When they curl into a circle, it's time to harvest the scapes. Cut them all the way down to about where the scape emerged
The scapes won't all grow at the same rate, so you'll need to harvest multiple times.
If you wait too long, a scape will start to straighten out and reach to the sky in preparation for flowering. They will get more fibrous and won't be as tender.
There are some good videos on how to harvest scapes on YouTube.
RayR wrote: