Like plants, seeds have developed many strategies to help them survive through stressful conditions and harsh climates. One of these strategies is the development of a seed with an almost unbreakable outer layer surrounding the soft embryo inside. Species grown at SWNEC with this hard seed coat include basswood (Tilia americana), hawthorn (Crataegus sp.), bladdernut (Staphylea trifolia), and Kentucky coffee tree (Gymnocladus dioicus).
In nature these hard shelled seeds may pass through the digestive tract of an animal or sit on the ground for years before the seed coat begins to break down and the seed inside can germinate. This hard seed coat allows these species to spread across the landscape in the digestive systems of animals that eat them. Hard seed coats may have also evolved to offer protection for seeds from the heat of brushfires.
In order to grow these species sulphuric acid must be used to break down or scarify the hard seed coat. This is a careful process, over exposure to acid could easily destroy the seed coat and the soft embryo inside while under exposure may not allow the coat to break down enough to allow the embryo inside to grow.
After this process is complete the seed can then be stratified (put through a period of dormancy) and will hopefully germinate the following season.