The Ultimate Guide to Indoor Cannabis Cultivation:
Tips, Techniques, and Best Practices

And whether a grow is in a closet, a basement, or spanning thousands of square feet of indoor space, lots of planning and preparation must be done well before the first seed or clone gets planted.

In this article, we’ll explore the following:

• Setting Up Your Indoor Cannabis Grow Room
• Choosing the Right Cannabis Strains for Indoor Cultivation
• Cannabis Growing Mediums and Nutrients
• Germination, Vegetative, and Flowering Stages of Cannabis Growth
• Pests and Diseases: Prevention and Treatment
• Harvesting, Drying, and Curing Your Cannabis

Setting Up Your Indoor Cannabis Grow Room

A well-designed indoor grow room should allow the cultivator to nurture each plant’s ability to grow to its fullest potential. This starts with selecting the right grow room location and making sure the space is set up for optimal workflow. In indoor or greenhouse environments, cultivators must constantly manage light, water, temperature, CO2, and humidity in ways that align with their objectives. Part of choosing a location requires figuring out how to keep the outdoor environment from inhibiting the team’s ability to manage indoor temperature and humidity at every phase of plant growth. That’s why before build-out begins, understanding the impact a region’s weather and climate conditions may have on a facility’s indoor environment is so crucial – outside conditions directly influence a range of decisions including how to approach lighting, and to what degree the space needs air conditioners, dehumidifiers, and other industrial equipment.

Cannabis, like all plants, needs light to survive. And in greenhouse and indoor spaces where access to sunlight is limited or unavailable, choosing the right artificial lighting is a critical first step when setting up a grow room. Since light intensity has a direct relationship with the plant’s ability to uptake CO2, photosynthetic photon flux density or PPFD – which defines the amount of photosynthetically active photos that reach the plant every second – is a great reference point to keep in mind when exploring lighting options which, for most growers, comes down to two categories: HPS or LEDs. HPS bulbs in the 600-1000 watt range have been a standard in indoor grows for decades. While largely considered old-school tech, HPS lights produce radiant heat and emit a spectrum that supports the overall temperature of each plant and can also boost anthocyanin production. But because their technology is out-of-date, HPS bulbs have the potential to become fire hazards when they burn out and they’re nearly obsolete, which makes HPS bulbs expensive and difficult to find. One reason for this market shift is the growing popularity of LEDs, which are less expensive and more energy-efficient than their vintage counterparts. But while LEDs typically produce less heat than HPS bulbs, growers may have to increase dehumidification capacity in response.

Another consideration for indoor and greenhouse growers is how to manage temperature and humidity to ensure plants stay healthy. Air flow must be optimal to support transpiration rates, so when a room is overcrowded, plants have to work much harder to take in water, light, and nutrients. Not only that, such conditions can also aid the spread of powdery mildew and other pathogens, pests, and molds. That’s why in addition to bringing in good quality filters for clean ventilation and fans to keep air circulating, cultivators must be prepared to mitigate the heat produced by lights and other industrial equipment that can impact the environmental conditions in a room.

Once an indoor garden is filled with plants, people, and the necessary equipment, the challenge becomes figuring out how to control temperature and humidity at all phases of plant growth. In early growth stages, adding humidity to the room may be necessary, but growers may need to remove humidity as more biomass is produced. Since tracking and monitoring vapor pressure deficit or VPD – which measures the current moisture in the air compared to its saturation point – is the most efficient way to keep heat and humidity levels in balance, growers can also use VPD to guide their decisions about dehumidifiers, air conditioners, and other equipment that can help them manage airflow and humidity. 

Choosing the Right Cannabis Strains for Indoor Cultivation

While advances in genetics and an evolving consumer landscape have led the industry to start spotlighting terpene and cannabinoid profiles, the traditional indica-sativa distinctions are still largely part of the lexicon for growers. When it comes to physical strain characteristics, indica plants are typically known to be shorter and bulkier, and sativa plants are generally considered to be taller and lankier. Cannabinoid profiles for indica strains tend to include CBD, while sativas are generally known to be higher in THC/THCA and lower in other cannabinoids. Since hybrid strains exist somewhere in between, everything from their physical characteristics to cannabinoid and terpene profiles is highly variable. But regardless of how we generalize physical strain characteristics, the biggest considerations - especially for commercial cultivators - are how long it takes a plant to flower, the amount it yields, and its resulting product quality. 

