The Almost-Sealed Room

Everest casts his critical eye over blueprints of real indoor gardens and examines pros and cons with their designers.  Under the spotlight this time is Claude. He’s built what he calls an “almost sealed” room to produce heirloom tomatoes all year round. Will his set-up produce juicy fruits of joy or paltry piles of passatta?

THE SPECS

Environment

Temperature:

Day:  During flowering (up to the last two weeks) 83-85 °F (28-29°C)
Controlled by A/C – this switches on at 85 and switches off at 83.

Night: 72-74 °F (22-23°C)
Controlled by heaters and thermostats.

In the last week Claude lowers daytime temperatures to 70°F (21°C)  nighttime temps to 65°F (18°C) to simulate the fall.  This encourages ripening and enhanced flavors and colors.

Relative humidity is maintained at between 40-50%.

Photoperiod:  12 hours

Water source: rain water  (0 – 10 ppm) starting pH 6.6

Room Specs and Equipment

Dimensions: 28’ x 11’ ceiling height:  8’

Hardware:

• 10 x 1000W lamps with parabolic reflectors – the lights are suspended from hooks on the ceiling on pullies.
• 10 x 1000W E-ballasts with dimmer facility (housed outside of the room – with female sockets in the room.)
• CO2 generator – 8 burner.
• CO2 controller (PPM monitor.)
• 65 Pint dehumidifier  (you always need a dehumidifier in a sealed room – especially at night!)
• 5 ton (3 part) AC unit (compressor and fan are separate.)
• 10” carbon scrubber  (just circulates and purifies the air.)
• 10” inline fan with ducting.
• “Dump” fan – only comes on at night – 8” inline fan with 10” filter (with reducer.)
• 2 x 1500 watt heaters to keep nighttime temps up in winter.
• 75 feet of 10” ducting that runs around the whole room, dispersing the cool A/C air.  The holes are smaller nearer the AC unit, and larger towards the end for more even flow.  The holes near are 1” x 3” gradually getting larger until they get to about 1.5” x 5.5” – the holes are spaced about 8” apart and the ducting is right at the top of the room.  The holes are in the upper hemisphere of the ducting.
• 11 x 16” Oscillating fans moving the air between the tops of the plants and the lights.  (Not directed at the plants!)
• 6 x beds ( 5’ x 8’) made from 2 x 10’s with 5 1/8 ply bottoms on heavy duty coasters for portability.
• Growth media – 50:50 Promix BX (soilless mix) to perlite.
• 4” passive intake with damper.

Nutrient Solution Storage Room (aka “Res Room”)

This is completely dark and cool.
2 x 55 gallon barrels
One 8 stone air pump (4 per barrel.)
2 x 300W aqua heater (one for each barrel)
One float valve.

Nutrients & Additives

Base Nutrients: GH 3-Part
Floralicious Bloom, Liquid Kool Bloom, Dry Kool Bloom, Diamond Nectar, Pro Silica, Grotek Cal Mag.
Cal / Mag

THE INTERVIEW

Everest:  Hi Claude.  So we’re going to focus on the room you use for flowering and fruiting your plants. I see you’re using A/C to control temperatures and supplementary CO2 … and most people would presume you were trying to create a sealed growing environment, and yet you call your room “almost sealed” – what do you mean by that?  Did you purposefully design your indoor garden with air leaks or something?

Claude:  No, I just dump all the air in the flowering chamber every night when the lights go out using an extractor with a spring-loaded damper (to keep the room sealed when it’s not in use.)   All the air gets extracted into an adjacent room which I use for plants in vegetative growth.

Everest:  So if you’re so keen to get this air out of your flowering chamber, why do you “dump” it into your veg room?

Claude:  Because for six hours of the flower room’s dark period, the veg room has its lights on and so the plants in there can utilize this excess CO2.

Everest:  Ok, I get you.  What lamps are you using in your flowering room?

Claude:  When I first introduce plants into my flowering room I continue to use metal halide lamps as I have found that during vegetative and transition stages the metal halide produces much healthier looking plants.  But, once the plants start to focus their energy on flowering and fruit production the metal halide definitely starts to fall behind and it’s time to switch to High Pressure Sodium.

