indoor cannabis growing techniques

Cannabis cultivation laws vary widely state-by-state. Also, we can’t stress this enough: Growing cannabis is illegal in a lot of places, and the penalties — which include steep fines and prison time — can be much worse than possession, since growing can imply an intent to distribute. Black and brown folx need to be especially scrupulous about heeding these rules, since law enforcement targets us way more than white people for weed-related charges, even if we consume it at similar rates.

That said, when your plants are fully flowering, you might find yourself watering them daily, based on these indicators. When you do water them, keep going until you see water running off the soil, to ensure the water reaches all of the soil in the pot.

When the pandemic hit, many of us turned to quaint pastimes to soothe our existential dread, whether it was baking sourdough, knitting, or doing jigsaw puzzles. If you want to expand your repertoire of distraction methods with an activity that still has that quiet, homey vibe, but with a bit more of an edge, consider growing your own weed.

Before you get started.

Since clones come from plants that have been grown indoors, let yours chill in a shaded area for a week before exposing them to full sun, Johnson says. “The clone hasn’t tasted sun like that, and the transplant itself will be stressful.”

While you can absolutely grow cannabis indoors, outdoor cultivation is much simpler and cheaper, says Ron Johnson, author of How to Grow Organic Cannabis: A Step-by-Step Guide for Growing Marijuana Outdoors , who also runs the website The Cannabis Gardener. “The sun is free,” he tells Mic. “You don’t have to pay hundreds of dollars a month in electrical bills.” An outdoor garden probably won’t allow you to turn over product fast enough, but it’ll suffice if you just want to grow weed for yourself. Plus, it’s gentler on the planet.

To check if your cannabis is ready for trimming, perform a break test on each branch. If it bends so much it nearly breaks, then it’s ready, and if it breaks right away, it might be overly dry, but still totally usable. Trim off the buds and seal them inside a mason jar for curing, opening it periodically over the course of about four weeks to let moisture escape. Johnson outlines a detailed schedule on his website, including instructions on how to look for mold.

Cannabis plants can be either male or female. Female plants yield the plump flowers, a.k.a., “buds,” that we know and love, brimming with psychoactive compounds like tetrahydrocannabinol (THC, which gets you high), Modern Farmer explains. Male plants yield much smaller flowers, which people typically don’t consume. In other words, if you want to actually indulge in your crop, you’ll want female plants.

Your cannabis will be ready to harvest at around October. You’ll know they’re ready when the buds “start to get really, really swollen and packed pretty tight,” Johnson says. But it can be hard to tell if you’re a beginner. Many growers say that if you think your plant is ready to harvest, wait two weeks, since many newbies tend to harvest too early. Or, you could share a photo of your crop on a forum and ask more experienced growers to weigh in.

Johnson notes that the outdoor grow season lasts from around April to October, meaning if you plant seeds now, they’d still yield flower, but not much. Since it’s late in the season, he suggests buying a large clone, which will have more branches and therefore yield more flower.

Upkeep.

There are different harvesting methods, but Johnson cuts the whole plant at the base and hangs it upside down with some twine in a dark room at a temperature of around 70 degrees Fahrenheit. Add a fan for airflow — you definitely don’t want the room to be humid, which will cause mold to grow, rendering your crop unusable. It’ll probably take around a week to dry.

Don’t go overboard, though, he warns. Start with growing three plants in five-gallon pots. This way, if one dies, you’ll still have two plants, and the pots will limit their growth. A general rule of thumb is that they’ll grow one foot for every gallon of soil. He recommends mixing your own organic soil, which he explains how to do on his website and will save you the headache of adding nutrients or pH testing. “The soil is what we call alive,” he says. “It’s always breaking things down to replenish nutrients that are missing.” But if you can’t mix your own soil, or don’t feel like it, you could buy organic Pro-Mix soil, which Johnson says many outdoor growers use.

Whatever you do, don’t plant your clones in the ground. They’ll run rampant, and “you’ll have pounds of weed in your house,” Johnson says, recalling the trays of weed atop his kitchen table when his crop grew wild. “You don’t need the stress of plants getting out of control, growing over your fence.” If your neighbors can see them, they might complain about them, and having too many plants could get you arrested.

Do your homework and read up on the laws in your state. Some states prohibit growing cannabis, while others, like my home state of California, permits anyone over age 21 to grow cannabis, but only up to a certain number of plants. NORML has a pretty in-depth guide to the laws in each state. Colorado, Oregon, Nevada, Vermont, and Maine also allow cultivation, but again, the specifics depend on the state. Definitely clarify what your rights are before you start the glorious path to at-home bud gardening.

Planting.

If you use organic soil, all you’ll really need to do is add water, Johnson says — but don’t overdo it. The number one mistake he sees new growers make is watering their plants too often. In general, “watering every day is too much. The rule is, if you pick up your plant, and the pot is heavy, then it has a enough water. If it’s light, it’s dry, then you need to water.” You could also stick your finger knuckle-deep into the soil; if it feels dry, add water.

If you buy seeds from a seed bank, look for those labeled “feminized” to ensure they give rise to female plants, Johnson says. But if you’re a total newbie, he suggests buying clones, which are cuttings from a “mother” female plant, available at some dispensaries, as well as at nurseries. Not only are they easier to obtain, “they’re easier to grow. You get a clone, and you transplant it to some soil.”

Once you’ve cured your cannabis, sprinkle some bud in a bowl, or whatever your preferred method of imbibing might be, and savor your hard-earned crop.

For most first-time gardeners, we recommend buying a quality potting soil that will provide your plants with enough nutrients to get them through most of their growth cycle without having to add many amendments or liquid nutrients. This pre-fertilized soil—often referred to as “super-soil”—that can grow cannabis plants from start to finish without any added nutrients if used correctly.

Odor becomes much more difficult to manage in the final six weeks of a marijuana plant’s life, when trichomes and terpene production ramps up. You can also get odor-absorbing gels, which replace weed smells with other scents. Keep in mind that odor gels don’t eliminate odors, but simply mask them.

Fans are a must in a grow space to move air around, so buy some of those before an AC unit. If you find that fans aren’t bringing down the temperature enough, then you may want to invest in an AC.

The flowering stage will always take about eight weeks—some strains take seven, some nine, some even more, it depends on the strain.

You can let your plants get as big as you want, and can control when they flower and when you harvest, and you can start another batch right away or whenever you want. You can grow any time of year, even straight through winter or summer, and you’ll get consistent crops each time.

Finding the right soil for cannabis.

If you’re growing in a cold, wet basement, you might have to run a dehumidifier or heater to stabilize the environment. Conversely, if your space is too hot, you might need to add extra fans or an AC to cool the plants down.

Growing weed indoors is great because you can grow it any time of year and you’ll have complete control over the plant and what you put into it. Live in an apartment or a small house? Don’t worry, you can grow weed practically anywhere, even if you don’t have a backyard or a lot of extra space.

Proper air circulation will help maintain temperature and humidity, and also bring down odor. Ideally, air needs to move through a garden every few minutes, and you should create a vent to the outside. Oscillating fans, and intake and exhaust fans can move air through your garden quickly, taking odors out with them.

Carbon filters usually work best when positioned at the highest point in your grow space, where the most heat accumulates.

As your indoor weed plants grow, they’ll need less attention, but you’ll still need to check up on them every 2-3 days.

If you can’t afford both MH and HPS bulbs, start with HPS as they deliver more light per watt. Magnetic ballasts are cheaper than digital ballasts, but run hotter, are less efficient, and harder on your bulbs. Digital ballasts are generally a better option, but are more expensive. Beware of cheap digital ballasts, as they are often not well shielded and can create electromagnetic interference that will affect radio and WiFi signals.

These come in different shapes and sizes and are a great way to get rid of odor in an indoor weed grow. Also known as “carbon scrubbers” for their ability to get contaminants out of the air, these employ activated and highly ionized carbon to attract particulates responsible for carrying odor, such as dust, hair, mold spores, and volatile organic compounds, and traps them in a filter.

Many growers will start plants in a one-gallon pot and then transplant up to a bigger pot as plants get bigger. A lot of growers will transplant once, from a one-gallon to a five-gallon pot, and harvest from there. If your plants get bigger, they may need a seven- or ten-gallon pot.

Unless you’re growing in a large, open space with a lot of ventilation, you’ll need air-cooled reflector hoods to mount your lamps in, as HID bulbs produce a lot of heat. This requires ducting and exhaust fans, which will increase your initial cost but make controlling temperature in your grow room much easier.

Make sure air is circulating through your garden.

Here are some ways to mitigate odor when growing weed indoors.

When starting with clones or seedlings, you’ll want to check your plants every day because they’re delicate and sensitive to environmental conditions. You may need to adjust temperature and humidity levels in your indoor grow space at first to hit the sweet spot for your plants.

Although you’ll be controlling the climate inside the grow space, climate outside the grow space will affect your plants. If the environment outside your grow space is very warm or humid, you’ll have issues controlling your grow space. Choose a cool, dry area with ready access to fresh air from outside.

Light emitting diode (LED) technology has been around for a while, and they are getting more efficient all the time. The main drawback to LED grow lights is their cost: well-designed fixtures can cost 10 times what a comparable HID setup would.

