Cannabis is grown from one of two sources: a seed or a clone. Seeds carry genetic information from two parent plants that can be expressed in numerous different combinations, some like the mother, some like the father, and many presenting various traits from both. Generally, commercial cannabis producers will plant many seeds of one strain and choose the best plant. They will then take clones from that individual plant to get consistent genetics for mass production.
But for the typical homegrower, it may be easier to obtain seeds rather than clones. Growing from seed can produce a stronger plant with more solid genetics. Read on for more info on cannabis seeds.
Check out these additional resources for more info on cannabis seeds:
- A guide to buying cannabis seeds
- How to germinate cannabis seeds
- Male vs. female cannabis: How to determine the sex of your plant
Jump to a section in this article:
- What are cannabis seeds?
- What are feminized cannabis seeds?
- What are autoflower cannabis seeds?
- What are high-CBD cannabis seeds?
- What makes a cannabis seed high quality?
- Where can I buy cannabis seeds?
Cannabis can be either male or female—also called “dioecious”—but only females produce the buds we all know and love. However, for reproduction, the flower of a female plant must be pollinated by a male plant, after which the female flower produces seeds. Once the seeds are mature, the female plant begins to die, and seeds are either dropped to the ground where they germinate and grow into new cannabis plants the next spring, or they are harvested for processing into hemp seed oil, food products, or to be sown to become the next generation of plants.
To get the buds you find in medical and recreational stores, female cannabis plants are grown in an environment without males—or the males are removed from the area before they release pollen—so that they don’t pollinate and create seeds. This high-potency marijuana is traditionally known as “sinsemilla,” meaning “seedless.”
Some varieties of cannabis can produce male parts alongside female flowers on the same plant, especially if exposed to environmental stressors. These plants are known as hermaphrodites, and sometimes they can self-pollinate to create seeds.
Feminized cannabis seeds will produce only female plants for getting buds, so there is no need to remove males or worry about the plants getting pollinated. Feminized seeds are produced by causing the monoecious, or hermaphrodite condition in a female cannabis plant. The resulting seeds are nearly identical to the self-pollinated—or “selfed”—female parent, as only one set of genes is present.
This is sometimes referred to as “cloning by seed” and will not produce any male plants. This is achieved through several methods:
- By spraying the plant with a solution of colloidal silver, a liquid containing tiny particles of silver
- Through a method known as rodelization, in which a female plant pushed past maturity can pollinate another female
- Spraying seeds with gibberellic acid, a hormone that triggers germination (this is much less common)
Most experienced growers will not use feminized seeds because they only contain one set of genes, and these should never be used for breeding purposes.
Most cannabis plants begin flowering when the amount of light they are exposed to each day is reduced to about 12 hours. This mimics the sun going down in the sky as the season turns to autumn, causing plants to produce buds regardless of size or age. However, a species of the plant, called Cannabis ruderalis, which developed in extreme northern conditions without much sunlight, will begin flowering once the plant reaches a certain age—they automatically start flowering regardless of the amount of light they receive, hence the term “autoflower.”
Some breeders have crossbred the low-THC ruderalis with other more potent varieties to create autoflower strains that start blooming as soon as they reach maturity. These can be easier to maintain and can be especially great in northern climates where summers are short and cold and wet weather comes early in the fall.
Autoflower strains can be started in early spring and will flower during the longest days of summer to take advantage of the highest quality light available. Growers can fit in multiple autoflower harvests in the span of a regular harvest. One drawback, though: Autoflower strains are known for being less potent.
Cannabidiol, or CBD, is one of the chemical components—known collectively as cannabinoids—found in the cannabis plant. Lately, much has been made of the potential benefits of CBD for treating the symptoms of many diseases and conditions. Over the years, humans have selected plants for high-THC content, making cannabis with high levels of CBD rare. The genetic pathways through which THC is synthesized by the plant are different than those for CBD production.
Cannabis used for hemp production has been selected for other traits, including a low THC content, so as to comply with the 2018 Farm Bill. Consequently, many varieties of hemp produce significant quantities of CBD. As interest in CBD as a medicine has grown, many breeders have been crossing high-CBD hemp with cannabis. These strains have little or no THC, 1:1 ratios of THC and CBD, or some have a high-THC content along with significant amounts of CBD (3% or more).
Seeds for these varieties are now widely available online and through dispensaries. It should be noted, however, that any plant grown from these seeds is not guaranteed to produce high levels of CBD, as it takes many years to create a seed line that produces consistent results. A grower looking to produce cannabis with a certain THC to CBD ratio will need to grow from a tested and proven clone or seeds.
The most important factor in seed quality is genetics—to grow quality cannabis, you need good genetics. Some less scrupulous breeders will simply cross a nice female with a random male and sell the resulting seeds. A good breeder will take time to cross and backcross plants to stabilize the most desirable traits, while still producing an array of different phenotypes.
Seeds must also be allowed to fully mature before harvest. They also must be properly stored so they don’t acquire mold or other pathogens that can spoil them. Seeds should be stored in a cool, dark place and used within 16 months, or frozen for future use.
Really dedicated breeders have worked for years to create inbred lines, or IBLs, that will produce plants with very little noticeable difference. IBLs represent only a small fraction of cannabis seeds on the market, as they are generally used by breeders and not by producers.
Cannabis seeds can be found on numerous online seedbanks, but note that it is illegal to bring seeds into the US and Customs will seize any cannabis seeds that they find in packages or on a person. In legal and medical states, you may purchase seeds at a dispensary.
Learn more about how to buy cannabis seeds, the legality of doing so, and costs in our Guide to buying cannabis seeds.
This post was originally published on April 2, 2016. It was most recently updated on February 5, 2020.