Cannabis Seeds Preservation: A Guide to Shelf Life and How to Properly Store Marijuana Seeds

Welcome to our article on storing cannabis seeds, a must-read for newcomers and experienced growers.

Cannabis seeds, like any other plant, have a lifespan that their storage conditions can significantly impact. Temperature, humidity, and light determine their viability over time; we will look at how to maintain this ideal environment. When done right, marijuana seeds can germinate even after 10 years in storage.

This guide aims to equip you with practical, easy-to-follow advice to ensure your seeds remain potent and productive, ready to sprout when you are.

How long do marijuana seeds last?

When stored properly, marijuana seeds can remain viable for 2-3 years and, in some cases, even up to 10 years when left undisturbed.

The time range around how long cannabis seeds can stay fresh and viable depends on storage conditions – particularly temperature, humidity, light exposure, and seeds’ genetics.

Some seeds with weak genetics may have a shelf-life of 6 months to a year. Similarly, the seeds will not last long if they are exposed to light or kept in a moist environment.

If you’ve bought seeds from a seed bank and they come in their packaging, you can leave them in and put them in a dark, dry spot. It is generally best to leave them undisturbed if you’re not planning to use your seeds immediately.

The specialised packaging helps maintain stable conditions like humidity, temperature, etc. Seed banks usually recommend planting within the year, but with extra care, as we will see below, you can increase the lifespan.

Conditions needed for storing marijuana seeds

Storing cannabis seeds does not require a lot – an airtight, lightproof container which is kept in dark, cool conditions will do the trick nicely.

The key is to create an environment that balances three critical factors: temperature, humidity, and light. Each element is pivotal in maintaining the seed’s viability and preventing premature germination.

Temperature

An ideal temperature range to store cannabis seeds varies between 4 to 8 degrees Celsius (39 to 46 degrees Fahrenheit). But this is not an absolute must. If you can store your seeds only at 10ºC, they will still last longer than when stored at 20ºC. Storing them at 5ºC will increase their lifespan than when kept at 10ºC.

Most home growers and professional breeders opt for 5ºC – 8ºC to store their seeds – which can be achieved in a fridge. If you cannot ensure such conditions, keep your seeds in a place with stable temperatures. Too many temperature fluctuations are not good for the seeds.

You can also store your weed seeds in freezing temperatures, going as low as -10ºC to -20ºC. This is particularly effective when storing seeds long-term for several years. In fact, the Svalbard Global Seed Vault – the world’s largest secured seed storage housing over 1 million samples – stores its seeds at -18ºC in very low moisture.

Here is a rule of thumb: The lower the temperatures, the longer the seeds will stay viable. But too cold temperatures can also cause the seeds to crack if mishandled. High temperatures, however, promote germination; they can cause the seeds to sprout and dry out.

Humidity & moisture

Low humidity is crucial to keep seeds from sprouting and prolonging their lifespan. High humidity means dealing with mould, fungi, and decay.

The table below highlights the effects of different humidity ranges on cannabis seeds.

Humidity levels	Effects of marijuana seeds
Above 60%	Too high humidity, chances of seeds becoming inactive and dying out, high risk of mould and seed decay
35%-60%	Accepted germination range
20%-35%	Ideal range for storing seeds – long term and short term
Less than 20%	Prone to issues like insects, pests, fungi, bacteria, excessive dryness, not ideal for germination

Moisture levels must also be considered when living in places with high humidity – like the tropicals or Thailand itself. In such cases, using moisture-proof, low-humidity containers is recommended – along with a mix of methods to reduce humidity. For example, placing a sachet of silica gels in the container is an excellent way to ensure low humidity.

Remember that cannabis seeds germinate in moist, humid conditions. The presence of moisture droplets in the seed storage box will cause the taproot to emerge.

Light

Light exposure can trick the seeds into thinking it’s time to germinate, leading to premature sprouting or damage. Seeds should be protected from light to maintain their viability – whether it is sunlight or artificial night. Storing seeds in a lightproof or opaque container, away from direct light, is crucial.

If you use a transparent container, wrap it in a light-blocking material and store it in a cool, dark place.

How to store cannabis seeds?

Cannabis seeds need a cold, dark, and dry place for storage; it is essential for maintaining their longevity and viability. But depending on whether you need to store the seeds for long-term or short-term, there are a few things you can do:

Short-term (6 months to 2 years)

For storing your seeds for up to a year, you don’t need to go to great lengths:

• Drawers & cupboards: A dark cupboard or drawer in your house with a stable temperature is suitable. Avoid areas prone to daily temperature changes, like garages or sheds.
• Wine Cellars/Basements: If using a cellar or basement, ensure it’s dry and stable in temperature. Use containers that are airtight, moisture-resistant, and block out light.
• Containers: Use any airtight container that blocks light, like photo-film canisters if not available.
• Environment: Ensure the storage area is dry and cool to prevent any moisture accumulation or heat exposure.

Long-term (2+ years):

When you intend to store seeds for a longer time, it’s crucial to create an environment that will preserve their viability:

• Refrigeration: To maintain a stable temperature, use a fridge, preferably a secondary one that isn’t opened frequently. Longer preservation can benefit from investing in dedicated mini-fridges.
• Specialised containers: Opt for airtight, lightproof, and moistureproof containers with moisture-absorbing materials like silica gel packets.
• Humidity and light control: Store in dark containers to protect from light. Ensure the fridge is dry; consider a No-Frost model to avoid humidity issues.

