When winter comes around they will loose all of their leaves and go dormant. Plumerias are deciduous. Once dormant they no longer need light or water. Only a little drink of water every month or so to keep the roots from drying up. Be careful when watering because they do not use the water when dormant, so they can rot easily. Just keep them above 40 degrees farenheight and they should be fine. I would still put them in the window, so once they come out of dormancy they will have light, but be careful of drafts and cold air coming through the seams of the window. The cool air might freeze the plant, thus killing it. Hope this helps

Josh

SW Norway is approximately the equivalent latitude to Anchorage Alaska in the US. So a very difficult place for tropical plants to survive.

I would agree with Josh's post for the most part on established plants. But since these are very new seedlings I recommend keeping them growing over the winter with a lamp and heat mat. Being only 2 months old at this point they may not have enough stored energy to survive hibernating through 8 months of winter.

I didn't think they would take a frost or a freeze.

To Josh,

Thank you for your answer. I will keep them in the window then, and not water more than once a month. I do not know if there is a cool draft by the window yet. I will have to check for that.

To kms2,

Thank you for answer. The temperature inside should be steady at 71 degrees fahrenheit during the winter as long as the heating pump works, do I still need the heating lamp?

The winter here is very mild even though I live very far north. The gulf stream give us mild winters and wet summers. This summer we actually had up to 86 degrees (usually we have around 68 degrees). During winter it's usually around 32 degrees (Though some winters ago we saw 6,8 degrees) To sum it up, it is too cold to plant it outside, but the climate is not arctic.

I will look for a lamp, if I find one I will treat them as I would during summer. If not, I will try to do as Josh suggested.

To zackey,

You are right, therefore I have to have them inside, unfortunately. I will try to prune them as long as possible to maintain the size of them. I will also try to plant one once it is big enough, around 3-4 years old maybe. During winter I will try to cover it up with something isolating material.

I kept mine in front of a northern window because it was too big for the bathroom plant spa. Living room is out because of the cat. They go dormant anyways and lose their leaves, so I guess it didn't need any more light. It survived and is doing well outside now.

Norway,
Do you have a heat radiator you could place a flat stone or brick on? Then you could place your plant on the brick and it will radiate heat into the soil. I would use artificial light instead of trying to capture the 5-6 hours of winter daylight you may get.