Outdoor & Greenhouse Growing
Cannabis has traditionally grown outdoors, where regional cultivars became stabilized to thrive in their local climates. Light from the sun, natural ventilation, and minimal need for equipment certainly make outdoor cultivation the most affordable way to cultivate cannabis. Cannabis plants grown outdoors may also grow larger, heartier and may produce a larger overall yield when cared for carefully. Growing outdoors, however, does carry the added risk of pests, cross-pollination, contaminants, and harsh weather, commonly resulting in a lower quality end-product compared to indoor grows, where conditions are more able to be fine-tuned.
Greenhouses are, for many, the best of both worlds, allowing cultivators better control over their plants' environment, while still taking advantage of the sun's rays. The added protection from weather and the heat-capture of a greenhouse also allow growers to expand their growing season, which can be key in areas like ours where early, rainy Falls frequently break outdoor cultivators’ hearts. In a greenhouse, light can be supplemented or blocked out to control when flowering begins, meaning multiple crops can be harvested each season. They may even be completely enclosed and supplied with filtered air to help prevent pests and contaminants from reaching the plants.
Benefits to Growing Outdoors
Cultivating cannabis outdoors has many benefits. The sun provides free energy with high output across the spectrum, as well as a healthy amount of UV light. Plants have evidently evolved to make use of the sun's light and it provides the best quality light available.
The electricity savings alone dramatically reduce the cost of growing outdoors compared to running artificial lights indoors. Each 1000w bulb can consume a whole kilowatt hour (kWh) each hour, which costs $0.10-$0.20 depending on electricity rates. During an 18/6 veg cycle, each bulb could cost $2-4 to run each day, which definitely adds up over a 11-20 week growing period. Growing with sunlight can save thousands of dollars in electricity each month, even for as few as 100 plants. The environmental cost of cultivation is of course also offset by relying on natural light.
Growing outdoors can also increase yield. The sunlight, breeze and natural vegetative and flower cycle causes the plants to grow very large. Because the flowers need to enter flowering naturally when the days grow shorter in August, the period the plants spend in vegetative growth often stretches from as early as April to August. When flowering begins, a single outdoor plant could have hundreds of nodes for buds to develop. The buds themselves may be smaller and lower quality than those grown indoors, but the yield can be much higher.
Considerations For Growing Outdoors
When planning for outdoor cannabis cultivation, growers need to take into account all the elements of the environment that they can’t control. The amount of sunlight and when plants move into flower, the weather, and the amount of sunlight may be outside of a grower's control, but they can make decisions to mitigate their risks. Growers can plan out their growing season to align with their local climate, day length, and by carefully selecting their strains based on desirable attributes for growing in their region.
Growing season : Outdoor cannabis plants normally begin to flower around August and, depending on the strain, will flower anywhere between 8-16 weeks for a harvest in late September or October. Because most of the plants will move into flower at the same, the entire field may need to be harvested over several days once the plants have matured.A big consideration for outdoor growers is when frost will begin to set in. Early frost will kill cannabis plants before they can be harvested so the final harvest date is a balancing act between the maturity of the flower and the overnight temperature.
Strain selection: It’s best to select hearty strains that are resilient to outdoor stresses and are well suited for your climate. Indicas may be better suited for cooler climates with shorter growing seasons, but sativas can still perform great, especially when grown in a greenhouse. Some plants also have better protection against certain pests, so if you are cultivating in a region with specific pest concerns such as thrips or aphids, some strains may be naturally defended. Because of the lower quality of outdoor flower, most is converted to hash and concentrates, so selecting strains with genetically high cannabinoid content and dense trichome production may be a good deciding factor.
Outdoor irrigation: Outdoor irrigation works much the same way that indoor irrigation does. Pumps deliver nutrient rich water through long hoses direct to the plants in the field. Because of weather and seasonal changes, watering of outdoor plants is usually a more manual process. Rain can saturate the soil and remove the need for further watering, but nutrients may still need to be supplemented by foliar spray or light irrigation.
Limitations of Outdoor Cultivation
Unpredictable weather or changes in temperature can slow or stop plant growth and dips below freezing can kill entire crops. There’s no barrier to pests, pollen and airborne fibers and adulterants, so the quality of the flower will likely be lower. Little to no control over the natural flowering process means there will be one large harvest instead of rotating crops. Cannabis also bioaccumulates elements found in the soil so natural soils should be clean of heavy metals and will need to be refreshed and tilled to reintroduce nutrients to the soil.
