Two New Hens and how to train them to use the nest box

[cinnamongrrl]

Hi! I'm very new to chickens but so far my girls seem pretty happy. We adopted three chicks, two of which turned out to be roosters. We traded them to a neighbor for two hens that were already laying. Our third is a hen who (to my knowledge) has yet to lay her first egg. We just got the new hens a few days ago, and they've acclimated well. They're laying....but in a hen-made nest outside the coop. Today one laid in the coop, but on the floor, in straw, not in the nest box. I'm working on making the nest box a little cozier (painting it dark inside, etc) so hopefully that will help, but beyond putting fake eggs in it, what else can I do to encourage them to lay in the nest box NOT on the ground outside! Not that egg hunts aren't kind of fun....but for the long-run I'd rather know where they'll generally be....

Thank you!