Can you pack house plants in checked luggage?

I have not read or heard anything saying you cant. I have seen people carry them in their lap though.

Where as there might not be regulations regarding domestic flights, there are restrictions regarding travelling to foreign countries.

Simple diseases like various fungi or insects, parasitic or not, are not supposed to cross borders. This in particular important when one fly from one place to another where these organizms normally would not be able to go without help.

There are warnings about this on airports and ferry places in Norway, Denmark, Sweeden, although some people do not heed the warnings and think that it does not matter.

Plants that may seem fine can be a jungle of various organizms too small for the human eye to notice. For these to cross borders can in worst case scenario become a big problem.

Where as you in most cases can actually get away with doing it, I would strongly advice against it due to the risk of contamination of destination.