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Advanced - Screen of Green (SCROG)

Can you give an example of a SCROG cabinet?

The Setting

For those of you who can grow in a 10' room under 1000 watt lights, I envy you, but many of us can't devote that much space and effort to pot growing. We've been chatting here for many moons about micro cabinet growing, and I'm a big fan of the concept. But for those interested in some real production, I'm talking 1/2 pound to a pound or more every crop, I can show you how to do it easily in 2-4' of wall space.

I'm proud of my system, and of the yield, and I have good reason to advocate the specific methods I've practiced. But there are many ways to skin this cat, and I don't mean to offer a solution for all time, just one. One that works.


Your Space

We start with a wall. You need airflow through the cabinet, so an outside wall is best. You need to be able to get air into the cabinet, so if you can punch holes through the wall with a hole saw, all the better. You need to get air out of the cabinet as well, so if the eave / soffit line is accessible, that's a great place to dump air.

It helps if the cabinet is not the only thing on the wall. A wall of cabinets, with our factory just being one of the bunch, is perfect; hide in plain sight, basic Sherlock Holmes [a later reply suggested that 8’ cabinets are unusual and not too stealthy as a result - ed]. But a couple of cabinets standing by themselves will not look out of place in a garage or storage room, particularly if they are surrounded by tool racks and other normal clutter of a working space. With all the recent chat about refrigerators as growing cabinets, that might be the first place I would suspect!

Each cabinet takes up 2' of wall space. Why 2' and not some other dimension? Because the engine of this factory will be the 250 watt HPS, and that is a light that can best handle a space about 2' square, 2 1/2' tops. Further, standard size storage containers, which are used for growing and for reservoirs in this system, fit right snuggly into a 2' interior space.


The Cabinets and Utilities

Note: The incoming power source should be on a GFCI circuit. If you wire up wall sockets around the cabinet as I did, only the first one need be a GFCI. All the other power outlets can take off from the first GFCI circuit. Never gang up GFCI circuits. If you are using power cords, buy a GFCI stub cord and put it in the main line. Transformers, motors, submerged pumps, HID lights; a recipe for fire or shock. You have been warned!

Each cabinet system occupies a footprint of just about 2' square. A standard floor to ceiling height of most finished spaces is 8', which is just right for this setup. I recommend plywood for the walls, as insulation is not necessary, and the thinner the walls, the more room for buds. You can design hollow spaces in the cabinet walls to carry electric power if you like. I ran a power supply wire into the hollow walls of the cabinets and installed standard wall switches and outlets to supply power to the various systems. It isn't necessary to be so neat, but it appealed to me, so I did it. You can supply electricity with cords snaked up through the floor or from a nearby wall plug, so long as the wire is sufficiently thick; at least the same gauge as the wall supply, and you will need at least a 15 amp circuit with little or nothing else on the line like maybe a garage light).

Water is a nice luxury if you can plumb a faucet outlet into the cabinet next to the reservoir; a drain would really be cool. If not, being able to run a hose to the cabinets will save a lot of time. I don't have water in my cabinets, but I can drag a reel hose into the outbuilding I use easily. I use quick connect fittings to connect the hose to the reservoir for topping off and filling.

The doors need to fit nearly airtight, but not perfect, as the fan blowing air out of the space creates a slight vacuum that sucks the door in. It would be better to create an overpressure in the space, but that complicates sealing the doors quite a bit, so I recommend the ventilation fans suck air out of the cabinets rather than blowing in. I sealed the doors in my units with foam weatherstripping, using strips of 1 x 2 boards to frame the opening and mounting the foam along the 1 x 2's. The board strips were mounted on the interior walls so that the foam stood slightly "proud" of the outside of the cabinet, allowing the door to crush the foam slightly as a seal. The foam also effectively seals the light inside the cabinets. I can stand next to the cabinets in the pitch dark and see only a few tiny cracks of light coming out around the hinges, where I didn't get a perfect seal.


The Basic Layout

Let's first focus on a single cabinet, taking up 2' square of space, 8' tall. We'll need three separate compartments in the cabinet, each with its own door to allow working in one compartment without blowing a dark period in another.

The top compartment is for flowering, and should be 4' tall. Why on top and not in the middle? The heat will be generated by a 250 watt HPS light in the top of the cabinet, and that heat needs to be removed. If the light was up against the floor of an upper cabinet, it could roast the roots of the plants above. Heat rises, so let's put the biggest heat source as high as possible.

Why should the flowering cabinet be 4' tall? Because if you follow these plans, the relationship between the height of the container, the stem length to the scrog canopy, the thickness of the scrog canopy, the distance between the lights and the canopy and the thickness of the light hood fits almost ideally in a 4' tall space. It would be difficult, in fact, to change the relationship between the elements of the scrog system with a 250 HPS light. 4' is not the minimum space required; I get by with 44" in one cabinet be stealing an inch or two from the stem length and the light gap. But more than 4' is probably wasted.

Next in line is a mother compartment, to be lit by a single 70 watt HPS bulb. I'm currently maintaining 8 mothers under the one small bulb, more than adequate [correct pruning is the key - ed]. The 70 HPS runs very cool, but even so, this mother space needs to be ventilated.

The height of the mother cabinet is negotiable. First subtract 4' for the flowering cabinet (no less than 44", trust me). Then figure the space needed for the reservoir on the bottom. Include some air space above the reservoir for access to mechanicals. The leftover height goes to the mothers. They don't need much. Probably the minimum height would be 2' or so.

Cloning can also be handled in the mother compartment by installing a small shelf on the upper part of the wall; nice and warm up there, good for rooting. I mount a 20 watt stick floro above the cloning shelf, a recent addition just for the hell of it. It was working OK just with the side-lit HPS. Cloning only happens every two months, so the shelf could even be made to fold up against the wall when not in use, allowing more space underneath for another couple of DNA storage units (mothers).

Finally, heat rises, but water runs downhill, so the lowest compartment holds the reservoir. An 11 gallon Rubbermaid storage container is the perfect size.

There you have it, an integrated system of mothers, clones and flowering plants, all in a 2' footprint. I get about 2 ounces per foot of scrog canopy with a 250 HPS, so we're talking 1/2 pound per crop here on a good day.

But, let's take this a little further. The mothers only need to produce 4 clones per crop, and are obviously capable of making many more. So, how about another 2' cabinet next door? Two more 4' tall flowering cabinets could easily be supported by the mothers, and now you're talking 1 1/2 pounds per crop. That's 3 ounces per foot of floor space, mothers and reservoir included.

I have a second cabinet, but three crops at once is more work than I care for, and the electric load of the lights and fans probably is excessive for a 15 watt circuit, so I modified the plans a bit, and built three compartments. The bottom compartment holds a second reservoir and pump, which allows more time between topping off than if one reservoir was servicing the whole unit; I'm lazy. The middle compartment is another 4' flowering cabinet, but note that it overlaps the mother cabinet next door and shares part of the wall of the upper flowering cabinet in the first stack.

I cut out a passage way in the shared wall, so that the two flowering cabinets both share the same air system, a 200 CFM Dayton pancake mounted in the top of the upper flowering cabinet. To help the airflow along, I mounted two 100 CFM axial fans in the passage way. I can light proof the passage way by mounting a darkroom air grill, a special plastic baffle that allows air to pass through but blocks light. The damn things cost a fortune, but they work well. That allows me to flower in one cabinet while the second cabinet is working vegetatively. Usually the two cabinets are in flowering mode, and I remove the darkroom grill to assist airflow.

That leaves 2' on top of the second cabinet; guess what goes there? How about the ballasts for all the lights? Keeps the heat from the ballasts out of the plant spaces, and eases the load on the fans.

By using two flowering cabinets, I only grow about two ounces per square foot of floor space, including all
reservoirs and mothers. I don't think most room growers include the mother area in their yield-o-rama reports, so I bet this system stacks up pretty well even against the 1000 watt crowd, except for the real pros getting 3-4 ounces per foot.


Ventilation

I am fortunate in being able to punch holes right through the outside wall to bring fresh air into the space. I drilled two 3" holes with a hole saw in the bottom of the lower flowering cabinet, and installed a short section of 3" PVC drain pipe through the wall. On the outside of the wall I mounted dryer vents with the air inlet pointed down, and a screen mounted to keep bugs out. I painted the PVC tube and the inside of the vents with flat black paint to limit reflected light. Amazingly enough, the bright sunlight is only 3" away from the dark interior of the cabinet, and I have no problem flowering.

On the inside, I clamped fabric shop vacuum bags over the ends of the PVC tubes, which protrude into the cabinet a bit for that purpose. The vacuum bags keep the "borg" out (mites), as well as stray pollen from unwanted male suitors growing outside in some neighbor's back yard [or clouds of hemp pollen from Canada! - ed].

