Locate and purchase seeded bananas. Check with local whole foods stores or farmer's markets to see if wild bananas are available or could be special ordered. Try using the Organic Store Locator (located in the Resource section) to find a nearby store.
Allow the bananas to ripen completely before attempting to harvest. Wait for the banana skin to turn yellow with brown spots, which indicates that the seeds are mature and ready for harvesting. Remove the banana peel and discard.
Set the banana into a bowl and gently squash with the back of a spoon. Be careful not to crush or break the seeds. Take notice that seed color will be brown to black and will typically present as round or oval shaped.
Mix some water into the bowl of squashed banana. Separate the pulp and seed mixture with your fingers. Remove the seeds and place on a paper towel. Throw out the banana pulp or recycle by using it to make banana bread.
Place the seeds in a very fine mesh strainer so they can't slip through. Wash the seeds under cold running water until clean. Place on a paper towel to dry. Store and seal in a plastic zipper bag.