed math indicates it is averaging around 70.66. I've found very little research on daytime/nightime optimal reservoir temp swings for hydroponics.

WelderDan said:
I will be watching to see how this goes. It's an interesting idea and I like that you are attempting this outdoors.

Cool - stick around - it'll be fun! I've pulled off coco medium hydro outdoors once - it was awesome! And - it was done without anyone attending it - I planted six inch clones and came back to five foot trees about to start the beginning of their flowering six weeks later (unfortunately, that grow is undocumented and is a story for another day).

WelderDan said:
I might attempt something similar, but with my buckets buried in the ground.

That's the smart thing to do and it's what I would have done, if I wasn't such a cheap bastard when I put this thing together. Heck, the only reason the table I built that holds the reservoir is at that particular height is that it worked with the pump I had available. Definitely - if you have a pump that can handle it, a buried reservoir will be the simplest, most economical way to keep the reservoir temps stable and at a low enough temp for the nutrient solution to hold gobbs of dissolved oxygen.

WelderDan said:
It's a an outside the box idea and I dig it. I look forward to your results.

Good luck!

Thanks!

WelderDan · Apr 24, 2020

If the rez is hitting 80+ your looking at root rot issue. Maybe wrap the rez in styrofoam

Crazy Chester · Apr 24, 2020

WelderDan said:
If the rez is hitting 80+ your looking at root rot issue. Maybe wrap the rez in styrofoam

Yes - I don't like that it gets over 80F, but, then again, it's only for maybe two hours during the day - then it starts its slow drop in temp from about 4 pm straight through the night and temps don't get that high again until the following afternoon, before dropping down again.

I'm definitely considering insulation, but at this point I don't know if that will trap heat into the nutrient solution. By insulating the reservoir, I fear it might lock the water into a tighter mid-70s hydro temp range - the greater period of time the plants would be in the pathogen friendly water may be risky.

Likewise, I'm not sure I want to lock the water temps into low 60's temps. But, if I were forced to choose, I suppose I would go for the low 60's - my indoor reservoir is in an un-insulated garage, but protected from direct sun - it ranges between 60 and 65 with the ambient temps. It seems to do fine with that indoors.

I'm thinking of doing a compromise method outdoors - insulating the planter totes on top of the roof while blocking direct sunlight from hitting the reservoir, but keeping the reservoir itself un-insulated.

The totes receive most of the sunlight, so they are probably most responsible for the nutrient solution increase in temps. The main cooling force I have is night-time ambient temps outdoors, so I don't want to prevent the reservoir from dissipating the heat of the day by insulating it.

Yeah - that's what I'm going to do - I think it will work to shave my high temp of the day down to around 75F. If that happens, my average nutrient solution temp will in the mid to high 60s and the few hours that it's outside the average temp range hopefully won't hurt the ladies.

Crazy Chester · Apr 24, 2020

As the sun was just about to reach over the fence and onto the cover of my reservoir, I put a makeshift awning over it - completely blocking the sunlight from directly shining on the reservoir. I'll keep it covered during the day and check my temps in the late afternoon, when, yesterday, it had reached 82F. Who knows - maybe I'll find out that's all I had to do to get a sweet outdoor hydro temp range the plants will love! If it helps, but not that much, I'll add the next step and insulate the grow totes on the roof.

Douglas.Curtis · Apr 24, 2020

DWC is a "Roots-In" type hydroponic system where the roots are constantly 'In' the nutrient solution. Solution temps are critical for success in DWC, with nutrient uptake issues below 65F and DO/Rot issues above 69F.

I strongly advise a slight re-design, to one which pumps that solution through clay pebbles or other media. The evaporation between waterings (you'll have to change to intermittent pumping) creates a swamp cooler effect in the root zone, effectively cooling the roots when temps reach the mid 80's.

Crazy Chester · Apr 25, 2020

Douglas.Curtis said:
I strongly advise a slight re-design, to one which pumps that solution through clay pebbles or other media. The evaporation between waterings (you'll have to change to intermittent pumping) creates a swamp cooler effect in the root zone, effectively cooling the roots when temps reach the mid 80's.

Wow - that's a really interesting solution - thanks! You really think the evaporative cooling effect would cool the roots that much?

Crazy Chester · Apr 25, 2020

In other news - my nutrient solution went up in temp today, rather than down - despite shielding of the reservoir from direct sunlight.

I'm either going to have to do the idea Douglas Curtis told me or I'm going to have to get a bigger pump, drop the reservoir into the ground and insulate the tote planters - either way, I just know it will be worth the effort!

Crazy Chester · Apr 25, 2020

After temps hit a high in the reservoir yesterday of 86F, it went right back down to ambient, around 56F before sunrise this morning. It was at 58F when I decided shortly thereafter to get to work.

Before I try Douglas Curtis' idea or WelderDan's idea of burying the reservoir (which I can do by purchasing just another 10 feet of tubing, since I found a long stashed pump that will provide the same flow despite the increased head), I thought I'd first monitor the reservoir today with a few changes from what I tried yesterday.

Yesterday, I blocked direct sunlight from hitting the reservoir by propping these up around it:

However that just made the temp in the res rise even more. I think it happened due to the black color attracting the sun and the tub shape provided a nice little bubble of trapped hot air right up against the res cover that heated it up nicely 2F beyond the temp it had reached the day prior when there was similar ambient temps to what it was yesterday.

