Harvest buckwheat as close to the first frost in the autumn as possible; this will increase the yield of ripened seeds.
Use garden shears or hedge clippers -- depending on how big of a crop you have planted -- and cut the stalks about three-fourths of the way from the top of the plant.
Allow the buckwheat stalks to dry for a day or two; this will make it easier to harvest the seeds.
Shake the buckwheat stalks vigorously over a large white sheet. Grab a handful of buckwheat stalks and whack them onto the sheet. Remove any seeds as they come loose.
Separate the ripened buckwheat seeds from the unripened seeds and debris. Place the unripened seeds in a bowl and let them sit in warm place with access to sunlight for a few days while they ripen.