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Autoflowering seeds

Autoflowering strains have been experiencing a golden age in the last few years. These automatic flowering strains have been involved in a surprising and fast evolution that turned them into the most popular genetics of the moment for both growers and breeders. A growing number of cannabis growers prefer the fast, discreet and delicious autoflowering strains.

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Autoflowering seeds

Sweet Mimosa XL Auto®

Autoflowering seeds

Tropicanna Poison XL Auto®

Autoflowering seeds

Purple Punch OG XL Auto®

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Autoflowering seeds

Skywalker OG Runtz XL Auto®

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Autoflowering seeds

Strawberry Banana Gelato XL Auto®

Autoflowering seeds

Sweet Zenzation XL Auto®

Autoflowering seeds

+Speed Auto®

Autoflowering seeds

Big Devil #2 Auto®

Autoflowering seeds

Big Devil Auto®

Autoflowering seeds

Big Devil XL Auto®

Autoflowering seeds

Black Cream Auto®

Autoflowering seeds

Black Jack Auto®

Autoflowering seeds

Bloody Skunk Auto®

Autoflowering seeds

Bruce Banner Auto®

Autoflowering seeds

Cream Caramel Auto®

Autoflowering seeds

Cream Mandarine Auto®

Autoflowering seeds

Cream Mandarine XL Auto®

Autoflowering seeds

Crystal Candy Auto®

Autoflowering seeds

Crystal Candy XL Auto®

Autoflowering seeds

Dark Devil Auto®

Autoflowering seeds

Devil Cream Auto®

Autoflowering seeds

Fast Bud #2 Auto®

Autoflowering seeds

Fast Bud Auto®

Autoflowering seeds

Gorilla Girl XL Auto®

Autoflowering seeds

Green Poison Auto®


What are autoflowering strains?

Autoflowering seeds (also known as “automatic seeds” or “auto seeds”) produce cannabis plants that flower regardless of the hours of light that they receive (photoperiod).

The large majority of cannabis strains are photoperiod dependent and, in these strains, flowering starts when the shorter days and longer nights arrive: the beginning of flowering is determined and regulated by the photoperiod. And as cannabis growers know, the photoperiod also regulates the vegetative phase in which the plants can be indefinitely maintained with artificial lights, creating long days and short nights.

On the other hand, autoflowering strains start flowering according to their age. The autoflowering strains that we offer at Sweet Seeds® start flowering when they reach to around 3 weeks, counting from the appearance of the cotyledons, which usually happens when the plants develop their third or fourth pair of real leaves. For this reason they can be grown and flower in any time of the year, as their flowering is not dependent on the photoperiod or the season of the year when they are grown.

This group of modern autoflowering marihuana strains represent the fastest flowering strains known today, being able to complete their flowering stage in only 5 weeks from the beginning of flowering. Considering these 5 weeks of flowering together with the 3 weeks of the vegetative phase, we would harvest them about two months after the germination of the seed.

Tall-stemmed autoflowering strains

At Sweet Seeds® we work to develop easy-to-grow plants, very aromatic and tasty, but they also feature a vigorous structure with a taller size when compared to the original autoflowering genetics and, above all, featuring higher yields and stability.

Autoflowering strains usually don’t grow taller than one meter of height. This happens because most of the breeding improvement projects on autoflowering strains have been performed by using autoflowering strains and commercial indica strains featuring fast flowering. This small size feature was a bit scarce for the needs and expectations of some cannabis growers who demand taller-stemmed autoflowering plants. Considering this request, Sweet Seeds® focused in the creation of tall-stemmed autoflowering strains, giving birth to the Big Devil® family and our “XL” autoflowering strains, developed to satisfy the clients who demanded tall-stemmed autos. When grown with optimal conditions these strains easily exceed the meter of height, helping them to accomplish an important increase in production, making them the most productive autoflowering seeds.

This tall-stemmed trait was achieved by introducing new genes with sativa predominance in the genetic pool of the autoflowering strains.

