"There are other ferns that grow like this," Ylva says. "But if it's not like these ones, it might not be good to eat, is the thing. Wrong types. Some of them are poisonous. Even these ones are a little bit poisonous, but that's why you boil them and then throw away the water. It takes the poison out and then they're safe."

She is not a chef, but she does know these things.

"You have to know what you're picking," Ylva says, "but you need to not pick what you don't know, too."