When to Harvest Buckwheat
Buckwheat is harvested when the grains are mature, even though the plant is still green. Start looking closely at the grain in the 10th and 11th week. The field may still be green, or even flowering, when the filled grains are ripe and the lower leaves have fallen off of the plants. Use this rule of thumb: harvest when 3/4 of the seeds are brown and the groat inside is firm. Some of the first seeds will probably be lost, and many will be immature. Look at them closely, because many of the green or light brown hulls are empty and should be disregarded.
The main concerns for harvest timing are lodging and shattering. The risk of lodging increases quickly as the seeds get heavier, the leaves fall, and the winds become stronger. Shattering occurs in over-mature plants and causes much of the grain to be lost if harvest is delayed too long. The harvest window is therefore fairly brief.
Pictures of maturing buckwheat seeds
Because of the way buckwheat ripens, immature seeds occur on the plant at harvest. Harvesting should be done when 3/4 of the seeds are ripe. Inspect the seeds closely, and count only filled seeds. There will often be many empty green hulls from late flowers, so if you only take a quick look, you are likely to underestimate the stage of maturity of the seeds.
When 3/4 of the seeds are brown and hard, the crop should be cut for windrowing or direct combining.