Imagine the perfect cannabis growing environment–high light intensity, precisely controlled environment, CO2-rich air, automated systems, minimal energy usage…this is the holy grail for many cannabis growers, and with advances in greenhouse technology it is one that is now within reach.
Until recently, cannabis growers faced two choices for housing a grow operation: indoor or outdoor. Outdoor growers commonly tout the higher yields and lower costs of growing at larger scales under natural light. Indoor growers swear by the added climate control afforded by an enclosed environment where light, temperature, CO2 and airflow can be controlled with the punch of a button.
As a category, greenhouses occupy a middle ground on this spectrum. However, until recently, standard greenhouse structures presented their own challenges for cannabis growers. Advances in greenhouse design and technology are changing that, allowing greenhouses to provide the best of both worlds: both natural lighting and a precisely controlled indoor environment.
Shedding Light on Traditional Greenhouses
Though artificial lights are becoming more efficient, it is still hard, if not impossible, to compete with the giant free lamp in the sky. On a clear day, indoor light levels in a greenhouse are in the range of 1,000-1,500 micromoles/m2/second. That wordy unit describes of the amount light that plants use, called PAR light, hitting a surface at a single point in time. In comparison, light intensity one meter away from a 1,000-W HPS lamp is in the range of 500-800 micromoles/m2/second. Light intensity under a 400-W HPS lamp is only 200-400 micromoles/m2/second.
In short, natural light usually dwarfs artificial lights in its intensity. It’s also full-spectrum, providing all the wavelengths plants use. But most importantly, it’s free. By not having to run lights 12-18 hours a day, greenhouse growers dramatically reduce the costs of year-round cannabis production. Though estimates vary, most analysts predict a greenhouse will save 50-90 per cent in energy costs compared to an indoor growroom.
So why not greenhouses? Historically, the top reason has been our legal system and the underground nature of the crop. Greenhouses have traditionally been seen as less secure and durable than an opaque metal warehouse. Greenhouses have been seen as more difficult environments to control compared to enclosed growrooms. Standard greenhouses are constructed out of thin, uninsulated materials, making them more prone to temperature fluctuations. With natural light comes natural heat, and in sunny climates like Colorado, greenhouses can potentially overheat.
To control overheating and humidity levels, commercial greenhouses are heavily ventilated. Constantly flushing the greenhouse with outdoor air increases exposure to pests, diseases and pathogens, making it more akin to an outdoor farm than indoor grow room. Another recent risk is airborne hemp pollen. If a greenhouse is in the vicinity of outdoor hemp grows, pollen can enter through vents or fans and pollinate flowering crops. The result is hermaphroditic, or seeded, cannabis that loses much of its value.
Greenhouses also experience variable light levels. A heavily overcast day, for example, typically has only 10 per cent of the light compared to a clear sunny day. If growing year-round, a greenhouse normally requires supplemental lighting and light deprivation systems to achieve the right photoperiod.
Let’s step back for a moment to differentiate between greenhouse strategies. Many cannabis greenhouses are seasonal; they provide added protection for a crop during the normal outdoor season, but close down over winter. Other growers use greenhouses to achieve year-round production for vegetative or flowering crops, or supplement part of a larger year-round operation. In many cases, a grower may use a grow room for cloning and as a veg room, and then move plants to the greenhouse for the flowering stage.
Controlling the photoperiod for flowering crops requires both supplemental lighting and light deprivation systems. Artificial lights extend the short days of the winter, and light dep systems allow for a 12-hour photoperiod during long summer days. Some growers note that adding a light dep system increases the cash outlay for a greenhouse compared to growroom. However, due to the avoided costs of running lights, it is one that is quickly recouped.
Overall, greenhouses have often been seen as a more natural growing method, but one that sacrifices some control over the growing environment.
The Next Wave of Greenhouses: Hybrid Structures
To accommodate for these drawbacks, a new variation of greenhouse has emerged. Part warehouse, part greenhouse, hybrid greenhouses combine insulated walls with standard glazed roofs. From the outside, the greenhouse looks like a warehouse and is nearly as secure. Constructed with metal framing, they are also as durable as a standard commercial building. Most hybrid greenhouses can be rated for any wind load or snow load, making them well-suited for growers in harsh winter climates.
Beyond security and durability, hybrid structures are far more energy efficient than standard greenhouses. An insulated wall typically has an R-value of 10-20. Most glazing materials, in comparison, have an R-value of less than two. Replacing glazing with a durable, insulated structure creates a vastly more energy-efficient structure and more stable temperatures for year-round production.
For these reasons, hybrid greenhouses are emerging as a new niche in the spectrum of growing options–one that is more high-tech and controlled than a standard greenhouse, but still relies on natural light. Some growers are taking this one step further and completely enclosing the indoor environment. Sealed greenhouses are an emerging trend that allows for even greater control over climate conditions.
These structures reduce or eliminate ventilation, so the crops are not constantly exposed to foreign contaminants like molds and pests from outside. Dehumidifiers, heat exchangers, or energy-efficient heating and cooling systems control the climate, providing air circulating and a CO2-rich environment without ventilation.
Adding to this, growers are integrating new lighting technologies to create consistent light levels and a precisely controlled photoperiod. Innovative lighting and control technologies can respond to outdoor conditions, only supplementing as much light as needed. For example, on a cloudy day, a sensor detects the light levels in the greenhouse.
If below peak intensity, controls automatically turn on supplemental lighting, but automated dimmers only turn lights on as much as needed. In this way, greenhouse growers can take advantage of natural sunlight as much as possible while still ensuring consistent peak intensity lighting, eliminating one more disadvantage of the greenhouse grow.
Other technologies involve motors that automatically raise and lower lights to provide intense lighting when they are on, and minimize shading when the lights are off. Finally, automated light deprivations systems seal tightly to the greenhouse frame, creating 100 per cent blackout conditions equivalent to an indoor growroom.
With these advances, high-tech greenhouses now sit squarely in the middle between the indoor and outdoor grow, blending the best of both worlds while eliminating many of the sacrifices of each. As growers continue to demand more controlled, automated, efficient and durable structures, hybrid greenhouses will certainly be here to stay. Moreover, they will evolve along with the industry, carving out a significant niche in the spectrum of structures, and inching growers one step closer to that perfect grow.