Tag Archives: growyourown

The Fridgegrow – closed loop growing with co2 support

Weed in a fridge

Flowering cannabis in a fridge
Cannabis that was grown in a fridge using the fridge grow

So when people think about starting to grow weed, they usually look at it from the beneficial side: It would cost less than the shady park vendor or the dispensary in nearly every case, especially when quality is taken into account. The overall quality is more controllable. Plus: In a world with PGRs, terpene spray, brix or artifical cannabinoids its still recommended by me to rather grow at home, than buying stuff simply because the packaging looks shiny.

The fridgegrow controller tries to fill a gap in the homegrow segment. Its not a fullblown all-in-one closet where you have little to no options in terms of light or nutrition, but its also not a tent, where you usually have to deal with environmental values as they come. When the door to the fridge is closed, its not possible to exchange air or even water from inside the fridge. (disclaimer: this is only half-true, but for simplicity we will assume this for that article.) You will have to bring some ingenuity into the operation!

The fridgegrow setup uses a few key elements to keep the environmental values in check:

The fridge

A fridge is able to lower the temperature inside its volume, without exchanging air inside the fridge. Lowering the temperature lowers the possible maximum of moisture the air can hold, water will condense on the cold backwall of the fridge and trickle down…
The fridges total power has to “work” against the grow lights total power, and therefore should be able to “outfreeze” the heat.
The fridge is not included in the system. I recommend to buy a beverage fridge for commercial usage with a closed front. You want to keep the light out. Make sure, that the fridge has as much power as you can get. Its easier to hold the values this way. Heres a fridge from amazon with a clear front, that has to be masked first.

A small heating element

A heater is able to work against the fridge to keep the relative humidity up. In a perfectly dialed in fridgegrow setup the heater will almost never run during the light-on phases, because light and fridge should cancel each other out AND holding onto certain humidity levels while doing so. This is also dependend on the total amount of water inside the fridge chamber.

The perfect light – crescience modular fluXengine LED built

There is no reasoning here for anything else than a high efficient LED setup. No asian amazon light or HPS light will be acceptable if your plan is to grow cannabis in here. Make sure you are able to remove the driver and try to place it outside the fridge. One thing I love about that built is, that I get to chose the light, and its not prebuilt in here!

LED grow light and flowering cannabis in a fridge
Crescience DIY LED setup -3x fluXengine board-style repping the Samsung LM301B chips aswell as a Meanwell – ELG-150-24A

For my fridge I have chosen a modular LED solution by Crescience. Crescience is known for their modularity and compatibilty to standardsized aluminium-framing. Its super-easy to build and you can actually achieve tailored photon-outputs for every system ever.
I am running 3 of their fluxEngines (link goes to the updated lm301h version) powered by a Meanwell ELG-150-24-A Driver.

Some thoughts about the fridge-light-interaction

The principle of continuity says: What goes in has to come out. This is true for everything that has a flow to it. In the case of the fridge one puts energy as heat into the system via the grow light and the heating element. The vapor-compression element on the back of the fridge is able to get heat out of the system and will transport it away through the heatpipes on the back of the fridge. Thats also the reason a fridge is hot in the back and cold inside. Our limiting factor for our light is the fridges compressor efficiency. If our fridge cant transport the heat away through its compressor the inside of the fridge will heat up endlessly, which will result in darkness since the controller will always try to save the plants, no matter if its “daytime” or “nighttime”. This means we need the most efficient and cool running light setup in here. A commercial beverage fridge for business will have a power draw between 90 and 150W from the wall. The light you use should draw a bit less than that.

Air circulation

Small fans directed at the back of the fridge are also an important element in this setup. It keeps the watercycle running smooth and steady. I have chosen Arctic 120mm PC-Fans . I connected them via a 4-way 3-pin fan-connector in parallel and a 12V/2A powersupply. If you are not sure about that, ask an electrician how to wire it.

fans in front of a fridge grow
Arctic PC-Coolers keep the air circulation going in the fridgegrow.

vertical nets or other vertical scrog systems

Keeps your growth in check! I had a few leafs touching the backwall of the fridge keeping the water from dripping down. This results in considerable pieces of ice in there, although its almost 30°C while the lights are on! Ice is bad. It binds water and takes it out of the waterloop.
I gave my plants only 4 glasses of water – in 67 days of growing. And this is a problem.

Scrog in a fridge
Basket-ScrOG system – the grow-space is very limited, so you have to expose as much buds as possible to direct light.

