STARTING AND SAVING BEAN SEEDS
Growing dry beans for seed is only slightly different than growing them for food.
Dry bush beans are self-pollinating—which means that the individual flowers are pollinated before they open—so you do not need to worry that any of the varieties you are growing in a given season will cross-pollinate. However, it is a good idea to separate varieties by about 25 feet in the garden. Never plant two varieties that have the same seed color next to each other. In the unlikely event that they cross you would not be able to detect this by looking at the seed.
Direct sow beans after the last frost in moderately fertile, well-worked, well-drained soil. Sow seeds about 1 inch deep, 2 inches apart, then thin to as much as 8 inches apart. Many gardening books recommend thinning to 4 inches apart, but plants will develop more fully and yield more with wider spacing.
Allow the pods to fully mature on the plants. Technically, with self-pollinating species, you would only need to harvest seed from one plant. But in order to insure the greatest possible genetic diversity in your seed crop, you should plan to harvest seed from as many plants as possible and then mix them together for next year’s seed stock.
It is important to prevent the bean pods from getting wet in their final stages of maturing. Some high-yielding bean plants get top-heavy and are at risk of flopping over later in the season. You can put stakes at the corners of the bed and run some string along the sides of the plants to support them. This is easy to do, not labor-intensive, and can help keep your bean crop from getting moldy and spoiled.
Once the seed pods are dry and crisp, but before they pop open on their own, harvest them and lay them in a shallow layer in cardboard flats until they are completely dry. You can thresh them as you have time in the fall. Lay the pods on a tarp and walk on them, or put them in a pillowcase and shuffle on them to release the seed. You can also put the beans in a bucket and tread on them to release the seeds. Make sure you remove all the beans from the pods, then it is quite simple to just lift the empty pods off the seeds, which will collect at the bottom. Once they are threshed, be sure to allow the seed to dry completely before packing for storage. This means leaving them at room temperature, out of direct sunlight, for at least two weeks.
Plant a couple of rows of beans, save some of the seed for re-planting, and you can eat the rest. Bean seeds will remain viable for several years if they are stored in a cool, dark, dry place.
Always be sure to label your seed carefully with the variety name, where the seed came from originally, and the year it was grown.