Behind the bolted steel doors of an old brick warehouse, Big Wes meets a nutrient company scientist to see if he can increase his crop yield. Rows of hydroponic marijuana plants soak up solution flowing through plastic troughs and light blazing from high-pressure sodium lamps.

Big Wes has spent more than half his life calibrating his system of growing high-grade marijuana to its utmost efficiency. At 50 years old, he harvests a crop of dozens of plants every week from five rented warehouses scattered along the rutted streets and alleys around the docks of Oakland.

His problem is that OG Kush, the ultra-popular strain he specializes in, produces notoriously low yields of bud per plant. For this reason the scientist has come with a nutrient solution made from deep-sea algae, which he promises will boost the output. Big Wes — who asked that his real name or certain identifying traits not be revealed because his career could land him in federal prison — is going to test it against his usual concoction, and try 15 different combinations of the two.

Photos: A higher grade of pot

Big Wes is new breed of cultivator, a “master grower” who produces marijuana that is potent and mold-free, tastes smooth and has a pleasing aroma — the kind of product now expected by ever-more discriminating consumers who frequent medical cannabis dispensaries.

He and others like him have revolutionized weed in recent years, growing sophisticated new varietals with scientific precision and assembly-line efficiency. Their expanding role in the burgeoning industry is shifting cultivation from clandestine rural plots to highly controlled indoor grows in urban centers.

“It’s kind of becoming the big leagues now,” said Kyle Kushman, a writer for High Times magazine and a grower who teaches organic and “veganic” cultivation classes. “Just like any other industry, as it gets older, the talent gets better.”

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Pot connoisseurs can talk about the complexity of cannabis like vintners do wine. They detect sweet flavors, and musky ones, and hints of berries, sandalwood, citrus, mint, pine and almond. An array of more than a hundred chemicals called terpenes brings out the taste and aroma.

Dusting the buds like a light snow are resin glands full of 80 or more cannabinoids, most notably the psychoactive one, THC.

According to George Van Patten, a.k.a. Jorge Cervantes, a renowned grower and author of the 484-page “Marijuana Horticulture: The Indoor/Outdoor Medical Grower’s Bible,” the many combinations of these chemicals produce a complex range of sensations.

“This explains why certain medical patients find more relief with specific varieties,” he said. “The THC molecule is the same in all cannabis plants. It is the mixture of other elements that play a vital role in changing the psychoactive effect.”

Two decades ago, most marijuana smokers bought whatever their dealer had. Now, in the retail environment that sprang up with California’s legalization of medical marijuana, they can choose from hundreds of strains of high-quality cannabis.

“Consumers have quickly developed a sophisticated palate,” said Andrew McBeth, publisher at the marijuana niche Green Candy Press. “Like fine wine, the marijuana must look amazing, have a distinctive bouquet and have the cachet of being a well-known and popular strain.”

The title “master grower” is part of the new marketing. The true connoisseurs scoff at the use of the label except in reference to a handful of the best growers in the world, like Cervantes.

But none dispute the high level of craftsmanship going into cultivation these days, both indoor and outdoor.

“All boats are rising,” Cervantes said.

Part of this is due to information. In the past, growers didn’t admit what they did, much less discuss their techniques. Now they have written dozens of books and penned a steady stream of articles in print and online. They even teach classes at pot trade schools like Oaksterdam University in Oakland.

Wally, in-house grower for a warehouse dispensary in Long Beach, spent years honing his skills on the underground market after realizing pot helped tamp down the tics he suffered from Tourette’s syndrome. A 36-year-old native of Santa Cruz, he first worked trimming the marijuana harvest for older hippies.

“I learned everything about growing, and I had a million questions and they were happy to share,” he said. “So many little tricks: They would run molasses in the last weeks of flowering to have sweeter buds. Or they went into caves in Santa Cruz to get bat guano and make it into a tea to put in the soil.”

He moved to Long Beach in college, and grew indoors wherever he lived. He learned by trial and error, inadvertently burning leaves when lights were too hot, shocking the plants with abrupt changes of nutrients or temperature, watching mold appear in poor ventilation, and fighting aphids and spider mites when he wasn’t vigilant about cleanliness.

Over the years, Wally, which is a nickname, grew to recognize the myriad subtle and changing needs of the herb. He could read the yellowing or wilting or drying of the leaves as too much of this or too little of that. He balanced nitrogen, phosphorous, calcium-magnesium, manganese, silica, molybdenum, bone meal, blood meal and dolomite — manipulating the ratios throughout the plant cycle. He learned to keep up the carbon dioxide during the flowering stage but cut it down in the last two weeks to keep the tight buds from blowing out like popcorn. Darkening in the leaf veins told him the plant was “begging for Epsom salts.”

