You need to be able to remove the pups with some roots attached. In my experience, I've noticed that when trying to cut them out, any corm and roots are really tucked in close to the mother plant. This means you need to go in at a sharp angle with your shovel, and deep. Then you should be able to get down in there and work it out with some roots intact. I've also noticed that the pups will thrive even with just a little root obtained. They are pretty tough plants.