What are garlic scapes? Could you suggest something else?

If it helps, this is what my scape pesto looks like after I've made it -- so in the absence of scapes, I think you'd want some sort of allium green as a substitute!

They are the flower stems that shoot up from a bulb of garlic. If they get trimmed off before they flower, they are edible and have a more mild garlic flavor. (This is a helpful: https://food52.com/blog/3975-down-dirty-garlic-scapes.) And I haven't figured out a good substitute but I've been thinking about. My best guess would be some sort of combination of either: garlic cloves and scallion greens or garlic cloves and chives.

Hi! Garlic scapes are essentially stems that grow from the tops of garlic. They have a grassy, garlicky flavor. In this recipe, I think scallions could make a nice substitution. You might want to add some grated cheese (like Parmesan or pecorino) to the pesto, to tame the oniony flavor.

They're the long, flower bearing stems that garlic produces, usually in late spring or early summer.