Uniformity in Cannabis Cultivation

Written by Kaisha-Dyan McMillan & Tyler Simmons

Growers who use crop steering techniques are relying upon the plant’s cues to make informed decisions about water, light, and climate that will ultimately produce the outcomes they’re looking to achieve. And because having to manage substrate differences, overall environment, and other variables in the garden can impact growers’ ability to achieve the results they want, getting a handle on uniformity is crucial.

Growing cannabis in a controlled environment puts cultivators in the position of having to create the optimal set of conditions for their plants to live, achieve certain traits, and produce enough biomass to fulfill particular yields. But unless growers are applying the same baseline of conditions for each cultivar all the way down to the individual plant level, crop steering success can be hard to come by. That’s where uniformity comes in: ensuring conditions are uniform between each plant makes crop steering easier and can lead to replicable quality, more projectible yields, and continuous improvements with every harvest.

The 3 Pillars of Uniformity

According to Cultivation Consultant Tyler Simmons, growers who focus on what he calls the Three Pillars of Uniformity – in the substrate, the climate, and with each plant – will see the most benefit. “Those three pillars are holding up the outcome that we're looking for,” he says, “and they cash out as improved uniformity in terms of the total number of flower sites per cubic foot of canopy above a minimum PPFD level.”

Substrate Uniformity

“There's a lot of ways of interpreting what crop uniformity means and also a lot of different places where it's relevant within the cultivation process,” Tyler explains. Substrate uniformity is all about “the root zone,” he says, adding that for growers this means, “making sure that each plant has the same substrate volume, the initial soaking and conditioning process is the same, that the drip system is uniform so that plants are always receiving the same amount of nutrients and water.” 

Not only are there variations between substrates – the grower using coco is dealing with a set of conditions very different from the one that’s cultivating in Rockwool – but also within the individual substrates themselves. One way this shows up is when EC readings vary from one coco bag to another despite being produced by the same vendor. By not factoring this variance into the initial soil and conditioning process, for example, growers could wind up with substrate volumes that come out differently for each plant. 

Irrigation strategy and equipment can also impact substrate uniformity. A clogged emitter or multiple missed P2 shots are more than just maintenance issues; they’re a signal that one or more of your plants is not being watered properly. Leaving substrate and irrigation variances unchecked for too long could affect everything from nutrient uptake and overall plant growth to yield.

Tyler also advises growers to make sure “that the sensor placement is consistent so that your data is also uniform.”  Crop registration, a practice in which cultivators regularly log data as a way of measuring their plants’ productivity, goes a long way to inform the decisions they make when crop steering. But when substrate sensors are moved from one pot to another, or positioned inconsistently – on the drain side of one pot versus further away from the drain of another, for example – readings are unpredictable, which means you won’t get an accurate picture from the data.

Climate Uniformity

Cultivating in a controlled environment places growers in the driver’s seat of having to monitor and adjust conditions to facilitate the outcomes they’re hoping to achieve with their plants. That’s why it’s important to hone in on the second pillar of climate uniformity, which Tyler describes as, “just having uniformity of plant climate across the room [and] would encompass lighting intensity; air movement and temperature, humidity, VPD.”

A plant positioned at the center of the room isn’t growing under the same conditions as the plant located near a fan. The temperature difference alone is going to have an impact, and the grower managing both plants must find ways to create a more uniform environment by minimizing this variance.

Plant Uniformity

If dialing in substrate and climate uniformity before the next harvest sets a great foundation, the third pillar of plant uniformity brings it all home. 

Plant uniformity comes down to “basically two parts,” Tyler says. “Having clones that are of equal health and size when they're created, then either monocropping so that the strains all have similar architecture. Or strain matching so that if you're running more than one strain, they at least have similar growth characteristics and structure.” 

Growers working with mixed cultivar crops can learn a lot from documenting what’s going on with their plants: the way each cultivar grows in response to a particular irrigation schedule, how yields were with every cycle, and more. This documentation can then be used to group similar-growing plants together, and allow growers to apply crop steering techniques that can improve each of the different cultivars.

A plant’s needs change with every growth phase, and every cultivar is different. Monocropping and strain-matching help growers focus their time and effort on plants with similar traits, ensuring even plant heights and consistent yields in the long run.

In Summary...

• Setting uniform conditions within the substrate, climate, and with each cultivar makes crop steering easier and can lead to replicable quality, more projectible yields, and continuous improvements. 
• Substrate uniformity means each plant has the same substrate volume, initial soaking and conditioning is the same, and irrigation is the same. Proper sensor placement helps ensure the data from the substrate is accurate.
• Minimizing variances in lighting intensity, air movement, temperature, humidity, and VPD creates climate uniformity.
• Plant uniformity comes down to growing strains of equal health and size together (monocropping), or cultivating different strains with similar growth characteristics and structure together (strain matching).
• Together these cash out as improved uniformity in terms of the total number of flower sites per cubic foot of canopy above a minimum PPFD level.