Finding the best containers for long-term seed storage

Once dried, seeds need to be stored in hermetically sealed containers. If containers are not effectively sealed, seeds will gradually absorb moisture and their storage life will be reduced.

Seed banks may use a variety of containers, made of glass, metal or plastic. There are advantages and disadvantages to all of these materials. Just as important as the material is the seal that can be achieved between the container and its lid. Screw lids allow ease of access but may occasionally loosen during freezing or thawing. Much more effective are lids with natural rubber or bromobutyl seals that can be clamped or crimped onto the container.

The Millennium Seed Bank project uses a simple and quick method of testing containers adapted from that by Gómez-Campo (2002), and the results obtained are similar. Freshly dried self-indicating silica gel is placed into test containers. The containers are sealed and transferred to high humidity conditions (e.g. an incubator set at 20°C, 95% RH). The colour of the silica gel is checked regularly over a 2-3 week period. If it changes colour this shows that moisture has been absorbed, or, in other words, that the container leaks and would be unsuitable for long-term seed storage.

Other factors to take into account when selecting storage containers are seed numbers and seed/fruit size and shape. These criteria help determine the expected volume of the collections and thus the range of container sizes required. The shape of the container is also important: containers with a wide neck allow easier access for large and irregular shaped seed. Within the seed bank, square containers pack more effectively than cylindrical ones.

Cost is often a significant factor. Most containers can be re-used, especially if peelable labels are used.

Key findings:

• Glass storage jars with natural rubber seals performed best in MSB tests.
• Most plastic storage containers leak and should be avoided.
• Tri-laminate aluminium foil bags perform well if an effective heat seal is achieved.
• Double packing small containers within larger jars is a convenient and effective way of storing small volumes of seed.
• Self-indicating silica gel sachets provide an effective and cheap method of detecting leaks.

Further information:

Gómez-Campo, C. (2002). Long-term seed preservation: the risk of selecting inadequate containers is very high. Monographs ETSIA, Univ. Politéchnica de Madrid 163: 1-10

Technical information sheet:Selecting containers for long-term seed storage

Manger, KR, Adams, J and Probert, RJ, (2003). Selecting seed containers for the Millennium Seed Bank Project, pp 637-652. In: RD Smith, JD Dickie. SH. Linington, HW Pritchard &. R.J Probert (eds) Seed conservation: turning science into practice. Royal Botanic Gardens, Kew, UK.