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7 Things to Know Before Growing Autoflowering Cannabis

By Grubbycup
Published: April 12, 2022
Key Takeaways

Growing and propagating autoflowering cannabis has some noteworthy differences that gardeners used to growing photoperiod (standard) cannabis need to keep in mind.

Cannabis plants with the autoflowering trait will flower as soon as they are mature enough regardless of the lighting schedule. Unlike regular “short-day” cannabis plants which require a daily long dark period to trigger flowering, autoflowering cannabis plants are “day neutral” and will initiate flowering as soon as they are old enough.

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1. All autoflowering cannabis plants are started from seed.

Non-autoflowering (standard) cannabis plants are either started from seeds or from cuttings (clones). Starting from cuttings is possible because as long as they aren’t exposed to regular continuous long dark periods they will continue to grow without flowering. Cuttings from a plant in vegetative growth will also be in vegetative growth and can be kept under growth lighting until it becomes established as new plants.

Cuttings from an autoflowering cannabis plant, however, are the same age as the plant they were cut from. Since autoflowering cannabis plants flower according to chronological age and not exposure to long dark periods, any cuttings will flower at or near the same time as the donor mother plant. This is why autoflowering cannabis plants must be propagated by seed and not cuttings.

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Out of the many traits carried in C. ruderalis, the autoflowering trait is generally considered the most (if not only) desirable trait.”

2. Genetics plays a large part in an autoflower’s potential harvest.

The autoflowering trait was discovered in a type of short, lanky, quick flowering, low-THC cannabis known as Cannabis ruderalis native to Russia and Eastern Europe. Out of the many traits carried in C. ruderalis, the autoflowering trait is generally considered the most (if not only) desirable trait. Newer varieties of autoflower are a substantial improvement over the original first autoflowers to be intentionally grown outside their native habitat. It is still possible to find seeds from some of the older and rougher plants, which do not produce the quality or quantity that can be expected from other lines that have been improved over the years. Make sure to start with quality auto seeds if a maximum harvest is desired.

3. Feminized autoflower seeds encourage future seed sales.

Feminized seeds produce female plants. It is common practice when growing out non-autoflowering feminized seeds to select the best plants out of those grown to use as mother plants. This allows for taking of cuttings for as many plants as desired, and a mother plant can be kept in growth lighting for as long as desired while her clones are being flowered. This process can be repeated for as long needed, allowing for a single seed purchase to last practically indefinitely.

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When growing feminized autoflower seeds, one might buy seeds, grow the resulting female plants, and then harvest them. Since cuttings can’t be taken and saved, and there are no seeds (because seeds can’t be formed without pollen from male flowers) then new seeds must be purchased for the next round.

Many autoflower growers can save a substantial amount of money by not using feminized seeds and sacrificing a couple plants (male and at least one female; ideally in a separate location) to make their own seeds. Otherwise budget the ongoing costs of buying seeds each time.

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autoflowering cannabis

4. Autoflowering is a simple Mendelian recessive trait.

Without going into too much detail of the science behind it, the autoflowering trait is recessive in cannabis. What this means is that if an autoflowering cannabis plant is crossed with a non-autoflowering cannabis plant, none of the children will show the autoflowering trait. However, if the children are then crossed together, then approximately 25 percent of their children will display the autoflowering trait and will be stable for autoflowering. Any cannabis plant that shows the autoflowering trait can be crossed with any other cannabis plant showing the autoflowering trait and the offspring will all show the autoflowering trait (barring mutation).

5. Autoflowering cannabis plants are time sensitive.

Non-autoflowering cannabis plants have the luxury of being able to extend the growth period for as long as desired before changing the lighting to trigger flowering. If for some reason the plants aren’t at the desired size when planted, the growth period can be extended until they are.

In contrast, autoflowering cannabis plants will flower at a given age, regardless of their size. This means that under poor conditions, even if the plant is only a few inches tall, it will flower anyway once it is old enough, resulting in a disappointing harvest. For autoflowers to produce well, shock and other time delaying events should be avoided if possible. Transplant shock is a common delay, and as such autoflowers should not be transplanted more often than necessary (only once from starter pot to final container is common).


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6. Autoflowers will flower under growth lighting.

Non-autoflowering cannabis plants are kept under lighting without long dark periods to prevent them from flowering. Autoflowering cannabis plants will flower under the same (or any) lighting. This means spare space in a non-autoflowering growth area can be used to flower autoflowering cannabis. This can be particularly useful when designing a continuous harvest type program where the intent is to harvest small amounts often to be more in line with a gardener’s personal usage.

7. Outdoor autoflowers can bring in a midsummer harvest.

In a greenhouse setting, tarps can be pulled to cover non-autoflowering cannabis plants to simulate the long dark periods needed to initiate flowering, allowing for an early harvest.

Autoflowering cannabis plants can be used to a similar effect, without having to cover and uncover the plants. Since they will flower according to age and not conditions, they can be planted in the spring (or later) to generate a harvest in advance of the regular fall harvest. This can come in handy to produce some harvest during the driest part of the year when supplies may be short.

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Written by Grubbycup | Indoor Gardener, Owner & Writer of Grow with Grubbycup

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Grubbycup has been an avid indoor gardener for more than 20 years. His articles were first published in the United Kingdom, and since then his gardening advice has been published in French, Spanish, Italian, Polish, Czechoslovakian and German. Follow his gardening adventures at his website grubbycup.com.

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