Ex situ conservation

Part of a series on

Conservation

The long-term cold store of the National Laboratory for Genetic Resources Preservation at Fort Collins, Colorado (2016).

Cannabis conservation·Grow-out priorities·Populations

Threat Categories

Extinction

Genetic Threats

Genetic erosion·Genetic contamination·Introgression·Gene flow·Hybridisation·Population bottleneck·Genetic drift·Inbreeding depression

Habitat & Environmental Threats

Habitat loss

Eradication Tracking & Analysis

Eradication·Herbicide spraying of cannabis·Herbicide spraying in Mexico·Herbicide spraying in the United States·Herbicide spraying in Colombia·Herbicide spraying in Belize·Herbicide spraying in South Africa·US eradication abroad·Yukthiya·Cannabis eradication in Kirivong·Cannabis eradication in Fiji·Campaigns by country

International Enforcement

Cannabis prohibition·US eradication abroad·INCB

Legal & Policy

Farmers' rights·Access and benefit-sharing·Intellectual property·Single Convention on Narcotic Drugs·1988 Convention·Cannabis legalisation movement

Population Assessment

Minimum viable population·Population viability analysis·Effective population size

Conservation Monitoring

Population monitoring·Genetic monitoring

Conservation Methods - Ex Situ

Ex situ conservation·Gene bank·Cryopreservation·In vitro conservation·Core collection·Seed storage

Conservation Methods - In Situ

In situ conservation·On-farm conservation·Genetic reserve·Community seed bank·Feral and ruderal populations

Genetic Conservation

Germplasm·Genetic resources·Crop wild relative·Conservation genetics

Sampling & Collection

Germplasm collecting·Germplasm sampling

Preservation Strategies

Conservation prioritisation·Complementary conservation

Recovery & Restoration

Reintroduction·Genetic rescue

Conservation Science

Landrace conservation

Portal·Category

Ex situ conservation is the conservation of biological diversity outside its natural habitat. For plant genetic resources it takes place in seed gene banks, in in vitro gene banks or in live collections in field gene banks.^: 163

Cannabis seed survives drying and cold, which suits it to storage in gene banks. Regrowing it is harder. The plant is dioecious and pollinated by wind, so accessions grown near one another can cross. Matthew Welling and colleagues concluded in a 2016 review that the international drug conventions had contributed over more than 50 years to the "fractionation and erosion" of publicly accessible cannabis germplasm. John McPartland and Ernest Small called preservation in seed banks "an immediate priority" in 2020, given the state of wild populations in Asia.

Populations and their samples

Germplasm kept only in the field can be lost to genetic erosion, pests, disease or bad weather. McPartland and Small preferred in situ conservation for crops and their wild relatives in general. For cannabis they asked for both: collection in the centres of diversity of the Central and South Asian landraces and storage in seed banks.

The hemp collection of the National Plant Germplasm System at Geneva, New York, gathered since 2021, had passed 600 accessions from 35 countries by 2025. The collection's curator, Zachary Stansell, said in 2024 that some landraces have been under far less selection pressure than cultivated hemp and that feral populations, many of them from the American Midwest, may be a secondary source of diversity. In January 2026 INRA Maroc registered 106 samples of cannabis in the global information system of the Food and Agriculture Organization. All are classed as traditional cultivars or landraces. All but one were collected in the Rif Mountains in 2021 and 2023. The University of Mississippi keeps indoor-grown collections of living plants.

How long the seed lasts

Seed samples in moisture-proof foil bags in the cold vault at Fort Collins (2013).

Seeds that can be dried to a low moisture content and stored cold without damage are called orthodox.^: 165 Parihar and colleagues placed hemp seed in this group in 2014, after storing three lots bought in the market at Bageshwar in Uttarakhand for 36 months. Seed moisture and temperature determine how long seed lasts.