Standard plastic containers are a popular option for growers operating on a budget. These pots are inexpensive and provide the essentials for your plants.

There should be a comfortable airflow both above and below the canopy, and fans shouldn’t blow air directly onto plants—this can cause wind burn, which makes leaves recede into a claw-like deformation.

Dehumidifiers and ACs.

Controlling temperature in your indoor grow room or cannabis garden can be achieved by manipulating these factors:

So when growing weed indoors, you can control the size of your plants by flipping them into flower whenever you think they’re big enough in the vegetative stage.

That’s a big variance, but it really depends on how big you want your plants and how often you want to harvest—you can have multiple harvests of smaller plants, or less harvests of bigger plants.

Inevitably, there will be fluctuations of temperature and humidity in your cannabis garden. These fluctuations can occur both throughout a grow space as well as within pockets inside a given room. They can also occur at different points within a given day or throughout a season as conditions change in the environment outside your grow space.

It’s a good idea to start small—the smaller the grow, the less expensive it is to set up. Newbie mistakes will be less costly if you only have a handful of plants. Additionally, most state laws only allow for growing six plants, but some allow up to 12.

One trick to avoid hot temps is to have the grow lights on during the evening, when it’s cooler outside, and leave the lights off during the day when it’s hot. This may help bring down the temps, but you’ll only be able to work on the plants at nighttime when the lights are on.

You’ll need to ensure that temperatures remain within a comfortable range for your plants, between 70-85°F when lights are on and between 58-70°F when off. Some varieties of cannabis—generally indicas—prefer the colder side of the range, while others—typically sativas—are more tolerant of high temperatures.

One sign of progress is that cannabis products can be recalled when they fail testing, just like other medical or consumer items. In December 2016 and January 2017, Organigram had to recall some of its products when residues from pesticides not approved for use in cannabis were detected. Although the company’s reputation took a short-term hit, Purcell says that recalls are a sign of the industry’s growing professionalism. Consumers can be confident that cannabis goods have been made “under a controlled, regulated environment and tested in a certified lab that guarantees safety and quality”.

In the United Kingdom, for example, strict rules concerning THC levels in medical cannabis mean that labs can find it difficult to get the sample analytical standards that they need for comparing products. The licences required to handle the standards are the same as those needed by a lab doing research on the drug itself. “It’s ludicrous that analytical standards are so tightly controlled,” says James. “The cannabis products are treated the same as a kilo of cocaine.”

“For a product to be sold in most US states, it has to be tested externally,” says Jahan Marcu, director of experimental pharmacology and behavioral research at the International Research Center on Cannabis and Mental Health in New York City.

But other issues are unique to cannabis production. And achieving the most efficient production requires growers to do research under controlled conditions to understand how both plant genetics and growing conditions can affect the product.

Many of the challenges of large-scale cannabis production can be solved by drawing on the experience of the commercial greenhouse industry, says Zheng. Growing crops commercially requires a homogenous soil and consistent irrigation. Small variations can mean that parts of the crop dry out at different rates, which leads to the spread of pathogenic agents and root rot, and to an inconsistent product. But the tomato industry, for example, has experience of growing tens to hundreds of hectares of produce at a time, and that expertise can be transferred easily to cannabis growers, says Zheng.

Testing, testing.

For years, the popular image of cannabis growers has been scruffy hippies getting high on their own supply in a disorganized underground economy, rather than shiny white industrial agriculture facilities. Even larger-scale operations involved minimal quality control or lacked formal record keeping.

“As the industry has gotten bigger, they realized they must transition to use modern horticultural science,” says Youbin Zheng, a horticulture researcher at the University of Guelph, Canada, who works with cannabis companies.

Nature 572 , S10-S11 (2019)

As the cannabis industry expands, the role of good science within it will also expand, and there will be further opportunities for collaboration. “More and more,” says Zheng, “the scientific community and industry are directly communicating and sharing information.”

Independent testing labs have sprung up to help growers to meet the requirements, but like the wider cannabis industry, they face growing pains. “At the moment it’s a bit like the Wild West, with different rules in different places,” says Andrew James, marketing director of Ellutia in Ely, UK, which makes chemical analysis equipment for the cannabis industry, among other markets. “It can be hard to know what to test for, how to test and where to do it.”

Brian Owens is a freelance journalist in St Stephen, New Brunswick, Canada.

A student inspects a cannabis plant at Niagara College Canada’s teaching laboratory in Niagara-on-the-Lake, Canada. Credit: Niagara College.

“Because of the federal strictures, there weren’t any standardized methods. Labs had to validate everything themselves,” Brauninger says. “It’s difficult to bring in expertise when there isn’t a wealth of information available, and no trade association to help share techniques.”

