I mix pollens when I've had no luck setting a pod so far or if it is an extremely hot day, and I think nothing will set but I'd like to try anyway. Some cultivars had more potent pollen than others so when I'm down to the last few buds, I put whatever pollen I have in my hand that day on it...and that will sometimes be two or three different pollens. Difficult pollens include KING CRAB and easy to set pollens include MISS MAYHEM in my garden. I usually regret doing that later, because I'd rather know the pollen parent of all my seeds.