Cannabis seed in storage trials

Seed	Moisture	Temperature	Result	Source
Hemp, one lot	5.7 and 8.3%	10 °C and −10 °C	Viability kept for more than eight years
Hemp	5.7%, in sealed jars	21 °C	No fall in germination in six years
Three hemp cultivars, a medicinal marijuana strain and a ruderal strain	11%	20 °C	No germination within 18 months
Hemp, three lots	5%	10–40 °C (ambient laboratory, Delhi)	Starting viability kept for 36 months
Hemp, three lots	7%	15 °C	Starting germination kept for 36 months
Hemp, three lots	12%	−20 °C	Starting germination kept for 36 months

Small and Brookes ran their trial for 66 months. Cooling to 5 °C or drying to 6 per cent moisture did most of the work. Further cooling helped a little and further drying did not. Storage without oxygen brought no apparent benefit. Under uncontrolled conditions in a United States Department of Agriculture study, hemp seed held its viability for six years at Lind, Washington, where the seed's moisture stayed at or below 7.5 per cent, and lost viability rapidly at Princeton, Kentucky, and Beltsville, Maryland. Cockson and colleagues, who reported germination in some lots falling by half after one year of storage, advised less than 8 per cent moisture and 4 to 10 °C for storage of intermediate length.

At Geneva, seed is dried at 4 °C for six weeks, packed in envelopes and stored in a cold room at −20 °C. The collection was planned to keep backups at Fort Collins, Colorado, and to regrow any accession that fell below 2,000 seeds or 70 per cent viability. Long-term storage in gene banks generally aims at several decades or more between regrowings.^: 164 Reports on the Vavilov Institute collection in Russia put the life of its stored cannabis seed at about five years in 1994 and at three to four years before germination fell below 80 per cent in 1995. In 2016 Welling and colleagues considered systematic evidence of long-term viability in cannabis seed to be lacking.

Regrowing the seed

An accession is regrown to obtain a fresh sample with high viability and many seeds.^: 165 Male and hermaphrodite cannabis plants shed large amounts of pollen. One plant has been estimated to produce more than 350 million grains. Outdoor plots may need up to 5 km between them. Pollen may still cross that distance. Accessions from different latitudes need different day lengths to flower, which limits outdoor regrowing to certain times of year.

The Vavilov Institute and the International Hemp Association began a programme of regrowing in 1993. It set 1,000 plants and 200 g of seed as the standard for each accession and kept plots at least 2 km apart. Of the 172 accessions sown in 1993 and 1994, 11 met both standards. In all, 77 accessions held too little viable seed to raise 1,000 plants. Each year some samples failed to set seed, through poor ripening and theft. Accession 457, from Kattakurgan district in Uzbekistan, did not germinate when it was sown at Penza in 1997. By 1998, 379 of the collection's 496 accessions had been regrown. Very few had been lost, but several were down to a small stock of seed and, in Robert Clarke's words, "now must be multiplied from a possibly more limited genetic base". How many plants an accession needs to keep its variation is treated under effective population size.

The Geneva collection is regrown indoors over four to five months. Stansell brings as many plants as possible into each regrowing, because seed often arrives with no information on whether the sample comes from an inbred line or a variable population. Hemp cannot be regrown outdoors like an insect-pollinated crop, he said in 2024. The collection was adding growth chambers and beginning to build "hemp huts", outdoor structures that keep out pollen. Indoor rooms hold few plants. Welling and colleagues expected that allelic variation may fall with each cycle through genetic drift. Such loss has been seen in collections of barley, maize and common bean. Much of it appears to depend on the number of parents.

Plants, tissue and pollen

Cryogenic tanks at Fort Collins, holding plant tissue culture, seed and animal germplasm in liquid nitrogen or its vapour (2013).