Moving over to the first cabinet stack, the mother compartment is serviced the same way, but I only use one 3" opening. Airflow from the lower flowering cabinet next door is sufficient as an inlet in the upper flowering cabinet, but I did add one 3" inlet for use in summer, when some additional cool air is welcome.

I use 200 CFM Dayton squirrel cage fans both in the mother compartment and the upper flowering compartment. If we're designing a system with three flowering cabinets, I would use one in each. These fans are compact, easily mounted with integral tabs flat on a wall, and they are efficient and quiet. The big Dayton may be a bit of an overkill in the mother compartment, but it's easier on the mechanicals to use a large fan on now and then vs. a smaller fan huffing away all the time.

The fans have a square outlet tube that fits into nothing I am aware of; why do they do that? In any case, I stole the aluminum tube that comes with the dryer vents I use, flattened it out into a sheet and molded it into an adapter, converting the square hole of the fan outlet into a circular opening to insert inside a piece of flexible dryer outlet hose. I just used duct tape to strap the whole mess together. OK, it's not very sano, but it works.

What about CO2? There is little room for the mechanicals, the scrog blanket will already get as thick as it can be, and the fans are on quite a bit with the hot lights in the enclosed space, and would blow out the CO2 regularly (every five minutes or so). So, I doubt it would be useful in this limited growing situation.

The outlet is also a 3" PVC pipe punched through the wall. The inside protrudes into the cabinet as a place for the flexible dryer conduit to be clamped. The outside outlet is another dryer vent, with the flap pieces left in place to prevent insects and debris from floating in through the outlet tube. I ran the outlet right out through the eave line in the soffit, where it exhausts into some bushes.

What if you don't have the luxury of being able to tap the outside air so easily? Well, you can draw air from a crawl space if there is one below the cabinet, by running 3" PVC tubing up inside the cabinets to the desired compartment. If you use Rubbermaid 11 gallon containers mounted sideways, there will be enough space in back to run several such conduits. I ventilate the mother cabinet like that. The same holds true for the outgoing air. The fan can exhaust down a 3" PCV pipe into the crawl space, and flexible tubing can carry the air to the nearest available hidden outlet. You can't run air through tubes that are too long, or the fan won't be able to push the air needed. But I have tested a run of over 20' with no problems. I didn't use it, but the fan moved the air easily.


Controls

The fans need to be wired up to thermostats as controls, a humidistat too, if you can afford it. I use both, but I find the humidistat wasn't needed, as there is frequent enough airflow through the cabinets to avoid high humidity.

When selecting a thermostat, I recommend you avoid cheap units and get something decent. I use the industrial gray Dayton units with the exposed black coil. Damned expensive, but they work very well, keeping the temperature within a range of a few degrees from the setting. I used cheaper units at first, but the things allowed the temperature to fluctuate all over the place, and I ripped them out in disgust.

We want to mount the thermostats up high in the cabinet, where the buds will be growing, as that is the airspace that is critical. Generally a temperature of 70-75 degrees is recommended, and the combination of the Dayton 200 and the good thermostat nails it on the button. I sound like a commercial for Dayton products. Little do they know... [I bet they know perfectly well! - ed.]

All the lights and pumps are controlled by cheap hardware store dial timers, which I plug into wall sockets I built into the cabinet walls. These timers are junk, but have failed on me only once (costing me an entire mature Durban sea of green crop while on vacation, you bastards!). I have considered more expensive, and presumably reliable, timers, but haven't done so yet. Although the ballasts are by themselves in a separate compartment, they started off sharing the flowering cabinet space, and the outlets and timers are all still located there. That means I have to run some power cords from the timers through the walls into to the ballast cabinet, but it doesn't look too messy; there are already cords coming from the ballasts to the light hoods.

The reservoir cabinet has its own outlet and timer. I run the pumps for both reservoirs and the air pump from a single timer.


Water

The bottom compartments hold the reservoirs, and 11 gallon Rubbermaid storage containers work great. They will be in the dark, but it's not a bad idea to wrap them in black plastic to keep all light out, which prevents the growth of algae [also for the growing containers, of course - ed]. Cut out a window to check for water level of course. I use submerged Little Giant type pumps. The 8' compartment stack requires a pretty hefty pump, as there is quite a vertical distance for the water to climb. The pumps show how high they can push water on the side of the box. Again, go more robust than you need to provide a cushion.

1/2" drip system tubes work fine to deliver the water up into the cabinets, but you can also use hard-wired PVC plumbing bits and pieces, and there are adapters to mate the two. If you use PVC, go 3/4" to allow the water to mix with air on the drain leg. I used 1/2", but would go larger if I was starting over.

