Room for Improvement

Each room holds three 10' x 20' pods. The yellow card hanging from the front light is a sticky indicator trap for aphids and fungus gnats. The ballasts mounted along the back wall generate unneeded heat. The reflectors, designed for air cooling, are not being used with an air-cooling set-up so they are also releasing heat. Lights are placed about 3 1/2 feet above the plant canopy so the light gets dispersed evenly.

The story of one San Francisco Bay area co-op supplier, Jimmy H., and his garden.

pic Ed Rosenthal

This article appears in Volume 5 – Issue 5 of SKUNK Magazine.

THE SAN FRANCISCO BAY AREA has a burgeoning medical marijuana community. Some patients grow their own medicine, but most have some interaction with the plethora of medical patient co-operatives popping up all around. These centers may be the source of their supply of bud or they may just be the source for clones from which they start and maintain a garden with medical quality plants. Co-operatives are mostly supplied by large-scale growers, who use 20 or more lights.


The following is the story of one co-op supplier, Jimmy H., and his garden:

“An acquaintance told me that he had a big space, which could be used as a grow. He had made arrangements with the landlord and we agreed to invest in the 10,000 square foot space together. I had years of experience growing and I thought this space would be perfect. It had good ventilation that was left from the last tenant (the space had been used as a sewing factory), and all the electricity and fans were already in place. The space needed only minor modifications to make two giant rooms for flowering.

“We used wood framing and black/white plastic polyethylene to create the spaces. Each room holds three 10’ x 20’ pods with 2½ foot walkways between them. The pods were made using 2’x4’s placed on the floor. They are lined with 30-mil butyl rubber, the same kind they use for fishponds, so they are totally waterproof.

“I’ve tried a wide range of growing methods. After experimenting with drip, constant flow and flood systems I went back to planting mix in containers because I found it to be the most convenient method of growing. The containers are placed on slats to allow for drainage. Each pod holds 392 2½-gallon containers. It does take some work at the planting stage, but it is very easy to care for and very forgiving. I tried all kinds of soils, too. I tried the least expensive house brands and also the expensive brands such as JR. Ultimately, I found the most inexpensive high quality soil to be Black Gold.

“I just add water while the plants are in growth stage, maturing from clones to young ladies. At three weeks I prune the plants and take cuttings. The plants are about 15” – 18” tall then. I cut the growing tip and leave the four healthiest branches, which are staked. I use the branches I removed for cuttings and put up clones using Oasis 1015’s. This is a synthetic material that wicks water and is sterile. A 10” x 20” nursery tray holds 50 cubes.

“After a few days of adjusting to their trimmed state and the loss of the primary growing tip, the light is changed from constant to 12/12 and they are triggered into bloom. I then begin fertilizing them by giving them Old Age Organic Growth Formula once a week as directed. I water daily, alternating with liquid kelp or bat guano rated at 3-10-1. Once in a while I skip a day of watering and I occasionally skip a day of fertilizing.

“Each room has four 40-gallon reservoirs, one at each end of a walkway. The water is plumbed to the reservoirs. We use little giant pumps to keep the water circulating. This keeps the fertilizer mixed and adds oxygen to the water. We pump water through a 25-foot hose to hand-water the plants. A reservoir holds enough water to fill a pod so three reservoirs are used in the room each day.


[pullquote align=”full” cite=”” link=”” color=”” class=”” size=””]“The perimeter is secured with rolls of razor wire inconspicuously hidden in shafts and crawl spaces. The combination of having employees working at night while the lights are on greatly discourages burglaries. The space is closed during the day.”  –Jimmy H.[/pullquote]


“To keep the humidity down, two huge dehumidifiers are used to condense the moisture. I use forced air (fans blowing air into the room) to maintain positive air pressure. Since the air pressure is higher inside the room than it is outside, air is constantly pushing out of the room through small vents as well as through cracks and crevices. This also makes it harder for insects and pests to enter the space.

“The rooms are set up with CO2 using tanks. An online monitor controls the rate of injection. I try to keep the CO2 at about 1200 parts per million. Rotating fans mounted on the walls gently blow air on the plants while larger fans blow air toward the ceiling.

“Less water is required when the plants go into bloom because the lights are off half the time. After the second week of flowering, I change the fertilizer to Old Age Organic Bloom. At this time straggly branches and new adventitious growth are trimmed off. Then we just baby-sit the plants for another four weeks until the buds ripen.

“We monitor constantly for insects and plant pests while removing big shade or fan leaves to allow the light to get directly to the bud. I use nematodes and yellow (aphids and fungus gnats) and blue (thrips) pest traps for monitoring, however my main problem was spider mites. I never got rid of them but managed to contain them with Safers Soap and neem oil. Mold has also been a problem. The mold grew when there was too much humidity and heat. Bringing in the dehumidifiers and positive air pressure eliminated the problem. I sprayed baking soda at one teaspoon per quart to control powdery mildew.

“Each pod uses seven 600-watt lamps and three 1000’s. The 1000’s are in the center of the pod and use an umbrella reflector so that the light spreads out over the entire garden. The seven 600’s pick up a lot of shade so that all areas have light. The ballasts are hung high on the wall. Unfortunately, they greatly contribute to the high level of heat in the room. If I had it to do over again, I’d move them to the other side of the wall.