Everest:  Interesting.  I see you have your lamps arrayed in two rows of five.  Could you talk us through how you approached this room’s lighting requirements?  You say it’s 28’ x 11’ and lit with 10 x 1000W HID lamps.  Now, I’m sure you know the rule of thumb for growing light-loving annuals indoors:  40 Watts per square foot. 10,000 watts divided by 308 square feet gives you only 32.46 Watts per square foot.

Claude:  Yeah but not all of those 308 square feet are taken up by plants.  Some floor space is dedicated to auxiliary equipment like the CO2 generator, heaters and dehumidifer etc.  So I reckon I’m hitting your benchmark there.  The lamps are hung vertically within parabolic reflectors.  I find these give a broad and even dispersal of the light with fewer hotspots, even though they are stationary.  I have increased my yields by lessening the intensity and spreading the light over a larger area – even though some inefficiencies are brought into the equation by the fact that the light really has to be reflected.

Everest: And what are you growing your tomatoes in, exactly?

Claude:  I grow my toms in six beds filled with a soilless mix.  Generally I plant 48 plants per bed.  I use stakes and netting to provide extra plant support and I’m fanatical about pinching out and pruning too.  There is a 6” gap between the wall and between the two beds in the middle. The beds are on coasters so I can move them, allowing me to create an 18” walkway anywhere I like.

Everest:  Beds on coasters!  What was the thinking behind that?

Claude:  Well, it gave me the best compromise between filling my room with plants while maintaining a sensible space in which to work with them.

Everest:  What about drainage?

Claude:  (Looks sheepish)  Errrrm ….. there is no drainage.

Everest:  Whaaaaat!!?  No holes at the bottom of those beds?

Claude:  No.

Everest:  Who thought that was a good idea?

Claude:  I know, I know.  It’s not ideal.  I just try to water the bed as a whole.  One 55 gallon barrel does three beds.  I always use the same amount of water to moisten the soil, what changes as the plants mature is the frequency with which I water.  Maybe this isn’t the textbook method but it works really well for me.  At the beginning it may be as little as one watering every five days, but that soon works up to once every three days after ten to fourteen days.   It tends to stay at that for the rest of the cycle.

Everest:  I have to say that sounds a bit rough and ready.  How do you know what’s enough?  It’s not like you can do a weight test like you can when you pick up an individual pot – and you can’t see any run off.  Aren’t you worried about the lowermost roots getting all wet and anaerobic (without oxygen.)

Claude:  Well, it hasn’t seemed to be a problem so far.

Everest:  Well, I think that’s a major flaw in your set-up, Claude.  You’ve gone to town with all this lighting, AC, dehumidification, CO2, and you forget some simple drainage holes?  You absolutely must drill some in!  You could catch the run-off using trays under the beds, couldn’t you?  I’d be very surprised if you didn’t suffer from salt build-up in your media in the mid to late fruiting stage.

Claude:  You have a point there, Everest.  Salt build-up has been a bit of a problem and I end up having to flush through with water every so often.

Everest:  But how can you flush through if you don’t have drainage holes?

Claude:  Ok, point taken … I’ll sort some out.

Everest:  Right, let’s move on to your environment.  You seem to have this pretty well dialed in.  Your A/C unit keep things nice and cool, dehumidifies the air (with help from a separate dehumidifier unit) and the water collected by the A/C and dehumidifier drains into a tank, with a sump pump returning it to the reservoir to be re-used.

Claude:  That’s right.  Some growers say that the copper pipes in the A/C unit can contaminate the water but I beg to differ.  The PPM pen doesn’t lie!

Everest:  So walk me through your CO2 enrichment.  Aren’t you worried that you’re killing the planet with extra CO2?

Claude:  Not if my plants take it up, no.  I run a CO2 Generator when the lights are on, bringing the CO2 levels up to 1500 PPM.

Everest: 1500 PPM is too high.  I wouldn’t go above 1200.  Some old-timers I know won’t go above 1000 PPM.  They claim anything above that has an adverse effect on taste.

