I bought some bulbs from Costco, don't remember what kind. I started them in the house. They have green leaves. When I put them out after the last frost do they go in sun or shade in zone 5?
It makes a difference what kind they are in my somewhat limited experience. Most seem to like full sun as long as they get plenty of water, but a few seem to prefer some shade, so if you can figure out what you have it would help.
I just got some at Costco as well; the ones I got were labeled "Alocasia odora"; I got them to compare with the A. odora that I have been using in my breeding programs. Costco also had some Colocasia bulbs (green leaf) for sale. So my guess is your plant is either that Colocasia or Alocasia odora. If the leaves are soft, matte-green, and attached more or less perpendicularly to the petiole, they are Colocasia; if they are shinier without a matte look and held parallel to the petiole, they are Alocasia. Look at the picture of Alocasia odora on my site and compare the leaves to those you have and you might be able to confirm the ID.
Here is a link that might be useful: Aroidia Research - Alocasia odora page
It is a Colocasia. Thanks Lari Ann! They are over 3 feet tall so they need to go outside soon.