Purple-flowered autoflowering strains, The Red Family

In the year of 2013 we presented the new, exotic and attractive purple-flowering autoflowering strains that we baptized as “The Red Family”. The most appealing characteristic of these varieties is how beauty they get when the buds achieve maturity, showing a dark purple color.

Strains from The Red Family are the result of the hybridization and subsequent stabilization between Sweet Seeds® genetics and a curious exotic purple-flowered autoflowering strain. The purple-flowered characteristics are inherited from an autoflowering genetic with ancestors from the Chitral region in the Pakistani Hindu Kush, very close to Afghanistan.

Around 90% of the specimens from The Red Family acquire purple or reddish tones in the flowers and some specimens also acquire purple tones in the leaves while flowering. After harvested and dried, the buds gain a very dark purple tone, almost black.

Outdoor autoflowering strains

Although the autoflowering trait of most of the modern autoflowering varieties are inherited from lineages of cannabis rudelaris, coming from zones with a cold climate, this does not mean that these new and improved autoflowering strains can handle with and correctly develop during the European winter.

In the winter, with few hours of light and if the temperatures drop to below 10ºC by night, these strains slow down their development and the flower production. They could even stop growing under these conditions. When temperatures drop to around 0ºC, the meristems and the leaves are damaged and our small autoflowering plants could die.

The best season of the year to have them showing their maximum potential is from spring to autumn, when the temperatures are milder. The more hours of light they get, the better the final results will be.

Another important information regarding the ideal growth parameters for these plants is the size of the pots that should be used for these short and fast strains. These plants don’t develop big root systems, for which they don’t need very big containers in the beginning. The ideal is to plant them in a small pot (of 1 litre, for example) right after they are germinated between paper towels (or with your favourite method). This way we make sure that the soil does not remain excessively moist for a long time, because excess of humidity and lack of oxygen in the soil along the first weeks of development could inhibit root growth, be a focus of deficiencies and even fungous infections in the root system and in the base of the main stem. Considering that autoflowering strains should develop fast, any problem or stress that could affect them within the first weeks will negatively affect its final height and production.

When the small plants reach to around their 17th day of life, we can transplant them to their final pots of 5-10 and until 20 litres. The transplants should always be carefully performed, without braking or damaging the roots and the new soil must be identical to the first one used. In this moment we can take the opportunity to infect the soil with beneficial fungus or bacteria, (Mycorrhiza, Trichoderma, etc ...) and we can also cover the stem of the plants that may have stretched excessively, because when buried under soil these stems end up producing new roots. At this point the flowering stage starts.

Tall-stemmed autoflowering plants, such as strains from the Big Devil® family, can be transplanted at the beginning of flowering to a 10 litre pot or bigger.

Using a good soil, there is no need to feed the plants with liquid fertilizers for the first 15 to 20 days of life of the plants. But using a root stimulator in the first waterings will help in the fast development of a strong and healthy root system. From this point we can start using nutrients and stimulators as we would do with any other marihuana plant. A good flush at around the 5th or 6th week of life will help to keep low levels of salts in the soil. With tall-stemmed autoflowering strains like Big Devil® or the “XL” genetics we can use the grow fertilizer during the first week of flowering, so that the plant gets enough Nitrogen to fulfill the needs of the vigorous growth trough which they undergo during the first weeks of flowering. A lot of plants threefold their size.


  • Avoiding mold: a lot of outdoor growers from humid zones where cannabis plants are very susceptible to fungus attacks due to environmental conditions, started growing these strains also in the spring to avoid the climate conditions of September-October and, with this, keep the plants away from the fungus attacks that end up rotting the bigger buds. There are also lots of growers from zones in the high mountains and cold zones who are choosing to grow these strains in the spring-summer season, obtaining very good results.
  • Fast development and flowering: the autoflowering strains conclude their vital cycle very fast, making it possible to harvest aromatic and resinous buds two months after the germination of the seeds.
  • Discretion: their fast development and their moderate stature turn them into very fast and discreet plants. This is especially important for cannabis users who live in places where laws are nonpermissive or intolerant with marihuana growing for personal use.
  • Avoiding thieves: for being discreet and out of season, these plants are harder to detect by thieves or undesirable eyes.
  • Absence of light contamination: flowering independently of the photoperiod allows plants to flower even when exposed to light contamination as the one produced by street lights that inhibits flowering in photoperiod-dependent strains. This advantage, together with their short stature, turns them into ideal plants for urban growing in balconies, small gardens, etc.

