Buckwheat appears to be a great wheat alternative.
Offered by John.
I found this related information from Cornell.
The general recommendation for harvesting buckwheat is when 70% of the grains are black.
Allelopathy helps buckwheat suppress weeds. Growers and extension staff often ask whether buckwheat has been shown to be allelopathic. We know that it shades out weeds well, and that summer tillage for buckwheat planting disrupts perennial weeds. The first report of actual allelopathy has finally come out. S.H. Eom at Kangwon University (in the buckwheat-growing region of Korea) has demonstrated that a compound called diethyl phthalate is produced by buckwheat and is responsible for weed suppression. This weed-suppressing compound is mainly in the stem rather than the shoots, so it is likely to be most active by suppressing weeds after the buckwheat is harvested. It was especially active on pigweed, and not particularly effective on plants in the mustard family.
Offered by Mike.