I have lived two different cold drafty old farm houses.
Both were well over a hundred years old. Both had flower beds around them.
Both had full basements.
I used to pile straw about a foot deep over the flower beds and up against the house. More to protect the foundation walls from getting pushed in by frost than to save the roses. Then when it snowed the straw would be covered by snow up to three feet most winters
In the spring I used to rototill the half rotted straw into my garden.

I only had wood heat in those houses and as I said, they were drafty, almost unheatable.
If you left a jug of milk on the table overnight it would have ice in it in the morning.
Yet even if I was away for a month the basements never froze, I never had frozen pipes, and if I pulled back the snow and straw the flower beds would have been diggable in the coldest months of the year.
Straw and snow are great insulators and the ground in most places around the world is about 41 degrees fahrenheit.

I also had fewer mice in the house when I did this, I guess they preferred the straw to nest in than the uninsulated walls. I also had fewer weeds and more fishing worms in the flower beds for some reason.

I guess geothermal energy does not always need to be highly technical or pricey.