We have great produce for kales, chard, collards, beets, radish and such. Many varieties. But i can't even look at the bagged salad stuff. Always one leaf variety in those mixes that is soggy rotten. No flavor. Not even near the sell by date. And $$
I have buckwheat seed. Not tested yet. My bulk spices are from MountainRose
and organic.
https://www.mountainroseherbs.com/catalog/herbs/bulk
I think fresh seed would be best for testing. I just soaked some corn seed for shoots. Older seed. Even fresh pea seeds do take a bit longer to get going. But once they do, wow they zip. Like a race to the light.
The salad and veg micro mixes are fast and the most satisfying. Basement farm to table almost daily. The rest is timing. Seed size does not mater. Most suppliers list by fast, med, and slow growers.