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Why should cultivators select different genetics for outdoor farms than they would for indoor grow sites or even greenhouses? Essentially, because outdoor growers have less control, more space and lots of free light. Although outdoor farmers are at the mercy of Mother Nature when it comes to weather, they do enjoy some advantages that indoor growers and greenhouse cultivators cannot take advantage of in the same cost-effective manner.

This article examines outdoor cannabis varieties that are grown for flower, not industrial hemp that is grown for fiber or seed production. It also will differentiate between varieties for summer cultivation and year-round outdoor cultivation. What’s the difference? Outdoor is outdoor, yes? Not exactly.

In places like Canada and the Northeastern U.S., the summer growing season can be as short as three months, because temperature-sensitive crops like cannabis must be planted after the last frost of the season, which is typically May, and harvested before the first frost of the season, which is typically September. In the Southern U.S., while the growing season is more than twice as long, it still eventually comes to an end.

In contrast, tropical or equatorial regions allow cultivation businesses to plant outdoors year-round. In places like Colombia, Central Africa and Thailand, growing is non-stop as warm temperatures and sunlight are present the entire year. Outdoor growers in these climates may consider selecting varieties with different characteristics than they would for production during the limited summer months in northern regions.

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Desirable Characteristics for Summer Crops

Early flower onset: Early flowering crops are critically important for regions with short growing seasons. Frost is a concern, as well as rainy weather that often accompanies the arrival of fall. Rainy and cold conditions, even just for a few days, can rapidly decimate a cannabis crop that is nearing harvest. Mold can proliferate through a damp crop, while freezing can cause plant cells to die.

Early onset means that plants easily and rapidly initiate flowering. These varieties often display a profusion of female flowers while still in the vegetative stage. Pre-flowers are common with most cannabis varieties, and they naturally begin to emerge between the main stalk and lateral branches of the plant after about six or eight weeks of vegetative growth. This is normal and can help growers identify female plants early. In early flowering varieties, this goes beyond just a few pre-flower pistils. Although the plant is still in vegetative growth, it continues to produce more and more female flowers. Plants that display this characteristic rapidly begin flowering once introduced to uninterrupted long nights, and they typically have a short flowering cycle. These varieties that complete the crop cycle quickly can help growers negotiate a short outdoor growing season.

Resistance to botrytis: While total resistance to botrytis is unlikely, growers can seed varieties that are less susceptible to botrytis infection. Botrytis, or gray mold, is a fungus that thrives in cool and wet environments. The end of the summer growing season can present a challenge to cultivators that have no control over these potentially devastating conditions. According to the University of Massachusetts Greenhouse Crops and Floriculture Extension, “[spore] germination and infection depends on a film of moisture for eight to 12 hours, relative humidity of 85% or greater, and temperatures 55 to 65°F.” These types of prolonged conditions can easily wipe out the previous months of hard work.

One way to minimize outdoor losses from botrytis is by cultivating varieties with a low bract-to-leaf ratio. This refers to the density of the cannabis flower, which is a cluster of bracts, pistils and leaflets. If the flower has a high bract-to-leaf ratio (more bracts and pistils than leaflets), it will be a very dense bud once it is dried. Although solid, heavy buds are usually more desirable for dispensary retail sales, in the field they are much more susceptible to disease infection as moisture can become trapped in the flowers. However, a low bract-to-leaf ratio means the flower tends to be more airy, open and leafy. This lack of density can allow for more air flow, potentially minimizing the occurrence and severity of botrytis infection. Airy buds typically yield less biomass, but most farmers would prefer a lighter yield over a completely ruined crop, as revenue loss from lower yields can be offset by lower production costs. A low bract-to-leaf ratio is more common with sativa-dominant or equatorial cannabis varieties.

Automatic flowering: Like the early flowering varieties, autoflowering varieties are especially useful for growers that experience short summers. Unlike most cannabis varieties that begin to flower when they experience long periods of uninterrupted darkness, autoflowers initiate their reproductive phase as a function of maturity. A few weeks after seeding, most autoflowering varieties begin to show pistils and start the flowering process. This is due to the influence of their ruderalis genetics, which is a “weedier” type of cannabis that flowers in the wild regardless of daylength. In regions with longer summers, autoflowering varieties can allow the grower to harvest more than one crop per outdoor season, meaning they can realize double the revenue from the same plot of land.