Additional considerations:

• Temperature consistency: Important for both short and long-term storage, with a longer lifespan requiring lower, stable temperatures. Avoid drastic changes in temperatures.
• Avoiding humidity: Moisture is detrimental to seeds. Use desiccants in containers to absorb excess moisture, along with using moistureproof boxes.
• Protect from light: Prevent light exposure to avoid triggering germination. Lightproof, opaque boxes kept away from light sources can go a long way in prolonging the shelf life of your cannabis seeds.
• Fridge humidity: Fridges can sometimes cause humidity issues. To counteract this, ensure your seeds are in airtight containers with desiccants. Regularly check the fridge for signs of moisture and consider using a hygrometer to monitor humidity levels inside.
• Oxygen: Oxygen and air promote germination in seeds. Hence it is important to keep them in airtight, almost vacuum-like conditions.

How to store your own marijuana seeds?

If you’ve grown your own cannabis seeds by crossing different varieties, they’ll need some time to dry before you store them. Freshly harvested seeds are often too moist for immediate use. Here’s a simplified approach:

• Dry them out: Leave your seeds at room temperature for two to three months. This helps reduce their moisture so they’re ready for storage.
• Keep an eye on them: Make sure they dry evenly without getting too dry or brittle. Avoid direct sunlight and high heat.
• Store properly: Once they’re dry, store your seeds in a cool, dark, and dry place. This keeps them viable until you’re ready to use them.

How to tell if your cannabis seeds have gone bad?

To determine if your cannabis seeds have gone bad, you can use several methods:

The sight test

• Colouration: Healthy seeds are typically dark and mottled, with black, brown, or grey patches. White or green seeds are usually immature and unlikely to germinate, while pale seeds may be too old. Older seeds look crumbly, dry, and withered.
• Waxy coating: Look for a shiny, waxy coating on the seed, which is a sign of a healthy seed.
• Cracks: Seeds should not have cracks. Cracked seeds are likely non-viable.
• Mildew: Examine seeds under a magnifying glass. A white, dusty powder indicates fungus, and the seeds should not be planted.

The touch test

Gently squeeze the seed between your thumb and forefinger. If it cracks under this slight pressure, it’s likely unusable and past its prime. Strong seeds that do not yield to any pressure in your hands have a better chance of germinating.

The germination test

The ultimate test of seed viability is to try germinating them. Plant the seed directly in the soil or use the paper towel method. You can learn more about marijuana germination methods in our detailed article.

Alternately, place your seeds in warm water for 1-2 hours. Seeds that float are likely bad and won’t grow, whereas seeds that sink are probably healthy. This test is simple and can check multiple seeds at once. Remember, only perform this test if you’re ready to germinate the seeds immediately, as water can damage the seeds.

What else to consider?

• Colour variability: Cannabis seeds can naturally vary in appearance, even within the same strain. Don’t be misled by size, shape, or colour differences into thinking one seed is of better quality than another.
• Hard shell: Mature seeds should have a hard outer shell and shouldn’t splinter under light pressure.
• Cracks or holes: Any visible cracks or holes on the shell can indicate the seed has gone bad.
• Mature seeds: Mature seeds tend to be darker in colour and have a hard outer shell. Immature seeds are often green with a soft shell.

Keep in mind that determining the viability of cannabis seeds isn’t an exact science. While these methods can give you a good indication, sometimes the only way to be certain is by attempting to grow the seeds.

Also, remember that cannabis seeds can exhibit natural variation even within the same strain, so slight differences in appearance do not necessarily indicate poor quality.

FAQs

Can old seeds germinate?

Yes, old cannabis seeds can germinate, but they might need a bit more care to get them to sprout.

One method to improve the germination rate of older seeds involves gently scuffing them with sandpaper. This process, known as scarification, helps to break down the seed’s hard outer shell, making it easier for moisture to get inside and start germination.

Another technique is briefly dipping the seeds in a hydrogen peroxide solution before planting. This step can sterilise the seeds and provide them with a burst of oxygen, which may aid in kickstarting germination.

Can cracked seeds germinate?

Germinating cracked seeds is very challenging to grow, giving them a high chance of failure. But there are things you can do.

You can try the paper towel method, where the seed is placed between moist paper towels and kept in a warm, dark place. This method allows you to closely monitor the seed and maintain optimal moisture levels, which might give a cracked seed a better chance of sprouting.

How long do cannabis seeds last?

Proper care and optimal storage conditions can prolong the lifespan of marijuana seeds to 10 years.

What does a healthy cannabis seed look like?

Healthy cannabis seeds are usually dark in colour with brown, black, or grey spots. They are usually mottled, featuring a tiger stripe or tortoise-shell pattern. They should have a hard, shiny outer shell and feel robust when squeezed gently. Immature seeds tend to be green and softer.

Can you tell the sex of a cannabis seed?

No, you cannot determine the sex of a cannabis plant from the seed. The sex of cannabis plants is not identifiable until the pre-flowering stage. There are myths and misconceptions about identifying the sex of a seed by its appearance, but these are unreliable.

What’s the best way to store cannabis seeds?

The best way to store cannabis seeds is in an airtight container in a cool, dry, and dark place. Refrigeration is ideal, especially in a fridge that isn’t opened frequently. Protect the seeds from light and moisture, and consider using desiccants to control humidity.