Weather : Some regions have more predictable climates than others. Warmer areas on the west coast of Canada have a longer, more temperate growing season, while northern climates are faster to get snow and ice. Excessive rain and humidity can cause powdery mold issues, root rot, and increase the prevalence of pests. Cold weather can freeze plants and if ice crystals develop within the delicate vascular tissue in the stems and roots, they could die. Climate change is contributing to more extreme weather events and extremes in temperature each year. Poor weather can have a serious and lasting impact on cannabis plants.
Pests: Because there is no physical barrier to prevent insects from reaching outdoor cannabis, without proper prevention, infestations are inevitable. Outdoor growers often have to use approved pesticides to control any pest populations. Biopesticides, or “good bugs” are a great tool to control pests, but some can leave the area and have to be introduced several times over the season.
Pollination: A single male plant produces millions of grains of pollen, each capable of producing a seed. If male plants aren't separated early, entire crops and neighbouring farms could be pollinated. If the flower becomes pollinated, it will divert energy from trichome production to produce the seeds, causing lower cannabinoid content.
Fibers and Adulterants: Dirt, soil, pollen, hair, and lots of other natural fibers float through the air and stick to the sticky trichomes that cover the buds and leaves. Some growers may choose to wash their outdoor flower after harvest or process the flower for concentrates, where the adulterants can be removed as part of the extraction method.
Bioaccumulation: Cannabis is a bioaccumulator and will internally concentrate elements found in the soil where it grows. Natural soils likely developed their nutrients from dissolving minerals and a layer of decomposing organic matter that sits on top of the soil. Cannabis will strip many of these nutrients from the soil and store them in its roots and plant structures. Cannabis is actually being used in some parts of the world to remediate harmful heavy metals and radiation because of its strong bioaccumulation properties. If these harmful chemicals and elements already exist in your starting soil, they can adulterate the flower and trim of the cannabis plants.
Greenhouse Cultivation
Greenhouses are the middle ground between growing indoors and outdoors. Growing in a greenhouse allows growers some of the control of growing indoors, alongside free energy from the sun. They are often used in combination with outdoor cultivation to allow for multiple harvests or to nurture young plants until they are strong enough to weather the outdoors.
Benefits to Growing in a Greenhouse
Many licensed producers in Canada use greenhouses for their cultivation because of the added control and other benefits growing indoors offers. Greenhouse growers can supplement the light of the sun with artificial lights so plants still receive ample light on rainy or cloudy days. They can integrate heating and active and passive cooling systems to keep the temperature in an ideal range. Because greenhouses trap the heat from the sun, they also allow growers to plant earlier and harvest later, lengthening their growing season.
Without the additional light before sunrise and after sunset, the plants would naturally move into flowering. Growers may try to get multiple harvests in a season by blacking out light to push their first crop into flower early by the end of April or May, harvesting in June or July, then running another batch of plants between July and November, supplementing light to extend the season for this second harvest.
Greenhouse ventilation depends on what and where you are growing. In really warm climates, having open sides and active cooling and ventilation are needed to prevent it from getting too hot. Colder climates may maintain a positive pressure greenhouse with closed walls and filtered fresh air vented in to cool the room. This can help keep out unwanted pests and keep the temperature from dipping at night.
Cannabis can be grown outdoors at a lower cost than what's possible in an indoor facility, but the flower is typically lower quality (though many talented outdoor growers have proven this general rule wrong and would strongly dispute this generalization). Free light from the sun, natural ventilation, and minimal construction make outdoor cultivation the cheapest and most environmentally-friendly way to cultivate cannabis. Cannabis plants grown outdoors will also grow larger and have a higher yield. Growing outdoors, however, introduces additional risk of pests, pollination, contaminants and weather. The end product is often a much lower quality than flower grown indoors because of these environmental factors.
Greenhouses allow growers better control over their plants' environment, while still taking advantage of the sun's rays. Greenhouses are naturally warmer than the outside air and the added protection from weather and heat capture allow growers to expand their growing season. Light can be supplemented by artificial lighting and blocked out by blackout shades to control when flowering begins so multiple crops can be harvested each season. Greenhouses may be completely enclosed and supplied with filtered air to help prevent pests and contaminants from reaching the plants. Open greenhouses can benefit from increased natural ventilation, but they are at increased risk of contaminants.
Each grower will weigh the same pros and cons, but arrive at their own decision based on their own priorities, which typically include some combination of cost, smokability of the end product, trichome and cannabinoid production, risk tolerance, and environmental sustainability. Why do you choose to grow where you do?
References:
Guroodita, Monica. "Outdoor Cultivation". Cannabis Cultivation and Processing, 11/03/2024, Centennial College, (https://e.centennialcollege.ca/d2l/le/content/1078529/viewContent/13757823/View). 15/01/2024