The water needs to get from the plant containers back down into the reservoirs, and gravity handles that. There are myriads of ways to plumb the system. I choose open drain holes cut into the floors of the compartments. I use Rubbermaid containers to grow in, and mount a cheap chrome sink drain in the bottom of the containers (more hole saws to buy). The chrome drain piece sits in the hole in the floor and drains into a large PVC adapter fitting that is plumbed into the drain system, all connected together and flowing back into the reservoir below.

For a long time I relied solely on the action of the water splashing down the drain tubes and into the reservoir to aerate the solution, and it works fine. But when I added the second flowering cabinet next door, with its own reservoir, I lost that effect due to the short distance the water falls. So recently I added a good quality aquarium air pump connected to an airstone in each reservoir.

Every couple of weeks the reservoirs need to be drained, and while you're plumbing away here, add a fitting to the cabinet to connect a hose, plumbed into the pump outlet line. That way you can connect the hose, turn on the pump and allow it to drain the tank to the outside. The hardware store is an endless source of valves and connectors to fulfill any elaborate design you like, to get water in and out of the reservoirs. I plumbed in valves in each compartment as well, so I can isolate one compartment from the water system during maintenance, etc.

Water is added to the reservoirs with a 1/2" drip tubing piece connected to a quick connect hose coupling. The drip tube piece pokes through a hole drilled in the container top (yes, another hole saw to buy). Filling up is clean and easy. Nutrient mixes are added from a jug with a piece of the same 1/2 drip tubing mated to the top. As I mentioned above, I plumbed in a valve and outlet in the line from the pumps in order to use the pumps to drain the reservoirs out through a hose for changing the water. I do so every two weeks.

Vacations present a special problem with such small reservoirs. To avoid having a friend or two watch over the grow (the less people who know, the better), I added a McMaster Carr brass float valve assembly to the Rubbermaid raised lid. That could be connected to a hose, but the consequences of an open hose leaking or a connection breaking gave me the shivers. Instead, I bought a 30 gallon storage container as a supplemental vacation reserve. I place it on a shop table and it gravity feeds the McMaster Carr float valves. If it blows up, I will only have 30 gallons leaking, not the contents of the entire Seattle water system. I don't normally use the float valves for water input, as they maintain the water level a bit below full, due to the clearances involved with the float.


Let There Be Light

You already know this, but the main engine here is the 250 watt HPS. I experimented with MH and enhanced spectrum HPS bulbs, but found the basic HPS can't be beat.

The standard hood for sale at the local growstore is just about 2' long, a perfect tight fit, covering the area completely with reflected light. There is no need to mount the hood on chains or anything like that. The vertical distance in scrog growing is fixed, so the hood can be screwed right into the top of the apartment (I mounted the hoods using wingnuts in case of maintenance, etc.).

The 200 Dayton pancake is thin enough to fit along the top wall of the cabinet in the dead airspace on top and along the side the light hood, allowing it to grab the hottest air to move out of the space. I ventilated the hood (drilled holes in it) to encourage the fan to draw hot air out of the hood, and you can probably do better if you like. A vented hood will probably not work in this space; not enough room on the end.

I suppose the light could be mounted to run into the cabinet rather than side to side, but it's easier to maintain the plants if the container is in front of the cabinet, with the air and water supplies running up the back wall.

To allow the hoods to be removed for maintenance (like oiling the Dayton fans), I connected the light socket to the ballast outlet cable with three-prong plugs and sockets. Unplug the light from the ballast cable, spin off the wingnuts holding the hoods to studs mounted in the ceiling of the compartment, and the whole light assembly comes out in one piece.

While the 250 HPS does a great job in this space, they tend to sit offset on one side of the hood, favoring the scrog canopy nearest the socket. I recently supplemented my hoods with a 70 HPS light mounted on the other end. It probably wasn't necessary, but I was frustrated by not having any more projects to do, and it was fun to engineer.


Plant Containers and Medium

You don't have to grow this way, but I'll advocate this method for one simple reason; it works, and it works as well as it needs to work. I couldn't grow thicker scrog canopies that I am producing now, so why fight it?

I use 11 gallon Rubbermaid containers to grow in. As you know, I grow scrog style, and I can't imagine using any other method in a cabinet. You can't possibly beat scrog for production, since the scrog canopy totally fills the space with buds. There just isn't room for more plant weight, so there's no need to look beyond scrog for the answer.

