The lines separating food and cannabis cultivation methodology have slowly begun to blur. Leafy greens and lettuce producers in controlled environments have long-utilized multi-tier cultivation rooms. Now, this trend is starting to gain some traction in cannabis cultivation as well. In the endless quest to improve efficiencies and boost yields, multi-level cultivation environments have the obvious benefit of allowing for more production and higher yields within the same square footage. However, there are also some drawbacks. Carefully consider the benefits and risks of cultivating in multiple levels prior to facility construction.
For comparison, leafy greens are relatively short plants. They have limited height requirements, so you can accommodate multiple tiers even within relatively low overall heights. Once planted, most leafy green varieties require very little direct interference other than periodic inspection and their automated irrigation systems. Conversely, depending on the time spent in veg and cultivation methodologies, mature cannabis plants are generally three to six times the height of ready-to-harvest leafy greens. Cannabis plants also require frequent direct interference related to trellising and pruning. This means you must take the accessibility of higher levels into account to avoid compromising operational efficiencies. Both factors make multi-tier gardening simpler and more feasible for widespread adoption in leafy green production than in cannabis production. However, that doesn’t mean it shouldn’t be considered in certain circumstances.
Lighting and vertical space requirements
Lighting technology and selection will directly impact the ceiling height and upper-level access requirements of a multi-tiered facility. Depending on the desired lighting densities and the specific fixtures in use, this could mean adding significant vertical space requirements to a stacked grow. For instance, HID fixtures will typically require at least 24-inches, more commonly 48-inches, and sometimes as much as 72-inches of clearance from the top of the canopy to the bottom of the light fixture. On the other hand, you can typically mount LED fixtures much closer to the canopy—in some cases only a few inches. This is because most LED fixtures produce a more collimated light and less radiant heat than their HID counterparts. When LED’s are in use, double stacking cultivation spaces requires less vertical space than HID lighting. Additionally, access to upper levels is far more convenient.
Multi-level irrigation design: an uphill battle
Irrigation design is another variable to take into consideration when planning a multi-tier facility. Pump performance decreases as vertical flow requirements (lift) increases, so this must be taken into account within the irrigation design. Access to sprayers and drip heads for maintenance is also important. Assume that you’ll need access to each plant in the room on any given day of its growth cycle to ensure that you can properly maintain not just the plants, but every irrigation and trellising component as well.
Homogeneous environments in multi-tiered facilities
Perhaps most important, as it’s extremely difficult to correct in an active cultivation environment, is the HVAC design. Without proper airflow patterns, every cultivation facility is prone to temperature and humidity fluctuations from zone to zone. Multi-tiered designs are especially vulnerable to stagnation within each layer due to the vertical and horizontal interference with airflow created by having multiple layers.
Because supply air from HVAC systems comes out far colder and dryer than the room’s setpoints, it’s not as simple as just pointing some HVAC supply air into a row of plants. The supply air from the HVAC system must be correctly mixed with room air to obtain a homogeneous temperature and humidity. Then that air is supplied to the canopy. In addition, be sure to design the velocity and direction of the airflow with care. Too little velocity will fail to deliver the air to every plant in each row. Too much will force rapid transpiration and other crop damage.
If you’re considering a multi-tiered design, it’s in your best interests to work with an HVAC designer who has experience with these types of configurations.
When does multi-level cultivation make sense?
Consider that when building a cultivation facility, the real estate itself (square footage) in most circumstances is only a fraction of the overall build-out budget. Outfitting the space with infrastructure suitable for cultivation is where the bulk of the expense lies. This is why multi-tiered cultivation is rarely a more budget-friendly option than single-tiered cultivation. Although areas where square footage is at a high premium are sometimes an exception. In the current industry environment, we most often see cultivators who opt for multi-tiered cultivation do so in vegetative rooms. Here, they’re more comfortable with lower wattage lighting technologies and plants are shorter and don’t yet require trellising. This provides a happy medium where they can increase the overall flowering canopy within a given space while limiting the challenges associated with layered facilities.
Despite the challenges of cultivating indoors in multi-level environments, if each element is considered and addressed at the design level, it may be a good option even in flower.