“Speaking of heat, it is a big concern. All the reflectors except the umbrella shades could have been connected up to vent out the air. Each time a garden is created you learn how to make it better. At one time I thought this was the ultimate garden but now I see its shortcomings. It really needs air conditioning.

“I use two deodorizing tubs filled with deodorizing gel, supercharging its action by having a fan blow over it. I like the gels because they don’t mask the odor, but eliminate it. I also use an ozone generator by the front door.

“My partner knew a fellow with a unique strain called Coral Reef. The grower was reluctant to share the variety but we promised not to sell the clones, especially to the medical co-ops. We bought 1,000 plants at $20 apiece. I had 28 varieties at one time. We became particularly fond of the Max 49 and J27 and the Champagne. I dumped a lot of plants I should probably have kept, but after a while I got tired of them. I let the G-13 and Cali-O go, for instance. They’re still around so I guess I could get them back.

“To keep the area cool, the lights are on at night from 7 PM to 7 AM. Here in the East Bay, the temp cools 20 degrees at night. The lights were rewired to 240 volts, effectively lowering the use of electricity and the bill by one third. In other words, the light becomes a lot more efficient.

“The perimeter is secured with rolls of razor wire inconspicuously hidden in shafts and crawl spaces. The combination of having employees working at night while the lights are on greatly discourages burglaries. The space is closed during the day.

“We cut down all the plants in a pod after seven weeks and put them in a drying room with a dehumidifier. We dry the plants on racks made with screenings and also dry the leaves for the purpose of making hash and hash oil. We then trim the leaves off the bud, but don’t process it because other people in the area specialize in processing. All the bud goes to the co-ops for medical use.”



After telling me his tale, he asked if i would like to see the garden. We made arrangements to meet a few days later.

I parked the car on a commercial street and rang the bell, staring at the corrugated metal of the roll-up doors. My host opened a side door and ushered me in to the space. We walked through the reception area to a work/storage space. The doors to the flowering rooms were in this area. The mother plants and clones were usually upstairs, but the area was being remodeled. One room had been placed in flowering about a week before, although young plants were still being stuffed into the space as they were potted. The other room was forced about four weeks before.  

The work area reception area/work room was a cool 70 degrees, 10 degrees warmer than the cool East Bay evening. As soon as the door to the first flowering room was opened, a wave of heat hit me. The flowering room was 80 to 100 degrees depending on the spot. The heat from the lights was making the room too hot and there was not enough ventilation for it to be evacuated. The hotter areas had stressed plants, but the plants in the cooler areas were growing well.

Each 200-square-foot pod was lit by 7,200 watts of electrical input, an average of only 36 watts per square foot. The plants would have produced larger buds under 60 watts psf. Each pod could use another 3,000 watts. Alternatively, he could consolidate the pods to 120 square feet. He would be growing fewer plants, but have the same yield. This would give the plants the energy to produce thick, resin-coated buds.

I looked around. With a few hours of effort and not too much of an investment, this space could easily be turned around. The twenty-one 600-watt lamps in each room are designed so they can be used as air-cooled reflectors. Set up the air-cooled option by attaching flexible ducting to the lamps with fans blowing cool air from outside the garden area through the reflectors, where it collects heat. The hot air is exhausted outside the building.

Replace the inefficient vertical reflectors that hold the 1000-watt bulbs. They are very inefficient because they direct much of the light to the walls. Instead, use high quality air-cooled reflectors. The air-cooled reflectors and duct system prevent most of the lamps’ heat from entering the room. They will eliminate 1/2 – 2/3 of the heat before it gets into the room.

Get rid of the dehumidifier and replace it with air conditioning. If air-cooled lights were used the heat from each room should be cooled using air-conditioning. Air conditioners also work as dehumifiers, removing water from the air.


There are some other ways heat can be removed from the room (listed from easiest to hardest):

  1. Open the doors to the hallway and let some of the hot air out of the room and some of the cool ventilated workroom air in.
  2. There is a cork tile-hung ceiling hiding a 14-foot ceiling. Remove some of the ceiling tiles so the hot air can rise.
  3. Reverse the direction of the ceiling fans. Currently they blow hot air down from the ceiling. Instead, they should help the hot air rise to the top, then out of the garden.
  4. Turn on the roof ventilating fans to pull the hot air from the top of the room to the roof.
  5. Convert from magnetic to digital ballasts, which eliminates about 1/12 of the electrical usage and doesn’t create much heat. Move the ballasts out of the grow rooms to a space where their heat can be ventilated out. This will eliminate thousands of BTUs of heat from entering the space.
  6. Install a ventilation system drawing air from the back of the building to each of the grow rooms. The cool night air should be filtered before it enters the room. Excess air will be drawn out by the roof fans.


This garden has produced well before, during the winter and spring. However, Jimmy hadn’t prepared for the seasonal weather change. When warmer weather arrived the plants started suffering heat stress.

When he failed to take action to correct the problems the plants suffered and much of the crop was ruined. The main culprits were poor planning, lack of knowledge and perhaps greed. For one thing, he skipped on lights. But perhaps the biggest drawback was rather than learning how to develop an efficient system that consistently produces high quality medicine, his goal was expansion. Had he designed the garden based on the plants’ needs he could have grown a beautiful crop.


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