Field gene banks are the usual choice for plants with seed that cannot be stored dry and cold, for plants that set few seeds and for those propagated vegetatively.^: 4 Cannabis growers keep clonal lines as living plants. A mother plant is held in a vegetative state under long days for many years and is replaced from time to time by one of its own cuttings. Producers report anecdotally that such lines lose vigour and cannabinoid content over time. Adamek and colleagues found somatic mutations that differed between parts of a single plant of the cultivar Honey Banana and suggested that they could contribute to the decline.

In vitro storage by slow growth serves for the short and medium term.^: 4 Axillary buds encapsulated in alginate have been kept for six months at 5 °C. Encapsulated nodal segments, stored for 150 days at 6 °C in the light, regrew at rates of 70 per cent from in vitro material and 90 per cent from plants grown outside culture.

Cryopreservation holds tissue in liquid nitrogen. At the University of Mississippi, 57 to 67 per cent of frozen shoot tips grew again after the best of three treatments, in work meant to extend to all the varieties held there. In a study of 13 commercial genotypes, 26.7 to 66.7 per cent of frozen nodal explants regrew. The resulting plants resembled controls in most major traits but differed in some minor cannabinoid and terpene profiles. Axillary buds of two cultivars reached 63 to 70 per cent regeneration in a 2026 study of the D-cryoplate method. Welling and colleagues suggested testing the freezing of seed, which has worked in several other species, as a way to avoid the cost and drift of regrowing.

Cannabis pollen mostly lost its viability within a week at 4 °C. Gaudet and colleagues dried it, mixed it with baked wheat flour and kept it in liquid nitrogen for four months with no further loss, although drying alone cost about half of its germination. Flowers pollinated with the treated pollen set seed. Stored pollen yields plants only through a cross, so a living plant must be at hand to receive it.^: 163

Losses from collections

Welling and colleagues described significant losses of hemp collections in the later 20th century, with likely genetic erosion. Collections in North America were confiscated, or in some cases reportedly destroyed, by regulatory authorities. Those that remained were short of funds for upkeep and regrowing. At the Vavilov Institute, lack of funding is thought to have compromised regrowing and cost unique diversity. The United States Department of Agriculture's cannabis accession PI 5021, received in 1900 from Shanghai, "no longer exists and can not be requested".

An accession can also change at regrowing without being lost. Gene flow between accessions at regrowing may be one reason why studies have reported a widely shared cannabis gene pool. McPartland and Small held that the germplasm of the Central and South Asian landraces outside their centres of diversity had been contaminated by widespread crossbreeding.

Law on holding cannabis

The Single Convention on Narcotic Drugs defines cannabis as the flowering or fruiting tops of the plant, leaving out seeds and leaves when not accompanied by the tops. Parties must limit the production, trade, use and possession of drugs exclusively to medical and scientific purposes and may not permit possession except under legal authority.^{: arts. 1, 4, 33} For Welling and colleagues, the barriers to a shared physical core collection were the limits on moving seed between signatory states and the lack of publicly accessible seed banks.

Federal law in the United States covers the seed itself. Its definition of marijuana takes in the seeds of the plant. Of seed it leaves out only hemp seed and "the sterilized seed of such plant which is incapable of germination". Marijuana has been in Schedule I since 1970. On 28 April 2026 marijuana in an approved drug product or under a state medical licence moved to Schedule III. All other marijuana stayed in Schedule I. Research with a Schedule I substance needs a registration and an approved protocol, which must state the security provisions for storing it.

Hemp was defined in 2018 as cannabis with no more than 0.3 per cent delta-9 THC by dry weight. An amendment enacted on 12 November 2025, with effect 365 days later, counts total THC including its acid form and excludes from hemp any viable seed of a plant above 0.3 per cent of that total. The Geneva collection screens its accessions against the 0.3 per cent limit. It sends seed free of charge for research anywhere in the world but not for individual, home or community gardening.

See also

• Effective population size
• Gene bank
• Genetic contamination
• Germplasm
• Grow-out priorities
• Seed lots
• In situ conservation
• On-farm conservation