how much to water sweet potatoes?

i have some sweet potatoes in the poly tunnel, been in almost a month now. they sulked a bit for the first couple of days but seem to have recovered ok now.

however they don't really seem to be growing a great deal now.

i know these need high tempretures, which i usually have in the tunnel.

i'm just un sure of how much water they need? i've seen videos on you tude of people harvesting them and they look pretty dry.

thanks for any help and advice.