Maximizing Yields with Indoor Cannabis Cultivation

With that control comes the ability to plan for and achieve certain outcomes. In this article, we’ll explore what cultivators should keep in mind when maximizing yields with indoor cannabis cultivation is the goal.

Setting optimal environmental & substrate conditions

Growers who steer their crops rely on their plants’ vegetative and generative cues to make decisions that ideally produce certain outcomes. The goal of maximizing yields essentially comes down to cultivators needing to find a balance that allows them to maintain healthy plants while steering them toward producing as much biomass as possible with every harvest. That means growers must ensure the conditions within the overall environment are optimal for every cultivar throughout each growth phase. And when it comes to maximizing yields, getting a handle on ambient air temperature is key.

The best temperature for indoor weed plants changes with each growth phase, but should always be within a range that promotes good plant growth and allows the cultivator to steer the crop. Plants aren’t the only things inside a grow room. They share space with lights, fans, air conditioners, dehumidifiers, and other equipment, plus humans from time to time – and each of these elements produces heat that increases the temperature and humidity in a room. The challenge for growers therefore is figuring out how to consistently keep a balanced environment while also managing fluctuations that can occur when equipment is constantly cycling on and off.

Ultimately, everything that a grower does to manipulate their environment impacts the amount of light that hits each plant. Lighting alone can significantly impact a room’s heat and humidity levels. HPS lights, for example, transmit enough radiant heat during the daytime to significantly warm the plants. LEDs on the other hand don’t produce as much heat as HPS lights. So while leaf surface temperatures don’t get as hot, a grower may need to run their LEDs hotter at certain growth phases as a result. Tied to lighting is the amount of CO2: indoor grow operations benefit most when CO2 is 250 ppm above the amount of micromoles of light at the canopy.

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. Optimal VPD ranges allow 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. Operating outside that range can lead to lost time and production, that’s why climate sensors are invaluable tools that help growers keep their environmental conditions in check on a consistent basis.

Some of the practices that growers have become accustomed to may need to be adjusted when steering plants toward higher yields. Using a 5-7 gallon pot for one plant and hand watering it every day is a great way to achieve quality, but that process may not work at-scale – lots of labor is needed to move big pots like that around, and that costs time and money. Not only that, but a larger pot won’t dry back fast enough to support a more vegetative irrigation strategy because it holds too much water. But indoor cannabis growing systems that utilize smaller pot sizes, say 1 gallon, combined with a reliable drip irrigation system can accommodate the more frequent waterings that produce faster drybacks and encourage the plant to grow. So to start, rooting into a well-balanced plant-to-substrate size allows the plant to achieve a consistent and fairly deep dryback that facilitates a grower’s ability to steer it toward maximum production.

From there, growers must determine the best substrate for their production needs. Opting for a substrate with a high water holding capacity provides a good balance between delivering a significant dryback consistently, and maintaining enough irrigation to keep everyone on the team from accidentally watering the plants too much. A 1-2 gallon coco pot or 4-inch Rockwool cubes on top of 36-inch slabs are good media sizes that can help growers achieve this sweet spot.

Dialing it all in to optimize yields

In order to put these various levers in motion, each grow room must be capable of hitting all the necessary marks throughout each growth phase. From ensuring proper substrate and climate sensor placement; to checking that dehumidification, air conditioning, and all equipment is in good working order; to setting the parameters within the controls systems used to run that equipment, and more – everything must be working in proper alignment with the individual needs of each plant. 

Once room conditions are established and under control, it’s time to break the flower cycle into three phases. During each phase, growers must be prepared to make significant changes in both their environmental and irrigation strategies:

• Generative phase typically lasts 3 weeks. This phase calls for higher temperatures, slightly higher humidity, lower VPD, and fewer feeds.

• Bulking phase lasts around 3-4 weeks. During this phase temperatures and humidity should be lowered slightly, a small day/night temperature differential should be introduced, a slightly higher VPD (1.2-1.4 range), and more frequent irrigation.

• Ripening phase generally lasts 1-2 weeks. In this phase, daytime temperatures should differ from night temperatures by roughly 10 degrees (75℉ in the day shifts to 65℉ at night, for example), the humidity is lowered to maintain optimal VPD range, and irrigations occur less frequently.

Production guidelines will vary for each strain, but this basic outline gets growers accustomed to optimizing each phase of the plant’s life cycle. Rather than trying to force the plant to do certain things by creating stress, the grower is responding to the plant’s cues in ways that optimize each phase of growth toward particular outcomes – including improved yields.

In Summary:

• To maximize yields, growers must find a balance between keeping plants healthy and steering them to produce as much biomass as possible. 
• Dialing in ambient air temperature and choosing the proper pot size and substrate for production sets a framework for growers to consistently optimize environment and substrate conditions.
• Breaking the flower cycle into three phases – generative, bulking, and ripening – offers growers an outline for optimizing each phase of plant growth towards better yields.