Claude:  Yeah, I’ve heard that too.  For the last two weeks of flowering I drop it down to 700 – again, I’ve heard a lot of different opinions on this – too much CO2 can slow the ripening of the fruit and produce an excess of green matter, rather than juicy toms.  At night, I run a dump fan – basically a small extractor fan – it dumps the excess CO2 (which the plants don’t need at night) into the veg room for the vegetative plants to exploit.

Everest:  How much do you run your dehumifier?

Claude:  Oh, that baby runs 24/7!  But it’s most important at night because in the daytime the AC does a lot of the dehumidifying – when it cools it dehumidifies.  At night, the temperature in my indoor garden drops which results in a sharp rise in humidity (air cannot hold as much water when it is cooler.) – The last thing I want is all that moisture falling out of the air onto my plants when they are in the final weeks of flower – I might as well just sprinkle mold spores onto my plants!

Everest:  Ok, let’s move on to irrigation.  You’ve got a little under 300 plants in your flowering chamber.  When they’re full of ripening tomatoes they must drink a heck of a lot.  How do you feed them?

Claude: I hand water.

Everest:  (Flabbergasted)  You whaaaat!!!!?  You’re kiddin’ me.

Claude:  Yeah yeah! I know what you’re thinking – I’m crazy but hey, it’s my passion.  And there’s method in my madness.  I live in a place where there are lots of power outages so automated watering isn’t so reliable or feasible.  It’s not as bad as it sounds.  I have two 55 gallon rain water barrels – each barrel has a float valve to automatically fill them from my outdoor cistern.  Each barrel has a 300W aqua heater keeping the water at exactly 68°F (20°C).  I have four air-stones in each barrel to keep my nutrient solution really well oxygenated.  There’s a pump attached to a hose with a water-lance.  When the beds are initially filled with soilless mix I water them in well with a ¼ strength nutrient solution and then leave the beds for an hour for the water to equalize in the media.  Then I transplant the plants into the beds and given a final small watering to welcome them in. One barrel does three beds.  I always use the same amount of water to moisten the soil, what changes as the plants mature is the frequency with which I water.  Maybe this isn’t the textbook method but it works really well for me.

Everest: Aren’t vertically hung lamps in parabolic reflectors a somewhat inefficient way to deliver light to your plants seeing as it’s virtually all reflected light that’s hitting them?

Claude:  Yeah – this is definitely a possibility / topic of hot debate, but so far I’ve found that the overall results in this set-up using beds and a large light footprint seems to be a good way to dissipate the intensity of 1000W lamps.

Everest:  So why do you use a small extractor at night (the “dump” as you call it.)

Claude: The purpose of it is to vent the excess CO2 and humidity at night.  I’ve found that leaving 1500 parts per million of CO2 at night seems to choke my plants out and cause yellowing.  It’s a good time to freshen up the air – plus, it’s a good idea to bring in oxygen as the plants are using more than they can produce at night.

Everest:  What is the pH of your nutrient solution?

Claude:  I adjust the pH to 6.2 in veg and 6.0 in flowering.  I believe that this is the correct pH for soilless media but when using mineral-based fertilizers it’s a bit of a grey area.

Everest:  Why do you use a lower pH slightly in flowering.

Claude:  Because P (Phosphorus) and K (Potassium) are more available at a slightly lower pH.

Everest:  True, the availability of P and K when using artificial growth media is higher at around 5.8, I even know some growers who drop it as low as 5.5.  Different strains of different plants have different needs but the standard range for fruiting veg is 5.9 to 6.5.

My best advice is to allow your pH to float within a range, say 5.8 to 6.5, at all stages of growth and to check the pH of your run-off too – then you’ll get a more accurate idea of the pH in and around the root zone.

Get those holes drilled ASAP and aim for 10 – 20% run off – whether you are watering or feeding, you are always trying to flush the media through.  In your final flush, run some water through a plant in a raised bed or container. Put a PPM pen in the runoff. You are shooting for zero PPM.

Claude:  Thanks Everest.