Striving for ideal strain characteristics begins with cultivators first deciding how large they want their plants to be. Setting up a small grow room with double-stacked plants is an efficient way to use limited space, but this will result in shorter plants which can result in smaller yields. A massive room filled with hundreds of plants in 1-gallon pots will likely yield much taller plants, but managing them will be far more labor-intensive. Substrate media is another consideration, as choosing between coco coir and Rockwool involves determining which can achieve the drybacks that will lead toward desired outcomes. And the amount of time it takes for plants to mature – with indicas generally taking 47-60 days versus 60-80 days for most sativas – means cultivators must also consider how flowering time will ultimately impact their production schedule.

Indoor gardens offer growers more control, enabling them to set optimal substrate and environmental conditions for each cultivar throughout every growth phase. And getting a handle on ambient air temperature is crucial for growers looking to maximize yields. Dialing in optimal VPD ranges allows for the most efficient movement of water through the plant, facilitating plant growth while also minimizing the potential for mold – especially crucial when trying to maximize yields. And because operating outside that range can lead to lost time and production, climate sensors are invaluable tools that help growers keep their environmental conditions in check with every run.

But before growers can get there, they must be sure they’re set up for success with the best quality seeds and clones. Buying seeds from a reliable resource and choosing stable cultivars with the most desirable traits will likely have more positive results than planting seeds purchased from a random website and hoping for the best. Working with reputable breeders not only ensures access to better quality seeds; it also gives growers a direct line of communication with someone who understands the lineage and can offer cultivation advice based on actual strain genetics. After identifying their best resource for seeds, growers have other business decisions to make including choosing between standard versus feminized seeds, whether the seeds are for pheno-hunting or breeding purposes, and if the strategy to protect quality includes grouping strains with similar traits in the same room through a process known as monocropping.  

When selecting clones, growers who pop seeds for pheno hunting have the perfect resource: their own plants. Cultivators who go one or two generations into cloning are able to see differences between those generations, and may not get the yields they expected to see with the original seedling. Opting instead to sprout seedlings until they are around 18 inches tall or so, cutting and flowering a clone or two directly from those plants, and then taking the seedling out of rotation can help growers get a true evaluation of how well that cultivator will perform at their facility. 

Cannabis Growing Mediums and Nutrients

Since the ability to manage substrate and environmental conditions is a huge benefit of cultivating indoors, choosing the right grow medium is crucial. 

Soil is a complex, organic medium filled with living organisms that actively process nutrients within conditions and timelines that outdoor plants adapt to naturally. Growers who understand soil biology are best able to maximize their outputs in an indoor environment using this medium, but not being able to control variables is the main reason why soil is usually not the first choice for indoor commercial cultivators. The same is true for cultivating with aeroponics, a system that keeps roots exposed and relies upon mist to deliver nutrients. While there’s hardly any medium to manage with aeroponics, there’s also zero buffering capacity in the event of water or power loss. Plus, changes in nutrient composition can immediately impact plant health if they’re not addressed quickly in aeroponic gardens. This is why producers commonly choose soilless media like Rockwool and coco coir for their indoor gardens. Not only do they require fairly consistent irrigation and allow growers to adjust root zone conditions when necessary, but they’re also typically more forgiving and flexible to work with than either soil or aeroponics. 

Once a substrate is selected, cultivators must decide which nutrients and fertilizers will be best for their cannabis plants. Fortunately for business owners, the industry’s continued growth means cultivators have more cannabis-specific formulations to choose from than ever before. For small-scale operations, mixed nutrients are a great option, while larger grows may prefer two-part salts which can be diluted and used for fertigation. Since nutrients can add up and becaome a costly output for producers, which direction they choose ultimately comes down to such factors as how the nutrients impact energy and water usage, waste management, and labor.

