Pick the bean pods when their color changes from green to brown or tan. Feel the pods before picking to ensure they are dry and papery. The beans inside need to be swollen and hard.
Line a large tray with newspaper sheets. Place the bean pods on the tray in a single layer.
Dry the beans in the pod for two weeks. Any moisture trapped within the pods evaporates during this time.
Break open the pods and shake out the beans into a bowl. Scarlet runner bean seeds are mottled with black and purple markings.
Press on the beans with your fingernail to check that they are fully dry. Your nail won't dent fully dried runner beans.
Place the beans in an airtight container. Store in a cool, dark place until you are ready to plant them.