Thank you for your support and for visiting my web site. During the winter, your house plants still need light. With the sun lower in the sky, it shines further into your room through your windows. This free solar heat will warm the room during the daytime, but is not stored into the evening at all. Since the evening and night are the coldest times, this is when the heating load on your furnace or heat pump is greatest.
Moist soil is an excellent medium to store solar heat.
Put your larger floor plants in dark pots and local them by a window. The dark pot tends to absorb more of the sun's heat during the days. The soil will not get too hot, but it store some of the heat. The rest of the sun's heat will warm your room in the daytime. When the sun goes down, the warm soil will slowly radiate its stored heat out into the room throughout the evening.