Germination, Vegetative, and Flowering Stages of Cannabis Growth

Once growers have their seeds, a temperature of around 75 degrees with 70-90% humidity and 150 PPFD of light is the optimal environment to support germination. A growing tray, humidity dome, and heating mat can help create those conditions, leading seeds to pop on average within 24-36 hours. Once the first set of true leaves starts to appear, it’s time to transfer the seedling into a 4-inch pot – or a coco or Rockwool cube – and keep it in a high-humidity environment. After 7-10 days, reduce the humidity within a range of 65-70% and increase light intensity as new leaves begin to sprout. From there, maintaining ongoing sanitation practices and using clean water will go a long way to keep the seed tray and humidity dome free from bacteria. Whether planting in coco or Rockwool, using trays to germinate seeds helps growers maintain control of substrate conditions far better than they would planting directly into a larger media, as the slower water uptake could drown the seed or cause it to become infected with bacteria.

During the generative phase, which lasts about 3 weeks, plants typically need higher temperatures, slightly higher humidity, lower VPD, and fewer feeds. When plants reach the bulking phase, ideal conditions include lowering temperature and humidity slightly, raising VPD to a range of 1.2 - 1.4, introducing a small temperature differential from day to night, and more frequent irrigation for roughly 3-4 weeks. Once plants reach the 1-2 week ripening phase, daytime temperatures should hover around 10 degrees higher than nighttime temperatures, humidity is lowered to keep VPD ranges optimal, and irrigations are less frequent.

As the plants reach the vegetative stage, cultivators may choose to defoliate the weak lower leaves as they die off. As a general rule however, training and pruning plants during the vegetative stage isn’t necessary, as the goal is to allow the clones to grow as much as possible. Depending on the strain, growers may feel the need to start topping plants around day 7-10 of veg, but this practice can add a week to the veg cycle without impacting strain performance either way. The decision to train or prune ultimately depends on whether the added step leads to better yields and quality – yet another example of why documenting everything through crop registration is so important. 

When the goal is maximizing yields, there are a lot of factors to consider well before plants reach the flowering stage. Instead of choosing to hand-water plants in 5- or 10-gallon pots – which is a great way to achieve quality but difficult to scale – indoor grows that use 1-gallon or smaller pot sizes combined with a reliable drip irrigation system are better able to accommodate the more frequent waterings that encourage growth and lead to faster drybacks. Choosing a substrate with high water holding capacity right from the start gives growers the optimal balance between achieving a consistent, significant dryback and maintaining enough irrigation to prevent overwatering.

Pests and Diseases: Prevention and Treatment

Having control over an indoor environment doesn’t mean there won’t be challenges – and dealing with pests and pathogens is one of the most common issues growers will eventually have to face. From thrips, spider mites, and other pests, to fungal infections like powdery mildew and viruses like hop latent viroid, contagions come with the territory when cultivating an agricultural product and cannabis is no exception. While applying fungicides or pesticides is a surefire way to treat outbreaks, adopting integrated pest management (IPM) practices is a far more effective strategy in the long run. 

When pests or other outbreaks occur, a key troubleshooting step is figuring out how they got there in the first place. Getting to the root cause of where they came from and why they’re appearing now will help the cultivation team determine if this is a one-off situation or a sign of a much bigger problem. Checking the cleanliness of the facility is another important step, since everything from leaving organic debris lying around to taking too long to fix maintenance issues to not adhering to cross-contamination and other sanitation protocols regularly can unwittingly facilitate the spread of pests and infections. Using air conditioners and other equipment to ensure proper ventilation and manage temperature fluctuations, staying on top of biosecurity, and otherwise keeping substrate and environment conditions dialed in is a more holistic approach to keeping outbreaks from occurring in the garden.

Harvesting, Drying, and Curing Your Cannabis

The incredible diversity of physical attributes, cannabinoid profiles, and terpene expression between cultivars proves that no two strains are exactly alike – and the same is true for cultivation time. While a variety of factors including grow medium and environmental conditions influence how long it takes a cannabis plant to grow, its life cycle typically lasts about 9-12 weeks. And once harvest arrives, there’s still plenty of work to be done.

Cannabis producers that monitor relative humidity (RH) are familiar with the concept of water activity (aw), which the food industry uses references when speaking to the ratio of vapor pressure of water in a material to the vapor pressure of pure water at the same temperature. As water seeks equilibrium by moving from high pressure to low pressure in its environment, water activity measures that movement and gives growers insights into the RH percentage in their plants’ – a crucial metric for drying cannabis properly. 

