It's abundantly obvious on frosty mornings that simple shelters do wonders for keeping the ice off things like seedlings, tender plants, citrus trees, the ground and paws.
We use this principle in the fledgling citrus grove to protect the young trees. Frosts only occur here for about 3 months of the year so in our typical slapdash fashion we haven't bothered to construct anything permanent. Hopefully in a few years the trees will be big and tough and grown up enough to face their own frost demons so they won't need our help. It all looks a bit Steptoe and Son, with various lengths of old canvas, random lengths of unused fabric, damaged horse rugs, assorted tarpaulins and off-cuts of shadecloth propped haphazardly over any plant that needs it. Still, it works.
The trees don't need to be kept warm, not by human standards anyway. 2 - 3 degrees above freezing is enough to deter damage and the makeshift covers ensure the ice crystals don't touch the trees. The cats prefer ice crystals not to touch them either.