Page 20 - Griffin Gazette - October 2026

STEER YOUR CANNABIS CROP

from the Root Up

By Tanner Bailey, GGSPro Technical Services Supervisor;
George Grant, Ph.D., GGSPro Technical Services Manager

The strategy of “crop steering” gets plenty of attention in controlled-environment cannabis
production. There is much grower discussion about irrigation timing, dry back percentages,
frequency vs. volume, starting and leachate water electrical conductivity (EC), lighting intensity and
regime, vapor-pressure deficit (VPD), and whether the crop needs more vegetative or generative
push. All of those factors matter, but the ability to crop steer reliably begins before the first irrigation
event is scheduled. It starts with the substrate. The growing media determines how much water
the root zone can hold, how quickly it drains, how much oxygen remains available, and how rapidly
conditions change between irrigation events. Irrigation may be the steering wheel, but the substrate
determines how responsive the crop will be to input or cultural changes and allows growers to
impart these changes with more confidence and control.

WHAT ARE WE TRYING TO STEER?

Crop steering uses irrigation and environmental adjustments to influence plant growth. A vegetative
strategy generally supports leaf, stem, and root development. A generative strategy encourages
the plant to shift more energy toward flower development and maturation. Irrigation is one of the
primary tools used to create these responses. Frequent irrigation events with smaller volumes, along
with smaller/shorter dry backs, generally support optimized vegetative growth. In contrast, fewer
irrigation events with larger dry backs, accompanied by large volumes (i.e., to container capacity)
when feeding, can create a stronger generative response.
The challenge is applying these concepts across an entire commercial facility. Container volume,
plant size, root development, substrate structure, emitter output, lighting, temperature, humidity,
and of course, strain variation in vigor/feed requirements all affect the result. It’s a balancing act, so
try to find ways to increase flexibility without compromising the end product. Choosing a growing
medium that provides this balance is what growers seek and hold onto once they have found it. A
20% dry back in one substrate may not create the same root-zone conditions as a 20% dry back in
another. Growers cannot build a successful crop-steering program around percentages alone. They
must first understand how their chosen substrate holds, distributes, and releases water.

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