He grew mostly for himself, while working at Bally Total Fitness. Then one day, he went to the warehouse dispensary with a couple of racks of clones he grew — plant cuttings that root and take life as new plants, which customers buy to grow at home. The owners were impressed by his skills and offered him a full-time job setting up their in-house grow operation.

The first three of seven grow rooms are expected to be operational in two weeks.

Much is riding on Wally’s expertise. The owners say they have invested $400,000 in the build-out so far, including $90,000 in air conditioning. They paid $15,000 in fees to be one of 18 dispensaries permitted by the city. On the three rooms, they estimate they’ll spend $5,000 on nutrients every six to eight weeks, and $10,000 in electricity every month.

If Wally succeeds, he should produce up to 80 pounds of medical marijuana every three or four months, retailing at $2,500 or $4,000 per pound, compared with $1,000 to $2,000 for outdoor-grown.

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In San Francisco, the owner of TreeTown Seeds, a thirty-something man named Nova, breeds his own new strains. He wears a cap with the title “Master Breeder.”

“You have to be a master grower before you can breed,” he explained recently at a coffee shop in San Francisco. “Unless you can grow it perfectly, you won’t know the genetic potential of a plant.”

Nova sells his seeds and marijuana bud to the top-of-the-line dispensary, Harborside Health Center, in Oakland.

His mind is an encyclopedia of marijuana. He spends most of every day in isolation with his plants, observing and smoking. He conjures Mendel charts in his head to see which strains might be bred together to make a better new one.

“I put everything into this,” he said. “When you’re a grower, you’re in a cave mostly. I’m like a monk.”

He takes a minimalist approach to growing. If he has a mite problem, he uses predator mites to get rid of them, not pesticides. He doesn’t put extra carbon dioxide in the room, as do many growers. And he tapers down the fertilizer a month before harvest to flush the buds clean.

“When you burn something and it crackles and sparks, those are signs there is too much nitrogen and phosphorous locked in,” he said. “It tastes horrible and burns your lungs.”

He said the rise of medical marijuana in recent years has allowed him to feel like he has a legitimate place in society, even if he still has to lie low to avoid federal law enforcement, which considers all marijuana possession illegal. For many years, he felt like a solo musician playing for himself.

“Now,” he said, “it’s like I’m playing in a band and we have a venue.”

Big Wes has a much bigger band and venue. He has three investors and nine full-time employees. He pays more than 20 part-time trimmers to keep up with a near continuous harvest.

He delivers his product to more than 50 dispensaries from San Jose to Sonoma County.

He is nothing like the old-school hippie grower. He commutes to Oakland from out of state and, with his crew cut and athletic build, would be pegged as a “narc” at a pot convention if narcs didn’t even bother trying to blend in. He voted Republican until a few years ago and owns a company that deals in the realm of corporate seminars. When the economy kneecapped that business, he decided to turn his side gig of growing marijuana into a real business and set up shop in California.

“We’re trying to professionalize and perfect this business as much as we can,” he said. “We’re creating standards and procedures. If you’re a dispensary, I can now provide medicine every week.”

He says he is in full compliance with California and Alameda County medical marijuana laws, although the laws on cultivating are murky.

Unlike many growers, Big Wes’ three full-time “reps” don’t show up at dispensaries in T-shirts with backpacks full of weed. Instead, like their pharmaceutical counterparts, they dress in business-casual and carry briefcases with sample jars of the product, along with lab results showing it contains no molds, insect parts or pesticides. They take the rare precaution of having dispensaries sign paperwork, he says, so they can show they’re in compliance with California law.

Part of Big Wes’ challenge is to bring his output to about 1-1/2 pounds of bud every 14 weeks under each of his 300-plus lamps, so that he can still pay his $35,000 monthly electric bill, among other costs, as more growers enter the market and the price of marijuana falls. It’s not an easy business, he says. A friend of his thought it would be, investing $2 million in lights and equipment, only to give up after a series of subpar grows.

And in Northern California, the high price and environmental cost of indoor marijuana have produced a small backlash, with some consumers now preferring North Coast sun-grown pot.

But by perfecting his delivery efficiency and sales technique, Wes is building something he suspects might be more valuable than the marijuana itself in the future: his distribution network.

“If I could have the largest distribution of the largest cash crop in the world’s eighth-largest economy, what would that be worth?”

joe.mozingo@latimes.com