Indoor autoflowering strains

When grown indoors with artificial light, the best results can be obtained with photoperiods of 18 hours and up. Many cannabis growers grow these plants indoor with 20 hours of light and 4 hours of darkness during all the life cycle of the plants, achieving excellent results.

The size of the pots and the use of liquid fertilizers is identical to the one described in the previous chapter of outdoor growing.


  • Fast development and flowering: in indoor growing they are selected for the quickness of their vital cycle, being ready 60-70 days after the germination of the seed.
  • Saving energy and effort: although autoflowering strains must be grown indoors with a photoperiod of 18-20h of light and 4-6h of darkness during the whole life cycle of the plant, this excess of light, compared to the 12h for flowering of photoperiod-dependent plants, is more than compensated by the month of growing duration economized when growing autos. The result is a relevant saving of energy expenses and a saving of one month of growing work, consequently saving also on fertilizers.
  • Benefiting from empty holes from the mother and cloning areas: growers and collectors of clones who have a grow area dedicated to mothers and cuttings, can also use the empty spaces from this area with a 18/6h photoperiod to flower autoflowering plants.
  • High quality autoflowering varieties: modern autoflowering varieties don’t loose to photoperiod-dependent polyhybrids, whether it is in vigor, resin production, cannabinoid levels, type and levels of terpenes or flower density.

A bit of history. Origin of the autoflowering strains

To look into the origin of most of the autoflowering genetics we have to take in consideration a lot of cold zones from Eastern Europe (Hungary, Southern Siberia, Russia...) and Central Asia, where the first and wild Cannabis Ruderalis genetics originated. In these regions the climate conditions (especially the cold temperatures and long winter) only allow for three or four months per year of adequate conditions for their development and reproduction. One possibility was that these types of strains could have developed this especial autoflowering characteristic because it represented an adaptive improvement that allowed them to flower and produce seeds in the short period of adequate climate, thus perpetuating its own species in these inhospitable places.

Cannabis Ruderalis is a subspecies of Cannabis Sativa. The subspecies Cannabis Ruderalis was first described and scientifically catalogued by the Soviet botanics Dmitri Janischewsky in 1924 and was considered by then as bad weed, not much appreciated for medicinal and recreational uses for its low content of THC and low quality of its organoleptic characteristics (taste and aroma), while it was disregarded as raw material for industrial use (fiber and paper) due to the small size of the plants.

It is also possible to find wild autoflowering plants similar to Ruderalis in some zones where cannabis growing was common in the past. The most important of these zones is the central zone of North America and Canada, although it is possible to occasionally find disperse populations all over the country. These populations have been growing wild for years and without man selection they lost many of the selected traits, adapting to the environment.

Maybe the autoflowering genes can be found in the gene pool of most cannabis strains. And Ruderalis strains, along with other wild autoflowering strains, might have arose from a process of natural selection of short flowering in populations of Cannabis Indica. Nowadays, the general consensus is that all “domesticated” cannabis strains and all the wild strains proceed from the same source of genes, making it very plausible that many cannabis strains preserve autoflowering genes in their gene pool.

After observing the type of inheritance that expresses the autoflowering trait, at Sweet Seeds® we tend to believe that perhaps the autoflowering genes are “damaged” genes which can not carry out their mission of flowering according to the photoperiod, when the hours of light decrease.

After the 70’s some pioneers at cannabis breeding observed the potential concealed by these autoflowering strains and started to cross them with high-THC marihuana strains, with the final goal of taking advantage of these autoflowering genetics which provided fast flowering, short stature, acclimation to cold zones and resistance to local insects and diseases. This is how the first improvement programmes to introduce these characteristics in strains with high THC content and pleasant aroma started.

The first documented experiments with crosses between several Ruderalis strains and high-THC strains were performed by Ernest Small from Agriculture Canada in Ontario in the course of the 70’s.

During the 80’s the famous cannabis breeder Neville, owner of the legendary and pioneer Seed Bank experimented with crosses between Ruderalis and some strains as for example Mexican strains, Skunk #1 and several Indicas. Although some of these Neville’s crosses matured much earlier than the classic Mexican strains, they featured lower THC content and were very unstable regarding flowering time and calyx-to-leaf ratio in the buds.

Also during these years, in British Columbia’s gulf islands (Canada), an anonymous outdoor cannabis grower observed that in the photoperiod-dependent cannabis strain that he was growing for some years, harvested in October, every year a few specimens matured much earlier, by late July or beginning of August. After several years of selection he obtained a seed line that kept the autoflowering trait and preserved the effects and aromas of his beloved strain of seeds. This is how Mighty Mite was born.

Mighty Mite was quickly converted into a very popular plant, providing the Canadian growers with harvests before summer and before the arrival of mold. Also in Northern zones it substituted many fast Indicas acclimatized to cold areas. Lately this strain was also cultivated by indoor growers and was hybridized with more potent strains.

One of the first autoflowering strains presented by Sweet Seeds® in the beginning of 2009, Speed Devil Auto®, was developed from a selection of specimens from a Canadian autoflowering seed line received in a seed interchange and was submitted to several generations of selection. We believe that it is very likely linked to the famous and primitive Mighty Mite.

Sweet Seeds® in the development of modern autoflowering genetics

Above anything else we, the Sweet Seeds® breeders, consider ourselves users and collectors of genetics. It is to say that we search and select the best strains that we find, to preserve them indefinitely and enjoy them today, tomorrow and for the rest of our life. Besides that, we work with the belief that in 200 years the future generations will enjoy and benefit from our work, which is at the same time our passion. The criteria we use for the selection of our best mothers concern mostly to the desirable qualities of these plants and not to their origin, lineage or pedigree.

With these exceptional plants we then perform traditional breeding and also modern sex reversal methods in feminized plants to obtain 100% autoflowering and 99,9% feminized populations.

At Sweet Seeds® we are a pioneer seed bank in the development and improvement of the modern feminized autoflowering varieties. We trusted these new genetics since the day when the first autoflowering seeds fell in our hands.

Since 2007, when we started with our first experiments with autoflowering seeds, as Sweet Seeds®’ breeders we realized the immense potential of the autoflowering characteristic of these short and fast cannabis plants. That was the reason why we began experimenting and crossing these primitive autoflowering strains with our bank of selected clones, with the final goal of obtaining 100% autoflowering plants with the cannabinoid levels and aromas of our beloved elite clones.

The first generation of this type of Sweet Seeds® autoflowering varieties was presented in the course of the 2009 and 2010 seasons: Speed Devil Auto®, Fast Bud Auto® and Big Devil Auto®. These three varieties originated a tremendous success to the seed bank.

Speed Devil Auto® surprised the cannabic scene for being the first autoflowering plant to win an award in a contest. The jury of the I Copa de la Marina Baixa (Alicante 2010) blindly evaluated a sample that turned out to be Speed Devil Auto®, competing and winning against several photoperiod-dependent varieties that were presented at the contest, such as Jack Herer, White Widow, Diesel and other feminized modern polyhybrids.

In 2011 other autoflowering strain from Sweet Seeds®, Fast Bud Auto®, wins another first prize in the 1st Cannabis Cup Nature Grow, becoming the second autoflowering strain to achieve first prize in a contest, this time competing in a special category for autoflowering plants.

In 2014 the renowned magazine Soft Secrets awarded the prize “Auto del Año” (Auto of the Year) to the Big Devil® family. It was the first time that this specialized and international cannabic magazine awarded an autoflowering genetic. In the same year, the most modern of our Big Devil®’sBig Devil XL Auto®, obtained the 1st Prize in the III Copa Cannábica Expogrow Irún 2014.

These three first autoflowering varieties were used as a genetic base to introduce the autoflowering genes in the next generation of Sweet Seeds® autoflowering strains. We hybridized them with photoperiod-dependent elite clones to produce the second generation of autoflowering strains of our catalog. The successive generations of autoflowering strains represented the result of breeding programmes to introduce and stabilize the autoflowering trait in some of the best and most famous Sweet Seeds® genetics.

The autoflowering varieties arrived to the cannabic scene and they are here to stay, taking over their well deserved place, in the Hall of Fame of Cannabis Varieties..

What is the meaning of the different Generations that identify the Sweet Seeds®’ Autoflowering strains?

When we identify our autoflowering strains in different genetic generations (3G, 4G, 5G, etc...) we refer to generational steps and not to the generations strictly speaking. We establish a new generational step every time the presence of Cannabis ruderalis genetic in our autoflowering varieties is reduced. It usually occurs due to the cross with the photoperiod-dependent genetics.

Every time we cross an autoflowering genetic with a photoperiod-dependent genetic we gather 50% of the genetic of each of the parentals in the resulting hybrid, which is to say that in each cross we reduce the primitive genetic of Cannabis ruderalis in 50%, as the autoflowering parental only transfers half of its genetic contents to the offspring.

Regarding the first autoflowering generation used by Sweet Seeds® as a start material to introduce the autoflowering genes in the rest of the autoflowering strains that we have developed since then, we think that it could feature 25% of genetics coming from Cannabis ruderalis (this is something that we suspect, but we can not determine with certainty). When we used these genetic lines for breeding with elite clones from our bank of mothers, in the resulting hybrids from this cross we ended up with only 12,5% of Cannabis ruderalis genetics and we designate these new genetics as 2G (second generation), due to the fact that a substantial genetic evolution occurred regarding to the first generation that featured 25% of Cannabis ruderalis.

On the same way, the 3G varieties feature 6,25%, the 4G feature 3,125%, the 5G feature 1,562%, and so on. Every time we cross a last generation autoflowering genetic line with a photoperiod-dependent elite clone, we reduce in 50% the amount of Cannabis ruderalis genetics present in the resulting hybrid.

At present time the percentage of Cannabis ruderalis genetics left in the modern Sweet Seeds® autoflowering varieties is minimal and in that minimal segment we can find the genes that determine the autoflowering and the fast life cycle characteristics.

The genetic Re-Evolution of the autoflowering strains

With the arrival of autoflowering strains, as cannabis breeders we were forced to return to breeding from seed lines or populations as these strains don’t allow selection and keeping clones due to their autoflowering characteristic.

As Sweet Seeds® breeders we keep working with all our autoflowering strains, keeping them in constant evolution. Mainly due to the need to select the best specimens in each generation to use as parentals in the following generation. Given the wide genetic variations presented by cannabis in general and the modern autoflowering strains in particular, it is essential to select generation by generation in order to avoid undesirable genetic drifts.

Photoperiod-dependent genetics remain much more stable as years go by because we use selected elite clones to produce the commercial seed. In the production of photoperiod-dependent feminized seeds about 99% of the breeders use elite clones and not seed populations. We always use the same elite clones to produce each variety. Always using the same parentals has its benefits because the results are easily predictable, they are always the same. Only when a breeder finds an elite clone that contributes better characteristics to the offspring, while keeping the variety’s characteristic traits, a parental can be substituted, but this is not common at all. The drawback of always using the same parentals is that this way the commercial seed populations never evolve and the genetic frequencies remain constant by using the same source of genetics.

On the other hand we, the breeders who work with autoflowering genetics, can not keep in clone form the best specimens that we find, so we have to work with seed populations. This forces us to a permanent work of parental selection, not only during the development of breeding and improvement, but also every time that the commercial seeds are reproduced. Depending on the selected parentals, these populations can undergo genetic drifts in one or other direction, without keeping the genetic frequencies present in the commercial seed.

This way we keep these autoflowering seed populations in constant evolution. This turns the breeding work with these genetics into a much more exciting and personal work for the breeder. In this case the breeder has the option of performing selective pressure to take the seed population to the ideal and more desirable traits.

