I have started my sweet potato slips way too early. I am in zone 6; can’t plant till May, and they are already 8-10 inches
Newburg Mo 65550
Certified GKH Gardening Expert
It will be best to keep them in container and under horticultural lighting. You can cut them in half when they get too tall. This will help them to bush out more anyway, which will give you better production. Just keep them under good lighting until you can put them out for the year.
This article will help you with their care in a container until you can put them out: https://www.gardeningknowhow.com/edible/vegetables/sweet-potato/sweet-potato-container-crops.htm