Barrel of Green: Compact Grow Box Overview

The concept of the “Barrel of Green” grow box emerged after seeing photos and reports of similar setups online. We knew the system worked, but believed it could be improved. We began researching ways to enhance ventilation, lighting, and cold air circulation inside the chamber. Now, we have a final, upgraded version of the Barrel of Green that is easy to build and maintain, and can provide a typical medical marijuana user with a sufficient supply of medicinal herb (up to 100–150 grams every 2–3 months).

Below is the complete documentation for the Barrel of Green plant system. Our goal is to show how easy it is to build and maintain this unique grow chamber. All system components can be found at your local hardware stores, markets, or ordered online.

Materials and Construction

Here you can see the plastic pots we chose for this unique grow chamber. The pots are 24 inches (610 mm) in diameter and 22 inches (560 mm) tall:

For ventilation and to supply fresh, cool air to maintain a moderate temperature of 60–65°F (15–18°C) inside the Barrel of Green, we used a 4-inch (100 mm) flexible plastic duct:

We used a utility knife to cut a hole in the bottom pot to make space for the 4-inch (100 mm) flexible ventilation duct:

The duct was then inserted through the hole we just made:

We added a 4-inch (100 mm) layer of expanded clay pebbles to the bottom of the pot. This provides soil drainage, allowing excess water to drain into the tray and preventing root rot from stagnant water:

For the substrate, we chose a mix of Pro Mix potting soil, perlite, and fine expanded clay pebbles. This is all we need for the soil mix, as we use Advanced Nutrients fertilizers for this grow:

We filled the bottom pot with the soil mix, placing the 4-inch (100 mm) ventilation duct in the center. We also moved the grow chamber into a closet, as the pot is now quite heavy:

Lighting and Ventilation

To control the heat from the 250-watt lamp in this compact grow chamber, we found a Pyrex Bake-A-Round bread tube (Cool Tube) on an auction site. This Pyrex tube can withstand high temperatures:

We placed the Pyrex tube on top of the upper pot and traced a circle around it. This allowed us to cut a precise hole in the upper pot so the tube could be installed in the correct position. Our 250-watt HPS lamp will be placed inside the Pyrex tube:

Again, we used a utility knife to cut the hole for the tube. Make the hole slightly smaller than the tube’s diameter so it fits snugly and doesn’t slip through:

The Pyrex tube is now installed in the upper pot. This is why it’s important to make the hole just a bit smaller than the tube’s diameter:

Here you can see how the tube sits inside the upper pot:

The next step is connecting the Pyrex tube to an exhaust system to remove hot air from the Barrel of Green. Without this ventilation, the temperature inside the grow chamber could get too high for healthy plant growth. Remember, high temperatures can reduce your yield and quality, or even kill your plants.

For lighting, we chose a 250-watt high-pressure sodium (HPS) lamp. The lamp is mounted in an E40 socket and suspended in the center of the upper pot. With this size lamp, we hope to harvest between 0.50 and 0.75 grams of marijuana per watt of light:

These 3-inch (75 mm) ventilation fittings fit perfectly with the outer diameter of the glass tube:

We used several other ventilation fittings and metallic tape to connect the other components of the ventilation system. It’s important to use flexible ducting, as shown in the image, so you can lift the upper pot and move the duct system whenever you feed or check on your plants:

As you can see, all ventilation components are assembled and installed on the upper pot. The 3-inch (75 mm) flexible duct vents heat upward through the attic above the grow closet. We cut a 3-inch (75 mm) hole in the closet ceiling and pushed the flexible duct through. All the heat now goes into the attic, away from the grow closet:

Here’s how it looks in the grow closet. The 3-inch (75 mm) flexible duct pulls air and heat through the ceiling. We cut 3-inch (75 mm) holes in the ceiling above the pot to vent hot air into the attic:

We used a rotary fan with a capacity of 65 cubic feet per minute (110.4 m³/h). It runs on 110 volts and is very quiet. This fan is excellent for removing heat from the grow chamber.

To prevent light leaks and maximize the efficiency of the 250-watt lamp, we wrapped the upper pot with a reflective material similar to “space blanket.” This material is excellent for reflecting light back, allowing you to get the most out of your power. Remember, in this Barrel of Green, we aim for 0.75 grams per watt.

Planting and Growing

We installed a circular wire mesh (2 inches x 4 inches / 50 mm x 100 mm) in the center of the lower pot. For this particular grow, we started with the “Oregon90” strain. The plants shown are clones taken from a female Oregon 90 plant. We gave them 18 days of vegetative growth before placing them in the chamber. This image shows the clones after one week of flowering:

We use Advanced Nutrients fertilizers for our grow. In the first week, we feed them Advanced Nutes Bud Blood to promote lots of flowering sites. From weeks two to six, we use Advanced Nutrients, B-52, Carbo Load, and Big Bud. In week seven, we switch to Advanced Nutes Overdrive, giving the plants one last boost to increase bud weight and mass. It’s very important to always monitor the pH of your water so the plants can absorb all the nutrients. Even if you’re just spraying your plants with plain water, make sure the pH is between 6.2 and 6.7. Otherwise, you’re free to use any fertilizer brands you prefer.

In this image, the plants are just over two weeks into flowering and are shaping up nicely:

As you progress, you’ll notice many new flowering sites. At this point, you should train new shoots around the circular wire mesh. You can also start trimming the plants for shape and arrangement.

Here’s another close-up with more detail:

I find that since Indica strains don’t tend to grow very tall and instead take on a bushy form, they are ideal for our setup. In the future, we’ll try growing a Sativa strain to compare yield, quality, and growth habits.

Here’s an image showing how easy it is to work with the Barrel of Green chamber:

We have a small chain above the chamber with two small hooks. When we need to work on the plants, we simply lift the upper pot and secure it on the chain with the hooks.

This image shows the overall planting in the Barrel of Green after 35 days of flowering. Most buds are 4–5 inches long and very dense. Many are already swelling with resin:

Here’s an image of the current Barrel of Green grow two weeks before harvest:

The plant canopy is over 16 inches tall, forming a solid wall of dense, rock-hard buds. This juicy, fruity strain is so covered in crystals and resin that it should be fantastic medicine for whatever ails you.

Harvest time came and went, and we’re happy to report a yield of 342 grams of wet buds. Growing in the Barrel of Green gave us 138 grams of dry buds.

For our next grows, we plan to try Blueberry, followed by Purple Ice, pictured below:

Additional Resources

Additional images taken from the author’s posts on the skunkmagazine.com forum:

Example diagram of the Barrel of Green grow box: