Feminized seeds are popular because they promise to produce female plants nearly 100% of the time. In cannabis cultivation, only female plants produce the desired cannabinoid-rich flowers, making the exclusion of non-flowering male plants a significant advantage. This genetic certainty simplifies the growing process by eliminating the need to identify and remove males early in the cycle. This efficiency leads many cultivators to wonder if seeds produced by these female plants, if allowed to self-pollinate, carry the same female-only guarantee as the commercial seed they originated from.
The Process of Feminized Seed Creation
Breeders create feminized seeds by intentionally causing a female plant to produce viable pollen, a process known as sex reversal. Cannabis sex is determined by chromosomes: females carry two X chromosomes (XX), while males carry one X and one Y chromosome (XY). By using a female plant to generate pollen, the Y chromosome is removed from the breeding equation, ensuring all resulting seeds only contain XX chromosomes.
Sex reversal is commonly achieved by applying chemical solutions like Silver Thiosulfate (STS) or Colloidal Silver to the female plant. These silver-based compounds inhibit ethylene, a plant hormone important for female flower development. By blocking ethylene, the plant’s hormonal balance shifts, causing it to develop male reproductive organs, or pollen sacs, instead of female flowers.
The pollen collected from these chemically-induced male flowers is genetically female, carrying only X chromosomes. This pollen is used to pollinate another female plant or to self-pollinate the same plant. The resulting commercial feminized seeds are known as the F1 generation (a cross between two female parents) or the S1 generation (if the parent pollinated itself). This engineered process ensures the offspring inherit only the potential for female sex expression.
Are Seeds Produced by Feminized Plants Guaranteed Female
Seeds produced by a feminized plant that has been forced to self-pollinate are genetically female, possessing the XX chromosome pairing. This process is called “selfing,” and the resulting progeny are referred to as S1 seeds, standing for the first selfed generation. Since the parent plant only had X chromosomes, the pollen it produced only contained X chromosomes, making the genetic outcome overwhelmingly female.
However, the guarantee of femaleness is not absolute, and the stability differs significantly from commercially produced F1 seeds. The parent plant that created the S1 seeds was chemically or environmentally stressed to force pollen production. This stress-induced breeding process increases the genetic predisposition for the resulting S1 seeds to exhibit intersex traits, or hermaphroditism, later in life.
While S1 seeds will grow into female plants, their stability under environmental pressure is compromised. The parent plant used for self-pollination may not have been genetically stable enough to withstand sex reversal without passing on a higher tendency for intersex expression. Therefore, the probability of S1 seeds developing both male and female flowers later in their life cycle is significantly higher than a professionally bred seed. Commercial feminized seeds (F1) are produced from two distinct, highly stable female lines to minimize this inherited instability.
Genetic Stability and Risks of Secondary Seeds
The primary risk associated with growing S1, or secondary, seeds is their increased genetic susceptibility to express intersex traits under stress. An S1 seed inherits the full genetic makeup of a single parent, including any underlying tendency for hermaphroditism. If the parent plant was prone to developing male flowers when stressed, that tendency is concentrated and passed on to the S1 generation.
Environmental stressors are the major trigger for this instability, including light leaks during the dark cycle, temperature fluctuations, or severe nutrient deficiencies. When the S1 plant experiences these suboptimal conditions, its inherent genetic instability can manifest as the development of male pollen sacs, often referred to as “herms.” The presence of these male flowers can pollinate the rest of the crop, causing the female flowers to become seeded.
This potential for crop loss and pollen contamination is why commercial breeders avoid using S1 seeds for mass production. While S1 seeds are useful for preserving the specific traits of a single mother plant, they are not recommended for reliable, large-scale, or long-term cultivation. For the average grower, planting secondary seeds introduces a greater level of risk and requires more stringent control over the growing environment to mitigate instability.