Most seed storage advice stops at “cool, dark and dry.” A more useful version uses numbers. Two rules of thumb from seed technology tell you roughly how much storage life a given change buys you. There is a drying step that most growers skip. And for pollen, published data show it is much more fragile than grower lore suggests. This guide is written for Thailand and the humid tropical lowlands of Southeast Asia, where ordinary room conditions are close to the worst case for seed.
1. What actually determines seed life: Harrington’s rules
There is a well-known relationship called Harrington’s rule of thumb. It is taught in seed technology and it underpins practical seed storage:
Seed longevity roughly halves for every 1% increase in seed moisture content, and for every 5–6 °C (about 10 °F) increase in storage temperature.
Know its limits. The rule is an approximation. It is usually stated as holding only between about 5% and 14% seed moisture and about 0 °C and 50 °C. Outside that window it stops working as a calculator.
Both variables are under your control, and they multiply rather than add. “Cool, dark and dry” does not tell you that.
Work through an example using the 6 °C step. Take seed at 10% moisture stored at 30 °C and move it to 6% moisture and 5 °C:
- Four halvings from moisture: 16×
- About four halvings from temperature (a 25 °C drop): 16×
- Combined: roughly 250× the storage life.
Treat that as an order of magnitude, not a prediction. It is still the difference between seed that is dead in a year or two and seed that is viable many years later.
Don’t over-dry. Cannabis seed is oil-rich. Oily seed holds less water at a given humidity than starchy seed, and drying it hard has its own risks. Below about 5% moisture the rule no longer applies and the gains level off. Over-dried seed can also become brittle and more easily damaged when it takes up water again. Never use heat or an oven to dry seed. Room-temperature silica gel (section 3) is enough.
2. Why this matters more in the tropics
In Bangkok and comparable cities in the humid tropical lowlands, room temperature runs 28–34 °C for most of the year. Relative humidity is frequently above 75%, and above 85% through the wet season.
Temperature: Seed kept in a drawer at around 30 °C is 18–20 °C warmer than seed in a cool European cellar at 10–12 °C. That is about three temperature-halvings, roughly eightfold shorter storage life from temperature alone.
Moisture: Because cannabis seed is oily, at 75–85% RH it settles at roughly 9–12% moisture. That is the upper part of Harrington’s range, which means faster decay. At the top of that band, fungal growth becomes a real risk.
The storage protocol is not optional in this climate. It is the difference between having a genetics library and having a box of dead seed.
3. The seed storage protocol
1. Dry first. This is the step most often skipped, and it matters most in the tropics. Seed sealed at ambient humidity is sealed at a high moisture content. Cooling it does not remove that water; it only makes condensation more likely. Put the seed in a sealed container with silica gel desiccant for one to two weeks at room temperature. Then move it to cold storage with fresh desiccant in the container.
2. Use an airtight, opaque container. Both properties matter. Label the outside with variety, source, quantity and date.
3. Store cold.
- Refrigerator (about 4–5 °C) for working stock you expect to use within a few years.
- Freezer (about −18 °C) for archive stock, only if the seed is well dried. Below 0 °C, Harrington’s arithmetic no longer applies, but cold storage of well-dried seed still slows ageing; seed genebanks store dried seed at freezer temperatures for long-term collections.
- Pad frozen seed carefully. Frozen seed is brittle. Hard knocks against other seeds or the container wall can crack the seed coat.
4. Let the container reach room temperature before opening it. A cold jar opened in a humid room condenses water directly onto the seed. This single mistake undoes an entire storage protocol, and it is the most common one. Take the jar out, leave it sealed for several hours, and only then open it.
5. Keep archive and working stock separate, and open them as rarely as possible. Every opening is a temperature and humidity excursion. Your archive should almost never be opened.
How long does it last in practice? Hard data for cannabis are scarce. One widely repeated breeder account describes ten G-13 Haze seeds produced in 1988 and germinated in 2001: one of the ten sprouted. That is an anecdote, not a calibration. The sample was ten seeds and the storage conditions are unknown. It does show that well-kept seed can stay alive for a long time, and that a single seed lot loses viability gradually.
4. The organic-seed longevity claim
Some TLO (True Living Organics) literature claims that organically grown seed stores far longer than seed grown on mineral nutrients: around 10 years refrigerated and about 20 years frozen, against roughly 2 years for mineral-fed seed. We found no published research that tests seed longevity against the mother plant’s fertiliser regime, in cannabis or in any other crop. Treat it as an untested claim and don’t plan a seed bank around it. Moisture and temperature, covered above, are the variables with evidence behind them.
5. Pollen storage
Collection and preparation (standard grower practice):
- Collect from male flowers roughly two weeks after the switch to 12/12. Tap the flower clusters onto parchment or foil.
- Sieve out all flower material. Pollen stored with plant debris can go mouldy.
- Dry the pollen for about a day in dry air, away from heat, direct light and draughts.
- Store it in a small glass bottle wrapped in black tape, labelled and dated, in the refrigerator.