Besides the challenges of growing a sufficient amount of high-quality cannabis for a rapidly growing market, cannabis companies have to deal with something that illegal growers do not — government regulation.

Part of Nature Outlook: Cannabis.

Cannabis analytical labs are becoming more professional. “I’ve seen an evolution in the sophistication of the industry,” Brauninger says. “Most of the people running labs now have PhDs and experience in the pharmaceutical industry. It’s light years more sophisticated than five or six years ago.”

More from Nature Outlooks.

Although small-scale growers of illicit cannabis can get away with vague descriptions of strains and considerable variation between batches, commercial producers have to meet the same standards as they would for other consumer products. They need to produce a reliable product and follow the stringent rules and regulations that apply to product labelling and safety in their country.

But as legal medical — and increasingly, recreational — cannabis becomes more widespread, the cannabis industry is becoming more professional. By adopting the methods and rigour of plant science and analytical chemistry, it is ensuring that it can produce safe, consistent and high-quality products for a fast-growing and lucrative market.

In Canada, government regulations require producers to use an independent lab to measure the level of cannabinoid in dried cannabis flowers and oils so that the resulting products can be labelled appropriately. Producers must also test for contaminants such as the bacterium Escherichia coli , mould, heavy metals and 96 types of pesticide. When edible cannabis products become legal in Canada later this year, they will face similarly stringent rules, says Purcell; labels on such products will have to convey the same nutritional information as do those on any other food product. In the United States, the regulations are broadly similar to those in Canada. But each US state where medical or recreational cannabis is legal sets its own testing regime — and those requirements can vary widely and change quickly. “In Delaware, the regulations are now totally different than two years ago,” says Marcu.

That led to labs being set up quickly with old equipment in unsuitable spaces, and with minimal quality control. James says that, in the past, it was not uncommon to meet people at trade shows who had bought analytical kits on the online auction site eBay and were running testing labs from their bedrooms.

Although many small-scale cannabis growers at first questioned the need for intensive product testing, most can now appreciate the benefits that the rules bring to the market. “People see the need for quality control and testing,” says James. “It brings a legitimacy to the industry that hasn’t always been there.”

To run these advanced facilities, cannabis companies need researchers who are experienced in plant science, microbiology, chemistry and other scientific disciplines — and they are turning to academia to find them. “Instead of underground growers, they are hiring lots of university-educated and trained people,” says Zheng.

A commercial medical-cannabis cultivation facility in Moncton, Canada. Credit: Organigram Inc.

And not all analytical labs are up to the job. Roger Brauninger, biosafety programme manager at the American Association for Laboratory Accreditation (A2LA), a non-profit organization in Frederick, Maryland, says that although US states introduced requirements for external testing as medical or recreational cannabis became legalized, there was rarely any infrastructure or expertise in place to facilitate a professional testing regime. Even the most established labs, located in California, have only been around since the mid-2000s — despite the state legalizing the medical use of cannabis in 1996.

Organigram’s operation is in stark contrast to the image of an illicit farm hidden in the woods. It is entirely indoors, with 52 identical growing rooms on three floors. Plants are propagated by cloning, rather than grown from seed, so the crop’s genetic identity remains the same from generation to generation. The growers track and log all growing parameters, and then tweak them as needed to maintain consistency. Purcell sees the company’s operation as a ‘manufacturing facility’, rather than a garden or a greenhouse. “There are quality checks like you would see in any manufacturing facility, whether it was producing food or tyres,” he says.

Zheng’s laboratory is one of many that are working with cannabis producers to support and guide this effort. He is studying how the amount and wavelength of light used in growing can affect the plant’s cannabinoid composition. Increasing the amount of ultraviolet light, for example, can increase levels of tetrahydrocannabinol (THC), the main psychoactive component of cannabis. “We want to create a lighting recipe which will help producers get a consistent product,” he says.

“Cannabis is just another crop,” he says. “The commercial flower and vegetable industries have been working on the same problems for many years, and they have the technology already.”

Cannabis companies are quickly adopting techniques and technologies that were pioneered by commercial agriculture and horticulturalists. Organigram, a cannabis producer in Moncton, Canada, stringently controls its growing operations, says Jeff Purcell, vice-president of operations. “The growing environment is standardized, and we have full control over the air, light, temperature and fertilizer,” he says. “It’s all highly automated and computer controlled.”

The large-scale, controlled environment enables Organigram to conduct systematic, controlled trials and to produce huge amounts of data — with 5 cycles of growth per year in each of the growing rooms, it can generate more than 250 generations’ worth of growing data each year, says Purcell. The company can use those data to determine what works best for the plants, and then replicate those conditions at scale. “That’s the big difference with the black market,” he says. “When you scale up, you have to take a data-driven approach.”