I use potato and have had much better yields with it. I put the potato flakes into the food processor to powederize them. This give high surface are in higher yields of micoworms. Oatmeal doesn't make as many worms. If you do use oatmeal, grind it to a powder that works better. Most important factor is mold. boil water before adding to the potatoes to sterilize BEFORE adding worm culture.I've heard that potatoes are a good choice of medium for microworms, I was going to try oatmeal and potatoes and see which way I like best. I saw a couple YouTube video experiments with microworms and different mediums. On of them did a side by side day by day comparison of microworms in oatmeal and microworms in potatoes. They both produced a lot but the oatmeal culture produced 2-3x as much. I really don't want super stinky oatmeal in my house and I don't have a ton of fish I have to feed it right now so I'm leaning towards potatoes right now but we shall see.