Popcorn sprouts are loaded with cytokinin which promotes cell division in the plants roots and shoots showing to increase the yields of crops. It's also induces a plants resistance to pathogens like pm etc. So generally good 1st and 3rd week of flower (well how I do it) . Coconut water is also a good source of Cytokinin but pretty expensive. You'll want your auxin exchange tapered off into the 1st week of flower and start promoting flower development by increasing cytokinins.
As a general sprout feed I use barley throughout (rich in amino acids) and alfalfa sprout teas only in veg. A good source of natural auxin can be gotten from willow extract (fermented willow juice) and is a great feed for vegetative stage of your plants growth cycle