So, today I covered the res with a heavy white cloth used for making roll down/roll up window blinds. It is big enough with enough overlap that it will block any direct sunlight from hitting the res and the white color should result in more of the sun being reflected, rather than collected.

Here's what that looks like:

I've been saving up bubble wrap bags that are made with bubble wrap that have reflective mylar on the outside and white on the inside. Rather than throwing them out in the trash, I used them to piece together insulated covers for the planter totes on the roof.

It now looks like this:

I will monitor it today to see if this comes close enough to fix the problem.

If not, I will extend the tubes, take out the table holding up the reservoir and bury it right below where the table used to be, leaving the totes on the roof with their insulated covers on (because I don't have hydroton right now).

If that doesn't work, I may go get a bunch of hydroton and try Douglas Curtis' evaporative cooling planter idea - or I may just scrap the idea altogether...

Douglas.Curtis · Apr 25, 2020

Crazy Chester said:
Wow - that's a really interesting solution - thanks! You really think the evaporative cooling effect would cool the roots that much?

Yes, it'll help out significantly with root zone temps. DWC or other constant contact with the nute solution requires temp control in that narrow window.

How much weight will the roof safely handle? I was going to suggest some type of PPK system (passive plant killer), but water is 8lbs/gallon. Much less weight with a drip-through type system.

Crazy Chester · Apr 26, 2020

Hi Douglas Curtis - thanks for stopping by again and for all your suggestions. I observed the res temps all day after making the changes I detailed above, and - with similar outside ambient temperatures as yesterday - I came in 10 degrees lower on my highest res temp!

Today, the high res temp was for no more than 2 hours at 76F. When I plot the rise (and fall) of the res temps over a 24 hour period, it is going from a low of 54F (roughly the two hours before sunrise) to a high of 76F (2 hours before sunset) at a steady rate of about 1 degree per hour. When I add all the average temps of each hour for the day and divide by 24, I get an average daily res temp of 65F. When looked at as an average, my temp is damn near perfect.

The problem is pretty much all the data that I've looked at that establishes an optimum root zone temp for cannabis (or tomatoes) assumes the temp of the res never changes from the temp tested. In other words - they don't take into account temperature range. So, there's really no data that I've seen that is applicable to what I'm trying to do. They all look at long periods of time at a steady res temp, rather than look at various res temps for only short periods of time within a range of temps or looking at average 24 hour temps resulting from various temps over a cyclic 24 hour temperature range.

With my new changes lopping 10F off my top res temp, I think I'm going to give the system a shot pretty much as is - as an experiment to do the study I wish I had the benefit of.

I'm also probably going to screw white covers over the current covers of the planter totes - it should have a brim on a hat type of effect - if I keep the direct sun off the asphalt roof that borders the base of the totes I should be able to lop another degree or two off the top of temp range.

Crazy Chester · Apr 26, 2020

I guess I didn't look hard enough earlier for studies on root temperature ranges within a hydroponic system, because this morning I found an interesting (but older) paper authored by a hydroponic farmer in Ireland in 1996: https://doras.dcu.ie/18523/1/Damon_Berry.pdf

Points made in the article:

1. A huge swing in nutrient solution temp is acceptable (up to a total of 45 degrees F);

2. A nutrient solution just slightly below air temp is acceptable (in areas with fairly mild air temps generally);

3. The bottom temp range of a nutrient solution for sufficient nutrient uptake is between 55 and 59 degrees F; and,

4. Both increased yield and earlier ripening is encouraged by higher nutrient solution temperatures, with up to 77F being found to be effective.

I take from this article some confirmation that my system should work fine with barely any improvement, but that it will work much better (increased yield and faster ripening) if I can get the low of the range of my nutrient solution temperature higher.

Luckily, I had already installed an aquarium heater that I set at its lowest setting (72F) and placed it in the bottom of the reservoir when I put the system in place - in case I needed it.

Now, I think I will use it.

The question in my mind is now "how much of a temp range do I want?" Theoretically, by turning on the heater, I can now keep my reservoir temp at 72F overnight and let it range to a high of 76F during the day - or, I can put the heater on a timer and try various settings to create various custom temperature ranges.

Perhaps I will find the full range without a heater works fine for veg, but that higher root temps during flowering (or at least towards the end of flowering) works best.

Eventually, my experiment will find what's optimal, but, at this point, it appears to me worth the effort because, even if my conditions turn out to be sub-optimal, I do believe whatever is produced will make it worthwhile to have done it.

Douglas.Curtis · Apr 28, 2020

15+ years says stick with 69F or your potential for issues will be significant. Considering you're outside as well, I would not even consider going outside the 65F/69F window. At the peak of flower, it only takes a few hours of not enough O2 to do extensive damage. There are many other factors at play in the study where 72F worked well.

I would use a thermostat controlled outlet with a probe in the reservoir. Set your temp at 69F and plug the aquarium heater into it. I would also look at putting it on a timer so it only comes on during the night, early morning.

Outdoor Hydroponic Rooftop Grow - Recirculating DWC - No Airstones & No Medium!

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