When water activity is too high it can lead to fungus, yeast, and microbial growth. Water activity that’s too low can cause a reduction in terpenes and cannabinoids and result in dry, dusty buds. Both scenarios can add up to potential product recalls, negative consumer experiences, and lost profits. After all the hard work and effort cultivators put into growing healthy plants, maintaining optimal humidity levels is just as crucial in the drying and curing rooms as it is throughout the growing process – and using sensors to track and monitor moisture levels, RH, and aw will yield far more reliable results than the naked eye ever could. Then when it’s time to package the product, storing the buds below water activity limits helps keep molds and microbes at bay and preserves the aromas and flavors that keep patients and consumers coming back for more.

Cannabis Harvest Yields and Optimization

There’s a lot riding on growers’ ability to cultivate cannabis successfully in the regulated market. Being expected to achieve quality, deliver product consistency, and operate in compliance at scale with every harvest in an industry that’s heavily regulated yet lacking in centralized systems and practices takes more than gut instinct alone. 

Cultivating in an indoor or greenhouse environment allows growers more control over their plants, but that means they must create an environment that’s as close to nature as possible. This requires regularly monitoring and adjusting the lighting, irrigation, and other environmental factors in response to what the plants need. Crop steering is a practice in which cultivators manipulate light, climate, and irrigation in an indoor or greenhouse environment to encourage their plants to grow a certain way. Long used in hydroponic vegetable production, crop steering is achieved in part by adjusting the frequency and amount of irrigation specifically for the environment, cultivar, and stage of plant growth. 

To improve yields, cultivators must manage conditions within the overall environment to make them optimal for each cultivar at every growth phase. VPD is the most efficient way to balance heat and humidity levels, while using a grow medium with a high water holding capacity that can deliver a significant dryback consistently and maintain enough irrigation to prevent overwatering is ideal. The most common mistakes that lead to low yields are insufficient amounts of light and water stress during cultivation, and overdrying during the drying/curing/trimming process. Dialing this in ultimately comes down to how operators approach production as a whole.

To gauge productivity, indoor growers measure yields using the metric of grams per square foot per year. But it takes more than a skilled cultivator to get harvested plants into saleable form – here are the 3 main steps to cannabis production:

• Planning, or the process of selecting and sourcing genetics.
• Cultivation, which is growing plants to maturity.
• And Post-Harvest Processing of the salable parts of the plant into the final product.

Whether the effort put into cultivation results in revenue and profit is determined by planning and post-harvest processing. That’s why companies that recognize the importance of cannabis production are more likely to have greater profitability than those brands that rely on cultivation alone. With the help of the a production platform like AROYA, growers can use data to analyze outcomes and change controllable input metrics to improve the next harvest.

Conclusion

In Summary...

• A well-designed indoor grow room must support cultivators’ efforts to grow healthy plants, facilitate good workflow, and accommodate the necessary industrial equipment to create the optimal indoor environment while also reducing the impact of outdoor weather and climate conditions.
• Buying standard or feminized seeds from a reputable breeder who can offer cultivation advice about their lineage, sourcing clones from your own seedlings, and growing plants that exhibit optimal strain characteristics within a reasonable production timeline are key considerations when selecting the best strains to grow.
• Soilless media like coco coir and Rockwool are commonly used in indoor operations because they require fairly consistent irrigation, offer growers more control over root zone conditions, and tend to be more flexible and forgiving than soil or aeroponics. 
• During the germination, vegetative, and flowering stages growers must be prepared to adjust environmental and substrate conditions to keep plants healthy and steer them toward target outcomes.
• The best way to prevent pests and pathogens is to use a holistic approach -- by incorporating equipment to ensure optimal airflow, temperature, and humidity; adopting biosecurity and cleanliness protocols; and dialing in substrate and environment conditions.
• Water activity is a crucial metric for making sure cannabis is dried, and cured properly after harvest.
• Successfully turning harvested plants into saleable form takes Planning, Cultivation, and Post-Harvest Processing, the 3 main steps of cannabis production.