Feeding plants in a closed loop system

While a small windowsill plant doesnt need much to stay green and vital, cannabis under a blasting sun-replacement will transpire significantly more and will therefore have a much increased need of moisture. The trick is to catch the condensing droplets from the back of fridge and guide them back into the pots. Even if youre not able to do that perfectly, the water will still stay in the system, because of the fridges isolation. All you need to do is to close the small hole in the lower back of the fridge, where drops usually get vaporized through the compressor on the back. We dont want that, so we close the loop with a sheet of metal, guiding it back into the pots. This also has disadvantages: Im used to give diluted water-nutrition solution to my plants. Bio Bizz usually is diluted in a way that about 1-5ml of nutritional concentrate gets mixed with one liter of water. This is of course only true for system where the soil can dry out a bit and this wont happen in a fridge setup. You have to put in higher concentration (same amount of nutrition but on a glass of water) or you go for solid nutrition like greenhouse feeding or pre-grow formulas like Biotabs Organics.

I hold my plants in 3 gal smart-pots. Pathological amounts of greenhouse bio bloom and some biobizz was given, but i wasnt really able to conquer the ramping deficiencies my plants developed.

nutrient defincency on cannabis plant in fridge
Leaf discoloration and washed out leaf-tips: this plant was craving for nutrition.

Controlling CO2 – hacking sodamax/sodastream bottles

This is the first setup I was able to make use of extra CO2 inside a grow room. You first need to buy a CO2 bottle, that gets usually used for gassing up beverages mixed together in the kitchen. This bottle is under a standard pressure of about 6 Bar. The first connection has to go to a pressure-bottle adaptor. This adaptor is then connected to a pressure-reducer unit. The reason for that is the next element: its the actual CO2 valve that lets CO2 flow into the system: The CO2-magnet-valve that can be controlled electrical by the fridge-grow controller.

pressure limiter system
CO2 pressure-reducer: left you can see that the bottle-pressure is below 1BAR, so it will have to be replaced soon! On the left is the pressure measured, that lies between the magnetic-valve and the pressure-reducer: theres still CO2 available! But a second bottle would come in handy…

The Fridgegrow-Controller

This is the heart of the system. Its basically a mixture between a server (with a UI to check data and setup the environment ) and a controller. In principle the controller is just turning bluetooth-powerplugs on and off whenever temperature, humidity needs to be dialed in, lights to be turned on and off, or to open and close the CO2 valve. The system is pretty much plug and play and can be setup even if youre not really techsavvy.

fridgegrow controller
The fridgegrow-controller . In the back you can see the droplets of water that will eventually flow back into the soil. On the right-hand-side of the controller is the casing for the temperture and humidity sensor.

The controller will react to different parameters that are more or less dependent on each other. It will find a more or less stable cycle dependent on set values and the amount of water in the system.


The fridge reacts to two central reading: humidity and temperature. It will turn ON when ever the current humidity rises above the set value AND the temperature is high enough.
In this case that means that the temperature is at its set level or at max. 2x below the set hysteresis. A hystersis-value is the margin a value can go above or beyond.
So if you setup the fridge to hold a temperature between 24°C and 28°C (Thats 26°C with a hysteresis of 2°C) and relative humidity between 65% and 75% (set 70% with a hysteresis of 5%) the fridge will only start running when the humidity exceeds 75% while the fridge is between 22°C and 26°C.
The fridge will turn off when values below 70% relative humidity are reached or the temp drops below 22°C which is 2x the hysteresis. You can see easily that reaching the right relative humidity is dependent on the amount of water in the system. The fridge will never get below certain values if theres too much water to condensate.

Light control

This one seems easy: It just switches on and off at set-times.
But the system is also inhibitng fail-save measurements to save the plant. And heres the tricky part. The fridge can actually overheat while its trying to find a cycle, and thats a nono for the controller. It will turn of any heatsource that exceeds the global temperature limit. And thats the set-tempreature plus 2x the set-hysteresis. So in a running system with a 26°C ± 2°C the light will go out when ever the system breaks the 30°C limit to save the plants.
This can actually happen when theres not enough water around to keep humidity high: the heater will run longer to increase the amount of water in the air and will hit the temp-limit before the humidity levels can be reached. This will perodically lead to on/off cycles of the lights! So be aware of your cycles!

CO2 and Heating

CO2 is kind of entangled from the rest. The gas wont interfere with temperature and humidity and will be dialed in by the controller according to the set value and hysteresis.
The heater is your last bastion to figure out your values/moisture levels in the system. If the controller thinks, that a the heater needs to run WHILE the lights are on you have one of two problems:You need less water in the system!