From our point of view there are two main reasons that led to the quality improvement in these autoflowering genetics, from the first wild primitive Cannabis Ruderalis genetic lines until the arrival of last generation autoflowering strains. First of all, the previously mentioned condition of working from seed populations and selecting the parentals in each generation, as this requires that the population is under constant evolution to the extreme of desirable traits as long as there is selective pressure from the breeder and variability in the gene pool. And secondly, the hybridization between autoflowering genetic lines with the best photoperiod-dependent clones resulting from decades of selection.

Development of new autoflowering strains and Inheritance of the autoflowering trait

Since we, the Sweet Seeds®’ breeders, started to understand the immense potential of the autoflowering trait confined in these small varieties, we started crossing them with our best photoperiod-dependent elite clones, searching for automatic flowering plants but with a quality at least similar to the one found in our beloved photoperiod-dependent mothers. The creation of new autoflowering strains was performed by hybridizing autoflowering genetics with selected photoperiod-dependent elite clones from our bank of mothers.

When we hybridize an autoflowering genetic with a photoperiod-dependent clone, the first goal is to fix the autoflowering trait in 100% of the hybrid population. This is relatively simple because this trait behaves as if it only depended on a single gene and shows typical mendelian inheritance. The autoflowering trait is recessive, so in the first filial generation of the hybrid no autoflowering specimen appears. It is necessary to reproduce this generation with itself to find 25% of autoflowering specimens in its offspring. Crossing these specimens found in the second filial generation with each other, we obtain the third filial generation featuring 100% of autoflowering specimens.

Parental selection in autoflowering seeds takes place in every generation and starts very early, when seeds germinate. When they are seedlings we eliminate all the specimens that show malformations or any kind of deficiency. During growth we continue with the parental selection, eliminating all the specimens that show undesirable traits. During flowering we keep eliminating the parentals where we observe undesired traits and in the end we will only have the ones that turn out to be the most productive, aromatic, resinous and, in general, the group of plants that feature the agronomical, organoleptic and chemotypic characteristics which gets us closer to the initial ideal goals.

When we perform these hybridizations to introduce the autoflowering trait in a new photoperiod-dependent genetic, at Sweet Seeds® we often use a selection of the best specimens from a feminized autoflowering population of plants as pollen donors. These specimens are subjected to sex reversal procedures that allow us to obtain the male flowers. And as pollen receptors we use the elite clone in which we want to introduce the autoflowering genes.

In the first programmes of selection and improvement of our first autoflowering strains at Sweet Seeds® we exceptionally used regular seeds (producing males and females). But from then on all our breeding work with automatic strains have been performed in absence of males. By other words, the pollen receptors have always been females and the pollen donors have always been females to which the sex has been reversed (only to obtain the pollen). These type of crosses bring about populations of feminized seeds, also known in genetic terms as ginoics. This technique ensures a very high femininity with very residual hermaphroditism occurrences detected in the lines developed through the use of this method.

On the other hand not all cannabis varieties and not all the specimens within a variety respond well to sex reversal techniques. Performing the whole procedure with females and reverse the sex from the pollen donors in each generation allows for a big advantage to the breeder who seeks an autoflowering and feminized commercial seed. The advantage lays on the fact that with this we ensure that in the end of the breeding programme the plants originated by the resulting seeds will have a good response to the same sex reversal technique, needed to reproduce the autoflowering and feminized commercial seeds.

If we were to perform the whole procedure with females and males (regular seeds), we could come to the conclusion that when the variety is finished and we want to cross some females with each other to obtain an autoflowering and feminized commercial seed, these wouldn’t have a good response to the sex reversal technique, producing very few or nonexistent viable pollen and consequently very few seeds, if any at all. Working throughout the whole programme with reversed females as pollen donors, we perform selective pressure in each generation over the parentals that feature good response to the sex reversal technique and that are capable of producing viable and abundant pollen, carrying on these traits to the next generation. With this, at the end of the breeding programme, the variety will feature a good response to the sex reversal technique.

The End

If you reached to this point of the text we would like to wish sweet and happy harvests. But we would also like to remind you that cannabis is a magical plant that has evolved by human hand since the beginning of times and is always ready to kindly return all the care and favours that the humans may give.

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