Saving seeds is an important way of promoting plant and food biodiversity at a time when just four companies – Corteva, ChemChina, Bayer and BASF – control 60% of the global seed market. Corporate dominance and patenting of seeds could lead to further losses of crop diversity, as companies focus on just a few crop varieties, such as corn, wheat and soy. Around 2010, hundreds of public libraries in the US and Canada started offering free seed exchanges, in an effort to preserve crop varieties that might be lost forever if not shared. When public libraries closed due to covid-19, that effort found a new form with people setting up small free seed libraries in their yards. Thousands of growers have put out their extra seeds for others to take, and their neighbours leave new seed varieties in exchange.