The heater only reacts to temperature, so it will only go on, while the temperature drops too low. This can only be the case when the fridge runs too long against the light, trying to reduce the humidity. If you can dial up the light to create more evaporation the fridge will have a harder time reducing the temps, keeping the heater off.
If theres no use to it, and the humidity levels wont fall of with a constantly running fridge and a constantly running light, you have too much water in the system, so try to remove some. But this is basically the equilibium you want to achive: Running heater only when the lights are off, trying to get a stable water-humidity-temp equilibrium going.

The fridgegrow-app

One last word about the fridgegrow-app. To set everything up you need to be connected to the controller via the app or the controllers local webiste. If you dont connect the controller to your local wifi (which i recommend for safety concerns) you have to use the internal wifi from the controller. The controller guides you through the first setup of the remote-power plugs and is pretty easy to use with a standard UI and graphs of the sensor-data. Perfect for a nerd-grower like I am! In the graphic below you can see that i turned on three graphs, temp, hum and CO2. In the graphic you can see the exact moment when I opened the fridge at 19:15 or 7:15pm. the humidity and CO2 drops significantly as I pulled everything out of it, when I opened the door. The CO2 controller will turn on immediatly while you can also see the heating element tries to work against the fridge to keep the temp low.

screenshot of fridgegrow app
View through the fridgegrow app – setup your controller, check your values – remotely

Wrap-up: Should you buy a fridge grow?

For the beginners: Yes, its possible to just watch and learn with this system. Its really an accomplishment and a good amount of work to have it running stable for the first time, but you will be given a system were you have full control of every aspect of a run, while still be able to hold smell and noise in place.

Its for the nerd who grew weed in the past, but maybe dont want to have the whole fan/tent etc. infrastructure in his family home anymore. Maybe you want to get most of a limited space? This system got you definetly covered. I will try to harvest 100g dry regurlary out of there, and this should be enought to supply a single consumer out there and I am convinced that this system is working since I got my first 60g of Humboldt Seeds OGKZ out of there and it was a more than decent smoking experience. Welcome to the 21 century growers!

The Pro Grows: Blue Gelato by Barneys Farm – The 100l experiment

Why you should grow Blue Gelato 41

Derived from Thin Mint Girl Scout Cookies and Blueberry the Blue Gelato is another US based import to the European market under the distribution of Barneys Farm. The strain contains that mainly sweet and citric taste that Gelato is known for. Underlying with OG and Blueberry flavors you will get a …

(here I rolled a fatty to experience it another timer)

38°C on my balcony. The wind feels like a desert or caribian breeze. It all started with the selection of the particular flower. I decided to use one of the many top headbuds. The curing process was only three weeks in, the flower was as gluey as it gets and showed an incredible trichome density.

The effect delays into the second or third hit, subtle first but exponentially transforms to a truckload into the back of your head very quickly. The high is longlasting and top heavy. Side effects for me are a dry mouth and a big urge to eat some hot and spicy food.

(here I took another break to rest on the couch with some ice tea)

Items and tools

TL;DR – Blue Gelato 41

  • Strain: Blue Gelato 41 by Barneys Farm
  • From seed to weed: 141 days (veg 84 days, flower 57 days)
  • Wet harvest weight: n.a.
  • Final Dry yield: 244 gr (8.6 oz, single plant)
  • Effect: Strong, head heavy, numb mouth, clouded mind, psychedelic
  • Taste: sweet, OG, pungy

The Grow

Germination and Seedling Stage

When growing from seed you should always germinate more seeds than the actual number of plants you want to grow. Since I wanted to have one single huge plant I germinated two seeds and simply used the first one to show up as the main plant.

cannabis seeds
Blue Gelato 41 seeds

After about 0.5 cm of the initial root showed up, I put the seedling into a 3 gal smartpot with a fresh batch of BioBizz Lightmix. The first two weeks of a grow are always slow and boring: You dont really need to do anything but sit and watch. I kept the soil moist with my sprayer to prevent the seed from tilting from too much water. After the stem was strong enough, I turned to my usual watering schedule. This is also the point where I first give the seedling external nutrition. Lightmix already comes with a good amount of plantfood but for the remainder of the vegetative I gave her 2 ml of Bio Grow and 2 ml of Bio Heaven per liter of water. As usual I lowered the pH of my water dwon from 7.8 to the region bewtween 6.2 and 6.5.

Small cannabis plant in soil
Seedling a week after germination

Vegetative Stage – the long training

As you might know, I count the seedling stage into the veg stage. So the day my seeds get hit with water, I start counting veg days.

After 18 days the plant was ready for the top. I topped her once with intend and a few times by accident. I topped the plant right above the second node, so I ended up with four main branches, that will be trained outwards.

