Hi sarakay13
I'm in zone 4b, not ready to plant potatoes yet, but your potato plants are beautiful.
Harvesting potatoes is fun! You will wait until 2 weeks after bloom and wait for the blossoms to have dropped off the plant - that is when the new potatoes are forming below the soil surface. Do you want to harvest small new potatoes or mature finished potatoes? If you want to wait for the large potatoes, then wait for the plant to yellow & die back.
Either way, you'll probably say 'I need to grow more potatoes next time!'