Science Into Practice - Extending acorn storage

Pedunculate oaks only produce good seed crops every three-to-eight years. As oak seeds are difficult to store, the challenge for growers is balancing supply for future years.

Oak seeds have a high moisture content and lose the ability to germinate when the content drops below 38%. However, keeping them in "wet-storage" conditions (low temperatures and high humidity) to reduce water loss means the seeds continue to respire. This environment can prove ideal for certain fungi, such as Ciboria batschiana.

Research project HNS 197 has been investigating two different ways of extending the storage life of acorns - an anti-transpirant coating or wax to reduce water loss or storing them in special bags to reduce respiration.

The coatings selected were the commercially available anti-transpirant, Wiltpruf, beeswax, a microcrystalline wax and soya wax. The four bags tested were either polyethylene, a biopolymer with or without perforations and polyester with aluminium cook bag.

Germination capacity was tested under laboratory conditions. Untreated acorns achieved a less than 5% germination rate after 24 weeks. Beeswax achieved a 16.7% germination rate, with microcrystalline wax achieving 25.7% after 24 weeks. Improvements could potentially be made by modifying the formulas.

Soya wax was ineffective because it made a thin, brittle coating. Polythene and non-perforated biopolymer bags caused fermentation due to oxygen starvation.

Perforated biopolymer bags lost water and after 36 weeks germination was below 10%. After 60 weeks, 46% of acorns in polyester/aluminium bags were capable of germination. In nursery conditions after 12 weeks storage, the perforated biopolymer bags performed best, with a seedling emergence rate of 49%.

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