One feature to be mindful of is most autoflowering varieties are notoriously short. This is directly related to the short vegetative growth period that the grower cannot extend. To compensate for their short stature, cultivators may choose to plant at a much higher density to improve crop yield. In an outdoor bed, one autoflowering plant per square foot is recommended, which is one-third or one-fourth the amount of space allotted for larger varieties.

Desirable Characteristics For Year-Round Outdoor Cultivation

Ryan Douglas next to a sativa-dominant cannabis plant. Sativas can grow to heights in excess of 6 feet.
Photo courtesy Ryan Douglas

Large size: Large plants are an appropriate selection for year-round outdoor cultivation. Outdoor growers are not restricted by ceiling height, so there is no pruning or training to force the plant to grow in a certain direction or fill out a predetermined space, such as a 4-foot-wide grow bench. Instead, outdoor growers can allow vigorous plants to grow large, and reap the accompanying massive harvest as a result. Large plants and strong sunlight are the perfect recipe for huge yields, and because commercial outdoor growers are mostly concerned with biomass production, the larger the plant, the more biomass there is to be harvested.

Equatorial varieties are appropriate for equatorial regions, so sativa-dominant plants that grow large also are appropriate for year-round outdoor production. Don’t worry if these varieties require a slightly longer flowering period to finish because the growing season never ends. An 80/20 sativa-indica mix should help tame the long flower period that is common with sativa-dominant varieties. For big plants, plan on allotting at least 10 square feet per plant, and anticipate heights in excess of 6 feet.

Reduced sensitivity to photoperiodism: Most year-round growing regions are near the equator, where there are 12 hours of light and 12 hours of darkness for every 24-hour period. Depending on the tilt of the Earth as it circles the sun, days may be shorter or longer by up to 30 minutes during some months, but it is generally a 12/12 light cycle year-round. These conditions can present a problem for growers that seed directly into the ground or transplant rooted clones outdoors. Seedlings can begin flowering shortly after emerging from the ground, and rooted clones can begin flowering shortly after being transplanted. This can result in extremely short plants and an accompanying small yield. To battle this problem, outdoor growers need to break up long nights with interruption lighting, which can provide a logistical problem because most outdoor crops are several acres in size.

By growing native equatorial varieties, cultivators may avoid the need to provide interruption lighting. Equatorial varieties appear much less sensitive to photoperiodism, meaning they will not initiate flowering as rapidly as an indica-dominant plant when exposed to long nights. This is because their survival depends on it. In nature, if a seedling begins to flower once it emerges, it will never compete with the lush vegetation surrounding it. Where there is no winter to kill off vegetation, competition for sunlight is fierce, and cannabis plants must remain in a vegetative growth state for several months—even under 12/12 light conditions—in order to penetrate the plant canopy and unfold into the sunlight. For survival, it’s not in the plant’s best interest to begin flowering as soon as it senses prolonged darkness.

Outdoor growers near the equator should take advantage of this feature. By planting sativa-dominant varieties, a cultivator can skip the need for interruption lighting. Plants will grow vegetatively in the field and not initiate flowering for several months, even during long nights. This feature allows the crop to size up to an appropriate height before it begins to produce flowers.

Bracts are the parts of the cannabis flower from which pistils emerge. A higher bract-to-leaf ratio means a denser bud.
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Heavy yielding: Sun-fed plants that receive adequate water and proper nutrition can be a powerhouse for flower production. When selecting varieties for year-round, open-field cultivation, growers should seek heavy-yielding varieties. The higher yielding the plant, the more profitable the cultivation project. Aim for varieties that yield between 500 and 800 grams per plant during a six-month life cycle.

Yield should also be considered in terms of extraction efficiency because many outdoor crops are destined for cannabinoid extraction. Cannabinoids are compounds produced within the resin glands that cover the plant, and some cannabis varieties produce more oil than others. Selecting a variety that produces more oil will result in more profit per acre of production. Outdoor growers should select varieties with a minimum 10:1 extraction ratio, where 10 kilograms of dry flower will yield 1 kilogram of oil.

This series has shown how different cannabis varieties can be utilized to improve the operational efficiency of a cultivation business. Whether cultivating indoors, outdoors, or in a greenhouse, growing for genetic fit can help commercial operations avoid unnecessary expenses and grow healthier crops. The next time you add new genetics to your cultivation program, keep these tips in mind, and you’ll find yourself spending less time working on the crop and more time reaping the rewards.

Ryan Douglas is the owner of Ryan Douglas Cultivation, LLC. He has worked in commercial horticulture for 20 years and specializes in legal cannabis start-ups.