Cannabis plant in vegetative growth
After 18 days this plant was ready for an early top
topped cannabis plant
4 tops are left to be trained outwards
topped cannabis plant with LST applied
After three days the tops are ready for the bend!

Training setup is done! For the rest of veg I just had to train the shoots outwards again and again. four weeks into vegging I transplanted the plant into its final container: A single 100 liter unit! I decided to give her eight weeks to root through this volume.

Transplanted cannabis plant
Blue Gelato 41 after one month since germination in its final pot.

For this particular plant it was necessary to remove several side branches while it got trained further and further. The internodial distance was just to short, and even with this premeasurement the plant ended up being a nasty bush nontheless.

cannabis plant in a big pot
Bushy plant that needs some trainin…. (6 weeks old)
cannabis plant in training
…and after appyling LST (same day)

I wanted to play that out as far as possible and ended up with a structure that looked more like a weird piece of art than a plant.

heavy LST applied to plant
Heavy LST applied to a cannabis plant results in this structure. (8 weeks of veg)

The branches and the stalk are getting fatter by the day after 8 weeks of veg. The plan was to let her grow to the walls of the grow room and then upwards to encourage a bit of stretch once shes sent into flower.

cannabis plant and a ruler
My plant is 15cm tall after 10 weeks of veg.
upskirt shot of a cannabis plant
This shot shows what you have to deal with when doing something like that.

A few words why this method of growing cannabis is actually pretty dumb: So my grow room would be on top when it comes to economical grows. I use very efficient LED lights and do not bother with AC units or anything that impacts my electricity bill alot. I am still growing with under 400W of total power. But having a plant in this environment for that long kind of kills the idea of being economical here. Time is an important factor when it comes to economical growing, and what was done here was the opposite. The grow itself took close to 5 months to finish, while its possible to harvest more in just 3.5 months.

Flowering the beast

After 84 days of veg I pulled the trigger and started flowering. The branches did not really hit the walls of the grow room, but I thought the flowering stretch and a little bit of spreading would take care of that. Note that I defoliate pretty conservativley before flowering, which cant be seen here exactly, but my goal is, that every top gets direct sunlight.

huge plant
Blue Gelato 41 starting to flower.
detail shot of early flowers
Cannabis flowers in the earliest stage of development.

But I was wrong here: the plant had to support about 50 to 70 tops and stretching was not something she wanted to take care of. My assumption is, that the potential to stretch decreases heavily with the amount of top to put energy into to stretch. I got about 5 cm extra height overall, and thats it.

With the development of flowers, the plant now needs different supplements. So I switched from grow to bloom nutrition according to the BioBizz nutrient schedule sheet. I watered the pot with 10 l of water every 3rd or 4th day. Hitting day 21 of flowering I went for another round of defoliation, but I figuered out soon enough that this would not be enough for that lady. She kept putting out leaf material by the day, and I could grab handfuls of leafs far into the flower cycle. Most of the leafs on the back of the plant could not be pruned because I simply could not access that area at all…

cannabis flowers in development overview shot
Blue Gelato 41 in flowering.
macro shot of cannabis plant in early development
Resin production began early and heavily on that pheno.

Whenever you hit week six of flowering theres not much to do but checking trichomes and soil moisture.

maturing cannabis plant
Flowers of Blue Gelato 41 near the finish line

Although I had to deal with leafy colas the resin production on that strain is insane! After only 20 days of flower the colas were packed with trichs and after only 46 days I could already see trichomes turn amber.

trichome shot of cannabis
Day 46 of flower and the trichomes are already turning amber and are mostly milky. This one will be a fast runner!
cannabis plant closeup
Blue Gelato flower

Harvest, Drying and Curing

macro shot of harvestready cannabis
Brown pisitls, milky trichomes, and a good portion of amber ones: this lady is ready for harvest

So after only 57 days, six days before the harvest window given by the breeder, I decided to cut her down. Not only because she was ready, but I had to fight high temps in the grow room, and I did not want to risk any mold since that bush was so dense! pulling out a 100l pot out of that room was a pain.

bushy cannabis plant
The leafy backside of the plant, that I never had the chance to defoliate.

I decided to dry trim this time. So I cut away most of the fan leafs and hang her up branch by branch. After 7 days of this initial drying it was time for manicuring. This is mostly done by removing everything thats not flower material. But since the resin production of that one was so incredible dense I decided to keep a lot of sugarleafs on her. It was a rather experimental run in the end and I would not do it like that again, but a worthwhile experience!

cannabis dried and ready to smoke
Curing Blue Gelato 41