- To use it, let the sealed bottle warm to room temperature first (several hours). Then quickly take what you need, reseal it and return it. This is the same condensation rule as for seed.
What the published data show. Gaudet D, Yadav NS, Sorokin A, Bilichak A, Kovalchuk I (2020). “Development and Optimization of a Germination Assay and Long-Term Storage for Cannabis sativa Pollen.” Plants 9(5): 665. doi:10.3390/plants9050665. The paper is open access. It reported:
- The highest germination at collection was 50%, from pollen collected at the mid-late flowering stage.
- At 4 °C, viability fell quickly. By 21 days, pollen from most collection stages was near zero. The best performer, pollen collected at mid flowering, retained about 22% germination.
- The cryoprotectants DMSO and glycerol were tested at 10%, 20%, 30% and 60%. All gave 0% germination after liquid-nitrogen storage.
- The protocol that worked long-term had four steps: vacuum desiccation at 5 kPa for 40 minutes, mixing with baked wheat flour at 1:10 by weight, and storage in liquid nitrogen (−196 °C). Germination after 24 hours and after four months was not significantly different from the non-frozen control. Pollen stored this way set seed in the flowers it was used on.
- Desiccation on its own roughly halved germination compared with fresh pollen.
How to read this. These are in-vitro germination figures. Fertility in practice may be higher, because in-vitro assays tend to under-read it. Even so, refrigerated pollen should be treated as a weeks-scale resource. Some grower literature claims at least six months of refrigerated viability. This study does not support that claim, though it does not rule it out either.
Practical consequences for breeders:
- Use fresh pollen wherever possible. Plan male and female timing to overlap rather than relying on pollen saved from a previous cycle.
- If you must store pollen, consider the flour carrier, even without liquid nitrogen. Pollen mixed at roughly 1:10 with baked, thoroughly dried flour is easier to handle and apply in small amounts. Note that the study only tested the flour carrier together with vacuum drying and liquid nitrogen. Its value in a home fridge is untested.
- Dry the pollen well before storage. Our reading is that drying matters at least as much as how cold the pollen is kept. The study does not report that as a finding. It does show that desiccation plus a carrier was what made long-term frozen storage work.
- Domestic freezer storage (−18 °C) remains untested as far as we can tell. Some grower literature advises against it. The study froze desiccated pollen in liquid nitrogen, which is a different situation.
6. Seed source
Grow from seed, then keep mother plants or take cuttings for long-term use. Cuttings brought in from elsewhere often carry powdery mildew, spider mites, aphids or thrips, along with viruses and pathogens. This applies with extra force in this region, where hop latent viroid and mite pressure are both significant and clone provenance is often undocumented.
Ask for the production date of the seed lot. A supplier who cannot tell you when the seed was produced cannot tell you where on the decay curve it sits. Also ask for parentage and stabilisation history.
We are not covering where to buy. Moving cannabis seed across borders is a customs and controlled-substance matter in every country in this region.
7. Checklist
Seeds:
- Dry with silica gel in a sealed container for 1–2 weeks at room temperature. No heat, and don’t chase extreme dryness.
- Use an airtight, opaque container with fresh desiccant inside.
- Label with variety, source, quantity and date.
- Refrigerate working stock (about 4–5 °C). Freeze archive stock (about −18 °C) only if well dried, and pad it.
- Keep archive and working stock separate.
- Always warm the sealed container fully before opening it.
- Minimise the number of openings.
- Ask suppliers for the production date.
Pollen:
- Collect about 2 weeks after the light flip, onto parchment or foil.
- Sieve out all flower material.
- Dry thoroughly.
- Consider mixing 1 part pollen with 10 parts baked, dried flour.
- Store airtight, light-proof, labelled, dated and refrigerated.
- Plan to use it within weeks, not months.
- Warm the sealed container fully before opening it.
8. What is verified and what is not
Established: Harrington’s rules of thumb, within roughly 5–14% moisture and 0–50 °C. The cannabis pollen findings of Gaudet et al. (2020) cited above, which are in-vitro germination data.
Unverified: The claim that organic seed outlasts mineral-fed seed, and all the figures attached to it. The claim that refrigerated pollen lasts six months. Domestic freezer storage of pollen. The G-13 Haze anecdote (n=10, storage unknown).
Sound practice: Airtight, dark, dry, cold, padded, and warmed before opening.
Does anyone here keep germination records by lot age and storage method? This climate is hard on seed, so a shared regional dataset would be worth more to breeders than any rule of thumb on this page. Post the lot age, storage protocol and germination percentage. Even a handful of real numbers would be a start.
For germination itself, see topic 391.
This article is technical horticultural information for readers operating legally in their jurisdiction. Cannabis seed and pollen are regulated as cannabis material in many countries, including for possession, import and export. In Thailand, the rules on possessing, propagating and cultivating cannabis fall under the Ministry of Public Health’s controlled-herb framework and the related notifications and licences. Importing cannabis seed into Thailand requires a permit. In countries where cannabis seed is prohibited (for example Vietnam), possessing or storing it is illegal and this guide does not apply. Check your local law. Nothing here is legal advice.