Growing Autoflowering Cannabis

A Complete Guide to Auto-flowering Cannabis

Cannabis horticulturists have been perfecting how to grow marijuana for decades. They have discovered the perfect nutrient ratios for optimal growth, mastered the mimicry of outdoor growing conditions indoors, and pinpointed the exact amount of light to utilize during each stage of growth. However, growing a cannabis plant can still be tricky, and some of the equipment needed can be costly.

One of the most critical components of growing a photoperiod cannabis plant is providing the right number of light hours to support vegetative growth and knowing when to reduce the light hours to support flowering. Getting this wrong can be devastating to a grower’s goals because plants with inadequate or excessive light may become stressed, resulting in low yields, potentially hermaphroditic traits, self-pollination, or the pollination of an entire crop of flowering (female) plants.

To reduce the complications of growing photoperiod plants, growers and breeders have cultivated a strain of cannabis plant that is crossed with Cannabis ruderalis called auto-flowering cannabis. Growers with less experience, limited space to grow, or a small start-up budget often prefer auto-flowering cannabis for its short stature and short life cycle.

What is Auto-flowering Cannabis?

Photoperiod cannabis plants enter the flowering stage when the light cycle is switched to 12 hours of light and 12 hours of darkness. Alternatively, auto-flowering cannabis blooms without the need for an external trigger, such as light schedule changes, because the plant switches into flowering on its own.  In other words, auto-flowering cannabis plants begin flowering as soon as they reach a certain age, independent of regimented “flower phase” hours of light exposure, which releases growers from their timers and light schedule responsibilities.

Many varieties of auto-flowering cannabis take only ten weeks to reach the harvesting stage from seed. However, there are some varieties called “super autos” that take more than 100 days to reach the harvest stage and may reach over 6 feet tall.

How They Are Made

The most well-known varieties of cannabis are Indica and Sativa. However, a little-known strain called Cannabis ruderalis is responsible for the development of auto-flowering strains.

Native to Southern Siberia, this strain of cannabis has adapted to withstand harsh environments, cold temperatures, and minimal amounts of light. Ruderalis plants are short and stalky, growing just 2 – 3 feet from the ground.

Auto-flowering cannabis plants are a cross of the photoperiodic Indica or Sativa strains and the Cannabis ruderalis strain. The resulting strain is either a Sativa-dominant or Indica-dominant auto-flowering strain.

The Pros and Cons of Auto-flowering Cannabis

Short-statured, fast growing, low-THC auto-flowering cannabis plants gained popularity in the 1990s, although some growers still opt for classic, photoperiodic plants. Below is a summary of the pros and cons of auto-flowering cannabis.


Short Growing Time and Quick Harvest

As mentioned above, most strains of auto-flowering cannabis take only ten weeks to reach the harvest stage. Some strains like Grapefruit begin flowering around two weeks and are ready to harvest in as little as eight weeks. The short growing time is a considerable advantage to gardeners who want to keep things speedy and discreet.

Compact Size

Auto-flowering cannabis plants are typically much smaller than other strains. The hallmark of Sativa strains is how tall they grow, with some of them capable of reaching over 15-feet-high. Photoperiod Indica-dominant strains are typically short and bushy with broad fanleaves and thick branches. When crossed with the Ruderalis strain, the result is a much smaller, but still an Indica-dominant auto-flowering cannabis plant with a much shorter (~10-week) life cycle.

Stealthy growers or those with limited space often choose to grow discreet, low-profile auto-flowering cannabis plants to optimize the capacity of their grow area.

No Lighting Changes Needed

In order to flower, auto-flowering cannabis plants do not require changes to their light cycle. Many growers continue to give their auto-flower plants 16 – 18 hours of light per day during the entire cycle of growth.

Photoperiodic cannabis plants are incredibly sensitive to light changes. They require 12 hours of light and 12 hours of dark during the flowering stage and rarely grow any larger once that stage has begun. Additionally, these strains can be stunted or shocked by light leaks, which are relatively common for indoor growers.

Multiple Harvests per Season

When growing outdoors, the short growth cycles of auto-flowering cannabis plants (~10 weeks) allows for 2 – 3 harvests per season whereas outdoor photoperiod plants are harvested once each season, with some Sativa-dominant plants taking 8 months to fully mature.

High Tolerance of Temperature Changes

One of the hallmarks of auto-flowering cannabis plants is their ability to tolerate fluctuations in temperature. Where photoperiod cannabis plants often experience shock if exposed to sudden bursts of cold weather, their auto-flowering cousins are resilient. The hardy nature of auto-flowering cannabis plants is often what attracts growers who plan to grow their plants outdoors, as unpredictable weather has been known to destroy or damage entire crops of cannabis.


Potentially Higher Electricity Costs

While there have been substantial advancements in grow light technology, the fact remains that they draw much more power than the average household lightbulb. Most growers know that their electricity bill will go up significantly once they start using grow lights. However, the costs generally decrease when photoperiodic plants are switched to a 12/12 light/dark schedule.

As mentioned above, many growers provide their auto-flowering plants with 16 – 18 hours of light and 6 – 8 hours of darkness per 24-hour-period for the entire cycle of growth, resulting in electricity costs that are not reduced during the flowering phase. Additionally, with auto-flowering plants that are grown year-round, the electricity bill is much higher than it is with photoperiod strains.

Smaller Yields

Fast harvests and small plants are an excellent benefit to growers that value speed and stealth. However, those who want big yields from their plants may be disappointed by the yield most auto-flowering plants provide, which is between 10 and 50 grams per plant. The average Sativa plant takes 26 weeks to fully mature but makes up for the length of time by yielding up to 45 times more marijuana than the average auto-flowering plant. However, consider that much of this difference can be made up by the number of auto-flower plants and harvests the grower can cycle through each season.

Lower Potency

Cannabis Ruderalis is low-THC and, therefore, does not have much of a psychoactive effect when consumed by humans. Thus, when Ruderalis genes are mixed with Sativa or Indica genes, the result is a less potent strain of marijuana. Some growers who prefer to cultivate marijuana primarily high in CBD may find auto-flowering strains suit their desires. However, those after the highest THC content may be disappointed by the potency of many auto-flowering strains.

It is worth noting that auto-flowering strains can produce marijuana with a high THC content. For example, Auto Gorilla Glue #4 has between 24% and 30% THC, which rivals some of the most potent Indica and Sativa photoperiod strains.

Growing Cannabis is More Accessible Than Ever

Humans have been cultivating marijuana for centuries. In recent years, scientific research has allowed growers to eliminate the most persistent problems in cannabis horticulture. They have been able to tailor their growing methods to a variety of space, budget, time, and experience constraints. One of the most significant advancements in growing marijuana in recent years has been the development of auto-flowering cannabis strains.

Auto-flowering cannabis has allowed growers of all skill levels to cultivate a robust marijuana plant successfully. It has eliminated the need for temperamental lighting systems and has widened the margin for error in a growing environment. Those with limited space can now enjoy the process of growing their own cannabis, as their small size makes them easy to fit into even the tiniest closets. The quick grow times allow for multiple harvests during an outdoor growing season, which can also bridge the gap between the regular cannabis and auto-flower cannabis yields.

Online cannabis seed banks like i49 provide a catalogue of auto-flowering varieties to fit any grower’s goals—check out the seed selection today!

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