Scarlet runner beans (Phaseolus coccineus) add a splash of brilliant color to a vegetable or ornamental garden when trained to a trellis or support, as well as being a vegetable you can eat in one of three ways. The tender perennial plants, which grow on vines that reach up to 15 feet long, produce clusters of up to 20 1-inch bright red flowers. These develop into flat green pods picked and eaten before seeds swell when pods are plump, as fresh shelled beans or once the bright purple seeds are fully mature and dry. The dry seeds can also be used to propagate the open-pollinated heirloom plant.
Stop watering your scarlet runner beans once beans start to mature to speed the drying process.
Watch for plants to turn yellow and the pods to turn light brown. Scarlet runner beans are usually dry at about 55 days after planting.
Pick all the mature, dried pods and store them in a paper bag in a warm, dry place for several weeks to cure the seeds.
Break the seeds out of the pods once fully dry and cured. When you have a large number of pods to process, put them in a pillowcase or other cloth bag and beat the bag against a concrete floor or sidewalk or against the inside of a metal trashcan.
Sift the broken pieces of dried pod away from the large, bright purple-splotched seeds.
Store the seeds in paper envelopes inside a sealed jar in a cool place until it is time to plant them in late spring.