The Rubbermaid containers solve many problems. The drip system doesn't have to be water tight, because leaks are confined in the container. The scrog net can be attached to four poles attached to the corners of the container. The Rubbermaid container has a lip around the edge. I drilled a hole in each corner, inserted one of those plastic plant stakes in each corner, and just ran duct tape around the outside of the container to hold it all together. Simple, although I grant it's not very elegant. But if the compartment needs maintenance, the drip system inlet can be disconnected (quick connectors again), and the whole plant mass, scrog net and all, can be lifted out of the cabinet in one move. If you connect the scrog netting (chicken wire) to the walls of the cabinet, well, you can't do that obviously. Boy, has that come in handy on occasion!

The medium is, and isn't, rockwool. Yes, I use rockwool, but it doesn't act as the primary nutrient carrier. Four plants adequately support the scrog canopy, each started in 4" cubes. The cubes sit on a slab, but the slab is first sliced in half, just a thin layer. The purpose of the slab is only to spread the roots out horizontally, as the grain of the slab runs 90 degrees to the cube.

The thinned slab sits on top of an open plastic grate, an eggcrate grill for a fluorescent light fixture is perfect. The plastic grate is set up off the floor of the container on blocks, allowing a 1-2" air chamber for the roots to grow into. The roots quickly grow through the cube into the slab, spread out and then grow through into the bottom of the container, pooling up into the indentations molded into the Rubbermaid bottom. It is the flow of water over the roots in the container bottom that primarily supply the root mat.

Accordingly, I don't recommend a drip system, but an open flow, using spaghetti tube connectors as emitters. I recommend five half hour cycles per day, three during the light period and two during the dark period. The rockwool gets saturated with water, but the solution drains through the wool very quickly, flowing down the drains back to the reservoirs. There is never any build up of salts in the wool to worry about, and the roots will be very happy. Every time I clean out the system for another run, I pull a complete negative mold of the bottom of the Rubbermaid container made up of a creamy white plush root mat.

Is this the perfect method for all time? No, of course not. But it supports the scrog canopy to the maximum thickness that is possible in this space, and that's all you can ask. This system is simple to run and basically foolproof. An ebb and flow system could easily be run in the same containers, but the plumbing gets more complex, doesn't it? So why bother?

Note that since there isn't much mass of rockwool involved (less expensive too), I think the ESU and other solutions designed for rockwool are too acidic for this system. I've switched to GH dry [ABC series - ed], and I'm very happy with it. My plants show no nutrient disorders with the GH bloom and micro nutrients right at the recommended level on the packages (it works out to about 1000 PPM). Like I said, I couldn't grow more or thicker buds without growing into hyperspace, so why get creative? [Because there may be a better way; v-scrog - ed].

Mothers are also grown in the same fashion, but I skip the half slab. I can cram many mothers into the Rubbermaid tub, as they are never allowed to get very tall or big. In order to keep a mother small over an extended period of time, it is necessary to avoid giving it a ``haircut'', as that would encourage it to become bushy and top-heavy. Instead, remove whole branches from near the bottom of the plant, oldest branches first. Eventually a mother will get tired and will start to fail due to the many prunings, but she can always be replaced with a clone. I savage the mother compartment weekly, paying special attention to removing large fan leaves to deny the mother the growing energy they produce.

The mothers get the same solution that the flowering cabinets use, most often a bloom formula. They don't seem to mind. If there was a society for the prevention of cruelty to plants, I would be on the most wanted list. The mothers get little space or light. But I am cautious to avoid bringing contaminants into the mother compartment, since it contains a lot of precious DNA that needs to be preserved over years of time in a tight, enclosed space. No tobacco smokers (mosaic virus)! And I'm careful to do mother maintenance first, before yard work and other activities where mites and other nasties can be picked up.

If a disaster does occur, and the ``borg'' start to assimilate the cabinets, they get a taste of the famous PCO fogger, which is absolutely a miracle in enclosed spaces like this; resistance is futile. I have only occasional, and short-lived, problems with mites.


Conclusion

I could discuss many other bits and pieces of the system, but hopefully this has been sufficient for you to get the basic idea. I don't think you can design any other system that will produce more weight of buds from 250 lights in this space. I know that for a fact, because I've seen the scrog canopy that results, and it cannot be increased [I spoke too soon - ed]. If you are new to this hobby and you want to go first class in a minimum of space, you can feel confident that your efforts will succeed in a big way if you duplicate this system. If you choose to do something different, at least I hope my experience will provide some ideas for your dream cabinet. Thanks for listening.