I sprout during the winter. Have done wheat, barley, BOSS, millet, popcorn, and deer forage mix, including the one that is heavy on the brassicas.
My favorites are a mix of barley and BOSS.
I find it cheapest to simply buy a bag of feed grain. You need to be sure that it is not heat treated, and that it is intended for feed, not for planting.
For myself, I sprout lentils, and alfalfa or a seed mix from the health food store.
Your chickens would be in heaven if you shared some of your alfalfa sprouts


Ben, dunno it's my first try. I have learned a lot from others here and that photo shows one of my mistakes, putting more than one layer of seed in the tray. I guess once I get it right a 12" x 12" tray one seed layer deep will be a good snack for one day. As I understand you only want to provide a portion of their diet as greens.
JT
It only takes 8 days to grow sprouts, I'm hoping to get setup to do it this winter.
