Once you've cut all the corstalks you can, the next step is to trim the "leaves" to length. This is not a very scientific process. All you need is a pair of scissors. Trim the green artificial needles to varying lengths as seen in the photo. It doesn't look like much yet, but in the next step you'll see the dramatic transformation from pine needle to corn stalk. You may want to practice on a few stalks with different lengths to find the look that's best for you.
A word of caution with this simple step - it can get very messy in a hurry! The plastic pine needles have a lot of static and will stick to just about anything. If you've ever had an artificial Christmas tree you may already know this. Now imagine taking that tree and cutting off hundreds of those little needles! Work over a trashbag and have a vacuum handy.